On April 23, 2023 the sky erupted with a massive solar storm, bringing the aurora to millions of people around the word.
On April 23 warnings went out alerting aurora watchers that a solar storm was imminent. And as the sky darkened that night locations all across the Northern and Southern Hemispheres were treated to a great sky show.
When we see this on our phone apps, we know we’ll get a great show. This was the auroral oval, lit up red, as the display was underway at my location in Alberta, Canada.
The strength of the interplanetary field (Bt) was high and the direction of the field (Bz) was well south, all welcome indicators of a superb show.
Sure enough, as it got dark that night, and from my location after the clouds cleared, an aurora was underway covering much of the sky.
The aurora moved south to occupy just the southern half of the sky, but with incredible ribbons crossing from east to west, rippling and pulsating off and on. Seeing patches of aurora pulse off and on and flaming up to the zenith is not uncommon toward the end of a substorm outburst. But this was the first time I can recall seeing pulsating ribbons.
At times, there was a dark ribbon across the sky, as the aurora formed a gap in its curtains, looking like a “dark aurora.”
The view looking straight up is always the most jaw-dropping when an aurora fills the sky. Rays and curtains converge at the magnetic zenith to form a “corona.”
I shot with three cameras, taking stills, time-lapses, and real-time movies. I edited them together here in a music video. Enlarge to full screen to view it. I hope you enjoy it!
With the Sun ramping up in activity, we should get more great shows of Northern – and Southern! – Lights around the world in the next few years,
In a detailed review, I test a “holy trinity” of premium Canon RF zoom lenses, with astrophotography the primary purpose.
In years past, zoom lenses were judged inferior to fixed-focal length “prime” lenses for the demands of astrophotography. Stars are the severest test of a lens, revealing optical aberrations that would go unnoticed in normal images, or even in photos of test charts. Many older zooms just didn’t cut it for discerning astrophotographers, myself included.
The new generation of premium zooms for mirrorless cameras, from Canon, Nikon and Sony, are dispelling the old wisdom that primes are better than zooms. The new zooms’ optical performance is proving to be as good, if not better than the older generation of prime lenses for DSLR cameras, models often designed decades ago.
The shorter lens-to-sensor “flange distance” offered by mirrorless cameras, along with new types of glass, provide lens designers more freedom to correct aberrations, particularly in wide-angle lenses.
While usually slower than top-of-the-line primes, the advantage of zoom lenses is their versatility for framing and composing subjects, great for nightscapes and constellation shots. It’s nice to have the flexibility of a zoom without sacrificing the optical quality and speed so important for astrophotography. Can we have it all? The new zooms come close to delivering.
A good thing, because with Canon we have little choice! For top-quality glass in wide-angle focal lengths at least, zooms are the only choice for their mirrorless R cameras. As of this writing in late 2022, Canon has yet to release any premium primes for their RF mount shorter than 50mm. Rumours are a 12mm, 24mm, 28mm, and 35mm are coming! But when?
The three zooms I tested are all “L” lenses, designating them as premium-performance models. I have not tested any of Canon’s “economy” line of RF lenses, such as their 24mm and 35mm Macro STM primes. Tests I’ve seen suggest they don’t offer the sharpness I desire for most astrophotography.
Contributing to the lack of choice, top-quality third-party lenses from the likes of Sigma (such as their new 20mm and 24mm Art lenses made for mirrorless cameras) have yet to appear in Canon RF mount versions. Will they ever? In moves that evoked much disdain, Samyang and Viltrox were both ordered by Canon to cease production of their RF auto-focus lenses.
For their mirrorless R cameras, Canon has not authorized any third-party lens makers, forcing you to buy costly Canon L glass, or settle for their lower-grade STM lenses, or opt for reverse-engineered manual-focus lenses from makers such as TTArtisan and Laowa/Venus Optics. While they are good, they are not up to the optical standards of Canon’s L-series glass.
I know, as I own several RF-mount TTArtisan wide-angle lenses and the Laowa 15mm f/2 lens. You can find my tests of those lenses at AstroGearToday.com. Look under Reviews: Astrophotography Gear.
The trio of RF lenses tested here work on all Canon EOS R-series cameras, including their R7 and R10 cropped-frame cameras. However, they will not work on any Canon DSLRs.
Two of the lenses, the RF15-35mm F/2.8 and RF70-200mm F/4, are designs updated from older Canon DSLR lenses with similar specs. The RF28-70mm F/2 does not have an equivalent focal length range and speed in Canon’s DSLR lens line-up. Indeed, nobody else makes a lens this fast covering the “normal” zoom range.
Together, the three lenses cover focal lengths from 15mm to 200mm, with some overlap. A trio of zooms like this — a wide-angle, normal, and telephoto — is often called a “holy trinity” set, a popular combination all camera manufacturers offer to cover the majority of applications.
However, my interest was strictly for astrophotography, with stars the test subjects.
NOTE: CLICK or TAP on a test image to download a full-resolution image for closer inspection. The images, while low-compression JPGs, are large and numerous, and so will take time to fully load and display. Patience!
I tested the trio of lenses on same-night exposures of a starry but moonlit sky, using the 45-megapixel Canon R5 camera mounted on a motorized star tracker to follow the rotating sky. With one exception noted, any distortion of stars from perfect pinpoints is due to lens aberrations, not star trailing. The brighter moonlit sky helped reveal non-uniform illumination from lens vignetting.
I shot each lens wide-open at its maximum aperture, as well as one stop down from maximum, to see how aberrations and vignetting improved.
I did not test auto-focus performance, nor image stabilization (only the RF28-70mm lacks internal IS), nor other lens traits unimportant for astro work such as bokeh or close focus image quality.
I also compared the RF15-35mm on same-night dark-sky tests against a trio of prime lenses long in my stable: the Rokinon 14mm SP, and Canon’s older L-series 24mm and 35mm primes, all made for DSLRs.
Each of the Canon “holy trinity” of zoom performs superbly, though not without some residual lens aberrations such as corner astigmatism and, in the RF28-70mm, slight chromatic aberration at f/2.
However, what flaws they show are well below the level of many older prime lenses made for DSLR cameras.
The RF lenses’ major optical flaw is vignetting, which can be quite severe at some focal lengths, such as in the RF70-200mm at 200mm. But this flaw can be corrected in processing.
These are lenses that can replace fixed-focal length primes, though at considerable cost, in part justifiable in that they negate the need for a suite of many prime lenses.
The performance of these and other new lenses made for mirrorless cameras from all brands is one good reason to switch from DSLR to mirrorless cameras.
Lens Specs and Applications
Canon RF15-35mm F/2.8 L IS USM
The Canon RF15-35mm F/2.8 L is made primarily for urban photography and landscapes by day. My main application is using it to take landscapes by night, and auroras, where its relatively fast f/2.8 speed helps keeps exposure times short and ISO speeds reasonably low. However, the RF15-35mm can certainly be used for tracked wide-angle Milky Way and constellation portraits.
The lens weighs a moderate 885 grams (31 ounces or 1.9 pounds) with lens hood and end caps, and accepts 82mm filters, larger than the 72mm or 77mm filter threads of most astrophoto-friendly lenses. Square 100mm filters will work well on the lens, even at the 15mm focal length. There are choices, such as from KASE, for light pollution reduction and star diffusion filters in this size and format. I have reviews of these filters at AstroGearToday.com, both here for light pollution filters and here for starglow filters.
Canon offers a lower-cost alternative in this range, their RF14-35mm. But it is f/4, a little slow for nightscape, aurora, and Milky Way photography. I have not tested one.
Canon RF28-70mm F/2 L USM
The big Canon RF28-70mm F/2 is aimed at wedding and portrait photographers, though the lens is suitable for landscape work. While I do use it for nightscapes, my primary use is for tracked Milky Way and constellation images, where its range of fields of view nicely frames most constellations, from big to small.
I justified its high cost by deciding it replaces (more or less!) prime lenses in the common 24mm, 35mm, 50mm, and 85mm focal lengths. Its f/2 speed does bring it into fast prime lens territory. It’s handy to have just one lens to cover the range.
Canon offers a lower-cost alternative here, too, their RF24-70mm. But it is f/2.8. While this is certainly excellent speed, I like having the option of shooting at f/2. An example is when using narrowband nebula filters such as red hydrogen-alpha filters, where shooting at f/2 keeps exposures shorter and/or ISOs lower when using such dense filters. I use this lens with an Astronomik 12-nanometre H-α clip-in filter. An example is in one of the galleries below.
While a clip-in filter shifts the infinity focus point inward (to as close as the 2-metre mark with the RF28-70mm at 28mm, and to 6 metres at 70mm), I did not find that shift adversely affected the lens’s optical performance. That’s not true of all lenses.
Make no mistake, the RF28-70mm is one hefty lens, weighing 1530 grams (54 ounces or 3.4 pounds). Its front-heavy mass demands a solid tripod head. Its large front lens accepts big 95mm filters, a rare size with few options available. I found one broadband light pollution filter in this size, from URTH. Otherwise, you need to use in-body clip-in filters. Astronomik makes a selection for Canon EOS R cameras.
Canon RF70-200mm F/4 L IS USM
The Canon RF70-200mm F/4 is another portrait or landscape lens. I use it primarily for bright twilight planet conjunctions and moonrise scenes, where its slower f/4 speed is not a detriment. However, as my tests show, it can be used for tracked deep-sky images, where it is still faster than most short focal length telescopes.
The RF70-200mm lens weighs 810 grams (28 ounces, or 1.75 pounds) with lens hood and caps, so is light for a 70-to-200mm zoom. It is also compact. At just 140mm long when set to 70mm, it is actually the shortest lens of the trio. However, the barrel extends to 195mm long when zoomed out to 200mm focal length.
Canon offers the more costly and, at 1200 grams, heavier RF70-200mm F/2.8 lens which might be a better choice for deep-sky imaging where the extra stop of speed can be useful. But in this case, I chose the slower, more affordable – though still not cheap – f/4 version. It accepts common 77mm filters, as does the f/2.8 version.
Canon RF15-35mm F/2.8 L IS USM
Like the other two zoom lenses tested, the RF15-35mm is very sharp on axis. Even wide open, there’s no evidence of softness and star bloat from spherical aberration, the bane of cheaper lenses.
Coloured haloes from longitudinal chromatic aberration are absent, except at 28mm and 35mm (shown here) when wide open at f/2.8, where bright stars show a little bit of blue haloing. At f/4, this minor level of aberration disappears.
Canon RF28-70mm F/2 L USM
The big RF28-70mm is also very sharp on-axis but is prone to more chromatic aberration at f/2, showing slight magenta haloes on bright stars at the shorter focal lengths and pale cyan haloes at 70mm in my test shots. Such false colour haloes can be very sensitive to precise focus, though with refractive optics the point of least colour is often not the point of sharpest focus.
At f/2, stars are a little softer at 70mm than at 28mm. Stopping down to f/2.8 eliminates this slight softness and most of the longitudinal chromatic aberration.
Canon RF70-200mm F/4 L IS USM
Unlike prime telephotos I’ve used, the RF70-200mm shows negligible chromatic aberration on-axis at all focal lengths, even at f/4. Stars are a little softer at the longest focal length at f/4, perhaps from slight spherical aberration, though my 200mm test shots are also affected by a little mistracking, trailing the stars slightly.
Stopping down to f/5.6 sharpens stars just that much more at 200mm.
The corners are where we typically separate great lenses from the merely good. And it is where zoom lenses have traditionally performed badly. For example, my original Canon EF16-35mm f/2.8 lens was so bad off-axis I found it mostly unusable for astro work. Not so the new RF15-35mm, which is the RF replacement for Canon’s older EF16-35mm.
To be clear – in these test shots you might think the level of aberrations are surprising for premium lenses. But keep in mind, to show them at all I am having to pixel-peep by enlarging all the test images by 400 percent, cropping down to just the extreme corners.
Check the examples in the Compared to DSLR Lenses section and in the Finished ImagesGalleries for another look at lens performance in broader context.
Canon RF15-35mm F/2.8 L IS USM
Surprisingly, this RF’s best performance off-axis is actually at its shortest focal length. At 15mm it exhibits only some slight tangential astigmatism, elongating stars away from the frame centre. At 24mm aberrations appear slightly worse than at the other focal lengths, showing some flaring from sagittal astigmatism and perhaps coma as well, aberrations seen to a lesser degree at 28mm and 35mm, making stars look like little three-pointed triangles.
The aberrations reduce when stopped down to f/4, but are still present, especially at 24mm, this lens’s weakest focal length, though only just.
While the RF15-35mm isn’t perfect, it outperforms other prime lenses I have, and that I suspect most users will own or have used in the past with DSLRs. Only new wide-angle premium primes for the RF mount, if and when we see them, will provide better performance.
Canon RF28-70mm F/2 L USM
The RF28-70mm’s fast f/2 speed, unusual for any zoom lens, was surely a challenge to design for. Off-axis when wide open at f/2 it does show astigmatism at the extreme corners at all focal lengths, but the least at 50mm, and the worst at 28mm where a little lateral chromatic aberration is also visible, adding slight colour fringing.
Sharpness off-axis improves markedly when stopped down one stop to f/2.8, where at 50mm stars are now nearly perfect to the corners. Indeed, performance is so good at 50mm, I think there would be little need to buy the Canon RF50mm prime, unless its f/1.2 speed is deemed essential.
With the RF28-70mm at f/2.8, stars still show some residual astigmatism at 28mm and 35mm, but only at the extreme corners.
Canon RF70-200mm F/4 L IS USM
The RF70-200mm telephoto zoom shows some astigmatism and coma at the corners when wide open at f/4, with it worse at the shorter focal lengths. While lens corrections have been applied here, the 200mm image still shows a darker corner from the vignetting described below.
Stopping down to f/5.6 eliminates most of the off-axis aberrations at 135mm and 200mm focal lengths but some remain at 70mm and to a lesser degree at 100mm.
This is a lens that can be used at f/4 even for the demands of deep-sky imaging, though perfectionists will want to stop it down. At f/5.6 it is similar in speed to many astrographic refractors, though most of those start at about 250mm focal length.
In the previous test images, I applied lens corrections (but no other adjustments) to each of the raw files in Adobe Camera Raw, using the settings ACR automatically selects from its lens database. These corrections brightened the corners.
In this next set I show the lenses’ weakest point, their high level of vignetting. This light falloff darkens the corners by a surprising amount. In the new generation of lenses for mirrorless cameras, it seems lens designers are choosing to sacrifice uniform frame illumination in order to maximize aberration corrections. The latter can’t be corrected entirely, if at all, by software.
However, corrections applied either in-camera or at the computer can brighten corners, “flattening” the field. I show that improvement in the section that follows this one.
Canon RF15-35mm F/2.8 L IS USM
In the wide-angle zoom, vignetting darkens just the corners at 15mm, but widens to affect progressively more of the frame at the longer focal lengths. The examples show the entire right side of the frame. I show the effect just at f/2.8.
Though I don’t show examples with the two wider zooms, with all lenses vignetting decreases dramatically when each lens is stopped down by even one stop. The fields become much more evenly illuminated, though some darkening at the very corners remains one stop down.
Canon RF28-70mm F/2 L USM
In this “normal” zoom, vignetting performance is similar at all focal lengths, though it affects a bit more of the field at 70mm than at 28mm. Again, while I’m not presenting an example, vignetting decreases a lot when this lens is stopped down to f/2.8. While the extra stop of speed is certainly nice to have at times, I usually shoot the RF28-70mm at f/2.8.
Canon RF70-200mm F/4 L IS USM
In this telephoto zoom, vignetting is fairly mild at the shorter focal lengths but becomes severe at 200mm, affecting much of the field. It is far worse than I see with my older Canon EF200mm f/2.8 prime, a lens that is not as sharp at f/4 as the RF zoom.
The faster RF70-200mm f/2.8 lens, which I had the chance to test one night last year, showed as much, if not more, vignetting than the f/4 version. See my test here at AstroGearToday.com. I thought the f/4 version would be better for vignetting, but it is not.
In this case, as the vignetting is so prominent at 200mm, I show above how much it improves when stopped down to f/5.6, in a comparison with the lens at f/4, both with no lens corrections applied in processing. The major improvement comes from the smaller aperture alone. For twilight scenes, I’d suggest stopping this lens down to better ensure a uniform sky background.
In this next set I show how well applying lens corrections improves the vignetting at the focal lengths where each of the lenses is at its worse, and with each at its widest aperture.
I show this with Adobe Camera Raw but Lightroom would provide identical results. I did not test lens corrections with other programs such as CaptureOne, DxO PhotoLab, or ON1 Photo Raw, which all have automatic lens corrections as well.
Canon RF15-35mm F/2.8 L IS USM
Applying lens corrections in Adobe Camera Raw certainly brightened the corners and edges, though still left some darkening at the very corners that can be corrected by hand in the Manual tab.
Canon RF28-70mm F/2 L USM
ACR’s lens corrections helped but did not completely eliminate the vignetting here. Corner darkening remained. Manually increasing the vignetting slider can provide that extra level of correction needed.
Canon RF70-200mm F/4 L IS USM
The high level of vignetting with this lens at 200mm largely disappeared with lens corrections, though not entirely. For deep-sky imaging, users might prefer to shoot and apply flat-field frames. I prefer to apply automatic and manual corrections to the raw files, to stay within a raw workflow as much as possible.
Same Focal Length Comparisons
With the trio of lenses offering some of the same focal lengths, here I show how they compare at three of those shared focal lengths. I zoom into the upper right corners here, as with the Corner Aberrations comparisons above.
RF15-35mm vs. RF28-70mm at 28mm
With both lenses at 28mm and at the same f/2.8 aperture (though the RF28-70mm is now stopped down one stop), it’s a toss up. Both show corner aberrations, though of a different mix, distorting stars a little differently. The RF28-70mm shows some lateral chromatic aberration, but the RF15-35mm shows a bit more flaring from astigmatism.
RF15-35mm vs. RF28-70mm at 35mm
The story is similar with each lens at 35mm. Stars seem a bit sharper in the RF15-35mm though are elongated more by astigmatism at the very corners. Lens corrections have been applied here and with the other two-lens comparison pairs.
RF28-70mm vs. RF70-200mm at 70mm
Here I show the RF28-70mm at f/2.8 and the RF70-200mm wide open at f/4, with both set to 70mm focal length. The telephoto lens shows a little more softening and star bloating from corner aberrations, though both perform well.
Compared to DSLR Lenses
Here I try to demonstrate just how much better at least one of the zooms on test here is compared to older prime lenses made for DSLRs. The Canon lenses are labeled EF, for Canon’s EF lens mount used for decades on their DSLRs and EOS film cameras. Both are premium L lenses.
I shot this set on a different night than the previous examples, with some light cloud present which added various amounts of glows around stars. But the test shots still show corner sharpness and aberrations well, in this case of the upper left corners of all frames.
Canon RF15-35mm at 35mm vs. Canon EF35mm L
The Canon EF35mm is the original Mark I version, which Canon replaced a few years ago with an improved Mark II model. So I’m sure if you were to buy an EF35mm lens now (or if that’s the model you own) it will perform better than what I show here.
Both lenses are at f/2.8, wide open for the RF lens, but stopped down two stops for the f/1.4 EF lens.
The zoom lens is much sharper to the corners, with far less astigmatism and none of the lateral chromatic aberration and field curvature (softening stars at the very corner) of the old EF35mm prime. I thought the EF35mm was a superb lens, and used it a lot over the last 15 years for Milky Way panoramas. I would not use it now!
Canon RF15-35mm at 24mm vs. Canon EF24mm L
Bought in the early years of DSLRs, the EF24mm tested here is also an original Mark I model, since replaced by an improved Mark II 24mm. The old 24mm is good, but shows more astigmatism than the RF lens, and some field curvature and purple chromatic aberration not present at all in the RF lens.
And this is comparing it to the RF lens at its weakest focal length, 24mm. It still handily outperforms the old EF24mm prime.
Canon RF15-35mm at 15mm vs. Rokinon 14mm SP
Canon once made an EF14mm f/2.8 L prime, but I’ve never used it. For a lens in this focal length, one popular with nightscape photographers, I’ve used the ubiquitous Rokinon/Samyang 14mm f/2.8 manual lens. While a bargain at about $300, I always found it soft and aberrated at the corners. See my test of 14mm ultra-wides here.
A few years ago I upgraded to the Rokinon 14mm f/2.4 lens in their premium SP series (about $800 for the EF-mount version). While a manual lens, it does have electrical contacts to communicate lens metadata to the camera. Like all EF-mount lenses from any brand, it can be adapted to Canon R cameras using Canon’s $100 EF-EOS R lens adapter.
The Rokinon SP is the only prime I found that beat the RF zoom. It provided sharper images to the corners than the RF15-35mm at 15mm. The Rokinon also offers the slightly faster maximum aperture of f/2.4 (which Canon cameras register as f/2.5). Vignetting is severe, but like the RF lenses can be corrected – Camera Raw has this lens in its database. What is not so easy to correct is some slight colour shift at the corners.
Another disadvantage, as with many other 14mm lenses, is that the SP lens cannot accept front-mounted filters. The RF15-35mm can.
Nevertheless, until Canon comes out with a 12mm to 14mm RF prime, or allows Sigma to, an adapted Rokinon 14mm SP is a good affordable alternative to the RF15-35mm.
All the RF lens bodies are built of weight-saving engineered plastic incorporating thorough weather sealing. There is nothing cheap about their fit, finish or handling. Each lens has textured grip rings for the zoom, focus and a control ring that can be programmed to adjust either aperture, ISO, exposure compensation or other settings of your choosing.
As with all modern auto-focus lenses, the manual focus ring on each lens does not mechanically move glass. It controls a motor that in turn focuses the lens, so-called “focus-by-wire.” However, I found that focus could be dialled in accurately. But if the camera is turned off, then on again, the lens will not return to its previous focus position. You have to refocus to infinity each time the camera is powered up, a nuisance.
Unlike some Nikon, Sony, Samyang, and Sigma lenses, none of the Canon lenses have a focus lock button, or any way of presetting an infinity focus point, or simply having the lens remember where it was last set. I would hope Canon could address that deficiency in a firmware update.
With all the zooms, I did not find any issue with “zoom creep.” The telescoping barrels remained in place during long exposures and did not slowly retract when aimed up. While the RF28-70mm and RF70-200mm each have a zoom lock switch, it locks the lens only at its shortest focal length.
Each lens is parfocal within its zoom range. Focus at one zoom position, and it will be in focus for all the focal lengths. I usually focus at the longest focal length where it is easiest to judge focus by eye, then zoom out to frame the scene.
FINISHED IMAGES GALLERIES
Here I present a selection of final, processed images (four for each lens), so you can better see how each performs on real-world celestial subjects. To speed download, the images are downsized to 2048 pixels wide.
As per my comments at top, the RF15-35mm is my primary nightscape lens, the RF28-70mm my lens for wide-field constellation and Milky Way shots, while the RF70-200mm is for conjunctions and Moon scenes. It would also be good for eclipses.
Image Gallery withCanon RF15-35mm F/2.8 L IS USM
Image Gallery withCanon RF28-70mm F/2 L USM
Image Gallery withCanon RF70-200mm F/4 L IS USM
CONCLUSIONs and recommendations
If you are a Canon user switching from your aging but faithful DSLR to one of their mirrorless R cameras, each of these lenses will perform superbly for astrophotography. At a price! Each is costly. But the cost of older EF lenses has also increased in recent months.
The other native RF L-series lenses in this focal length range, Canon’s RF50mm and RF85mm f/1.2 primes, are stunning … but also expensive. As I’m sure any coming RF wide-angle L primes will be, if and when they ever appear!
The cheaper alternative – not the least because you might already own them! – is using adapted EF-mount lenses made for DSLRs, either from Canon or other brands. But in many cases, as I’ve shown, the new RF glass is sharper, especially when on a high-resolution camera such as the Canon R5 I used for all the testing.
And there’s the harsh reality that Canon is discontinuing many EF lenses. You can now buy some only used. For example, the EF135mm f/2 L and EF200mm f/2.8 L are both gone.
Until Canon licenses other companies to issue approved lenses for their RF mount – if that happens at all – our choices for native RF lenses are limited. However, the quality of Canon’s L lenses is superb. I now use these zooms almost exclusively, and financed most of their considerable cost by selling off a ream of older cameras and lenses.
If there’s one lens to buy for most astrophotography, it might be the big RF28-70mm F/2, a zoom lens that comes close to offering it all: flexibility, optical quality and speed. The RF24-70mm F/2.8 is a more affordable choice, though I have not tested one.
If nightscapes are the priority, the RF15-35mm F/2.8 would see a lot of use, as perhaps the only lens you’d need.
Of the trio, the RF70-200mm was the lowest priority on my wish list. But it has proven to be very useful for framing horizon scenes.
The superb optics of these and other new lenses made for mirrorless cameras is one good reason to upgrade from a DSLR to a mirrorless camera, in whatever brand you prefer.
In an extensive technical blog, I put the Canon R6 mirrorless camera through its paces for the demands of astrophotography.
Every major camera manufacturer, with the lone exception of stalwart Pentax, has moved from producing digital lens reflex (DSLR) cameras, to digital single lens mirrorless (DSLM) cameras. The reflex mirror is gone, allowing for a more compact camera, better movie capabilities, and enhanced auto-focus functions, among other benefits.
But what about for astrophotography? I reviewed the Sony a7III and Nikon Z6 mirrorless cameras here on my blog and, except for a couple of points, found them excellent for the demands of most astrophotography.
For the last two years I’ve primarily used Canon’s astro-friendly and red-sensitive EOS Ra mirrorless, a model sadly discontinued in September 2021 after just two years on the market. I reviewed that camera in the April 2020 issue of Sky & Telescope magazine, with a quick first look here on my blog.
The superb performance of the Ra has prompted me to stay with the Canon mirrorless R system for future camera purchases. Here I test the mid-priced R6, introduced in August 2020.
NOTE: In early November 2022 Canon announced the EOS R6 MkII, which one assumes will eventually replace the original R6 once stock of that camera runs out. The MkII has a 24 Mp sensor for slightly better resolution, and offers longer battery life. But the main improvements over the R6 is to autofocus accuracy, a function of little use to astrophotographers. Only real-world testing will tell if the R6 MkII has better or worse noise levels than the R6, or has eliminated the R6’s amp glow, reported on below.
The Canon R6 has proven excellent for astrophotography, exhibiting better dynamic range and shadow recovery than most Canon DSLRs, due to the ISO invariant design of the R6 sensor. It is on par with the low-light performance of Nikon and Sony mirrorless cameras.
The preview image is sensitive enough to allow easy framing and focusing at night. The movie mode produces usable quality up to ISO 51,200, making 4K movies of auroras possible. Canon DSLRs cannot do this.
Marring the superb performance are annoying deficiencies in the design, and one flaw in the image quality – an amp glow – that particularly impacts deep-sky imaging.
The Canon R6 is superb for its:
Low noise, though not exceptionally so
ISO invariant sensor performance for good shadow recovery
Sensitive live view display with ultra-high ISO boost in Movie mode
Relatively low noise Movie mode with full frame 4K video
Low light auto focus and accurate manual focus assist
Good battery life
The Canon R6 is not so superb for its:
Lack of a top LCD screen
Bright timer display in Bulb on the rear screen
No battery level indication when shooting
Low grade R3-style remote jack, same as on entry-level Canon DSLRs
Image Quality Flaw
Magenta edge “amp glow” in long exposures
CHOOSING THE R6
Canon’s first full-frame mirrorless camera, the 30-megapixel EOS R, was introduced in late 2018 to compete with Sony. As of late-2021 the main choices in a Canon DSLM for astrophotography are either the original R, the 20-megapixel R6, the 26-megapixel Rp, or the 45-megapixel R5.
The new 24-megapixel Canon R3, while it has impressive low-noise performance, is designed primarily for high-speed sports and news photography. It is difficult to justify its $6,000 cost for astro work.
I have not tested Canon’s entry-level, but full-frame Rp. While the Rp’s image quality is likely quite good, its small battery and short lifetime on a single charge will be limiting factors for astrophotography.
Nor have I tested the higher-end R5. Friends who use the R5 for nightscape work love it, but with smaller pixels the R5 will be noisier than the R6, which lab tests at sites such as DPReview.com seem to confirm.
Meanwhile, the original EOS R, while having excellent image quality and features, is surely destined for replacement in the near future – with a Canon EOS R Mark II? The R’s successor might be a great astrophoto camera, but with the Ra gone, I feel the R6 is currently the prime choice from Canon, especially for nightscapes.
I tested an R6 purchased in June 2021 and updated in August with firmware v1.4. I’ll go through its performance and functions with astrophotography in mind. I’ve ignored praised R6 features such as eye tracking autofocus, in-body image stabilization, and high speed burst rates. They are of limited or no value for astrophotography.
Along the way, I also offer a selection of user tips, some of which are applicable to other cameras.
LIVE VIEW FOCUSING AND FRAMING
The first difference you will see when using any new mirrorless camera, compared to even a high-end DSLR, is how much brighter the “Live View” image is when shooting at night. DSLM cameras are always in Live View – even the eye-level viewfinder presents a digital image supplied by the sensor.
As such, whether on the rear screen on in the viewfinder, you see an image that closely matches the photo you are about to take, because it is the image you are about to take.
To a limit. DSLMs can do only so much to simulate what a long 30-second exposure will look like. But the R6, like many DSLMs, goes a long way in providing a preview image bright enough to frame a dark scene and focus on bright stars. Turn on Exposure Simulation to brighten the live image, and open the lens as wide as possible.
But the R6 has a trick up its sleeve for framing nightscapes. Switch the Mode dial to Movie, and set the ISO up to 204,800 (or at night just dial in Auto ISO), and with the lens wide open and shutter on 1/8 second (as above), the preview image will brighten enough to show the Milky Way and dark foreground, albeit in a noisy image. But it’s just for aiming and framing.
This is similar to the excellent, but well-hidden Bright Monitoring mode on Sony Alphas. This high-ISO Movie mode makes it a pleasure using the R6 for nightscapes. The EOS R and Ra do not have this ability. While their live view screens are good, they are not as sensitive as the R6’s, with the R and Ra’s Movie modes able to go up to only ISO 12,800. The R5 can go up to “only” ISO 51,200 in its Movie mode, good but not quite high enough for live framing on dark nights.
The R6 will also autofocus down to a claimed EV -6.5, allowing it to focus in dim light for nightscapes, a feat impossible in most cameras. In practice with the Canon RF 15-35mm lens at f/2.8, I found the R6 can’t autofocus on the actual dark landscape, but it can autofocus on bright stars and planets (provided, of course, the camera is fitted with an autofocus lens).
Autofocusing on bright stars proved very accurate. By comparison, while the Ra can autofocus on distant bright lights, it fails on bright stars or planets.
Turning on Focus Peaking makes stars turn red, yellow or blue (your choice of colours) when they are in focus, as a reassuring confirmation.
In manual focus, an additional Focus Aid overlay provides arrows that close up and turn green when in focus on a bright star or planet. Or you can zoom in by 5x or 10x to focus by eye the old way by examining the star image. I wish the R6 had a 15x or 20x magnification; 5x and 10x have long been the Canon standards. Only the Ra offered 30x for ultra-precise focusing on stars.
In all, the ease of framing and focusing will be the major improvement you’ll enjoy by moving to any mirrorless, especially if your old camera is a cropped-frame Canon Rebel or T3i! But the R6 particularly excels at ease of focusing and framing.
The key camera characteristic for astrophoto use is noise. I feel it is more important than resolution. There’s little point in having lots of fine detail if it is lost in a blizzard of high-ISO noise. And for astro work, we are almost always shooting at high ISOs.
With just 20 megapixels, low by today’s standards, the R6 has individual pixels, or more correctly “photosites,” that are each 6.6 microns in size, the “pixel pitch.”
By comparison, the 30-megapixel R (and Ra) has a pixel pitch of 5.4 microns, the 45-megapixel R5’s pixel pitch is 4.4 microns, while the acclaimed low-light champion in the camera world, the 12-megapixel Sony a7sIII, has large 8.5-micron photosites.
The bigger the photosites (i.e. the larger the pixel pitch), the more photons each photosite can collect in a given amount of time – and the more photons they can collect, period, before they overfill and clip highlights. More photons equals more signal, and therefore a better signal-to-noise ratio, while the greater “full-well depth” yields higher dynamic range.
Each generation of camera also improves the signal-to-noise ratio by suppressing noise via its sensor design and improved signal processing hardware and firmware. The R6 uses Canon’s latest DIGIC X processor shared by the company’s other mirrorless cameras.
In noise tests comparing the R6 against the Ra and Canon 6D Mark II, all three cameras showed a similar level of noise at ISO settings from 400 up to 12,800. But the 6D Mark II performed well only when properly exposed. Both the R6 and Ra performed much better for shadow recovery in underexposed scenes.
In nightscapes and deep-sky images the R6 and Ra looked nearly identical at each of their ISO settings. This was surprising considering the Ra’s smaller photosites, which perhaps attests to the low noise of the astronomical “a” model.
Or it could be that the R6 isn’t as low noise as it should be for a 20 megapixel camera. But it is as good as it gets for Canon cameras, and that’s very good indeed.
I saw no “magic ISO” setting where the R6 performed better than at other settings. Noise increased in proportion to the ISO speed. It proved perfectly usable up to ISO 6400, with ISO 12,800 acceptable for stills when necessary.
The flaw in many Canon DSLRs, one documented in my 2017 review of the 6D Mark II, was their poor dynamic range due to the lack of an ISO invariant sensor design.
The R6, as with Canon’s other R-series cameras, has largely addressed this weakness. The sensor in the R6 appears to be nicely ISO invariant and performs as well as the Sony and Nikon cameras I have used and tested, models praised for their ISO invariant behaviour.
Where this trait shows itself to advantage is on nightscapes where the starlit foreground is often dark and underexposed. Bringing out detail in the shadows in raw files requires a lot of Shadow Recovery or increasing the Exposure slider. Images from an ISO invariant sensor can withstand the brightening “in post” far better, with minimal noise increase or degradations such as a loss of contrast, added banding, or horrible discolourations.
To test the R6, I shot sets of images at the same shutter speed, one well-exposed at a high ISO, then several at successively lower ISOs to underexpose by 1 to 5 stops. I then brightened the underexposed images by increasing the Exposure in Camera Raw by the same 1 to 5 stops. In an ideal ISO invariant sensor, all the images should look the same.
The R6 did very well in images underexposed by up to 4 stops. Images underexposed by 5 stops started to fall apart, but I’ve seen that in Sony and Nikon images as well.
This behaviour applies to images underexposed by using lower ISOs than what a “normal” exposure might require. Underexposing with lower ISOs can help maintain dynamic range and avoid highlight clipping. But with nightscapes, foregrounds can often be too dark even when shot at an ISO high enough to be suitable for the sky. Foregrounds are almost always underexposed, so good shadow recovery is essential for nightscapes, and especially time-lapses, when blending in separate longer exposures for the ground is not practical.
With its improved ISO invariant sensor, the R6 will be a fine camera for nightscape and time-lapse use, which was not true of the 6D Mark II.
However, to be clear, ISO invariant behaviour doesn’t help you as much if you underexpose by using too short a shutter speed or too small a lens aperture. I tested the R6 in series of images underexposed by keeping ISO the same but decreasing the shutter speed then the aperture in one-stop increments.
The underexposed images fell apart in quality much sooner, when underexposed more than 3 stops. Again, this is behaviour similar to what I’ve seen in Sonys and Nikons. For the best image quality I feel it is always a best practice to expose well at the camera. Don’t count on saving images in post.
TIP: Underexposing by using too short an exposure time is the major mistake astrophotographers make, who then wonder why their images are riddled with odd artifacts and patten noise. Always Expose to the Right (ETTR), even with ISO invariant cameras. The best way to avoid noise is to give your sensor more signal, by using longer exposures or wider apertures. Use settings that push the histogram to the right.
LONG EXPOSURE NOISE REDUCTION
All cameras will exhibit thermal noise in long exposures, especially on warm nights. This form of noise peppers the shadows with hot pixels, often brightly coloured.
This is not the same as the shot and read noise that adds graininess to high-ISO images and that noise reduction software can smooth out. This is a common misunderstanding, even among professional photographers who should know better!
Long Exposure Noise Reduction (LENR) eliminates this thermal noise by taking a “dark frame” and subtracting it in-camera to yield a raw file free of hot pixels.
And yes, LENR does apply to raw files, another fact even many professional photographers don’t realize. It is High ISO Noise Reduction that applies only to JPGs, along with Color Space and Picture Styles.
The LENR option on the R6 did eliminate most hot pixels, though sometimes still left, or added, a few. LENR is needed more on warm nights, and with longer exposures at higher ISOs. So the extent of thermal noise in any camera can vary a lot from shoot to shoot.
When LENR is active, the R6’s rear screen lights up with “Busy,” which is annoyingly bright. To hide this display, the only option is to close the screen.
As with the EOS Ra, and all mirrorless cameras, the R6 has no “dark frame buffer” that allows several exposures to be taken in quick succession even with LENR on. Canon’s full-frame DSLRs have this little-known buffer that allows 3, 4, or 5 “light frames” to be taken in a row before the LENR dark frame kicks in a locks up the camera on Busy.
With all Canon R cameras, and most other DSLRs, turning on LENR forces the camera to take a dark frame after every light frame, doubling the time it takes to finish every exposure. That’s a price many photographers aren’t willing to pay, but on warm nights it can be necessary, and a best practice, for the reward of cleaner images.
TIP: If you find hot pixels are becoming more obvious over time, try this trick: turn on the Clean Manually routine for 30 seconds to a minute. In some cameras this can remap the hot pixels so the camera can better eliminate them.
Using LENR with the R6 did not introduce any oddities such as oddly-coloured, green or wiped-out stars. Even without LENR I saw no evidence of green stars, a flaw that plagues some Sony cameras at all times, or Nikons when using LENR.
Canons have always been known for their good star colours, and the R6 is no exception. According to DPReview the R6 has a low-pass anti-alias filter in front of its sensor. Cameras which lack such a sensor filter do produce sharper images, but stars that occupy only one or two pixels might not de-Bayer properly into the correct colours. That’s not an issue with the R6.
I also saw no “star-eating,” a flaw Nikons and Sonys have been accused of over the years, due to aggressive in-camera noise reduction even on raw files. Canons have always escaped charges of star-eating.
DSLRs are prone to vignetting along the top and bottom of the frame from shadowing by the upraised mirror and mirror box. Not having a mirror, and a sensor not deeply recessed in the body, largely eliminates this edge vignetting in mirrorless cameras.
That is certainly true of the R6. Images boosted a lot in contrast, as we do with deep-sky photos, show not the slightest trace of vignetting along the top or bottom edges There were no odd clips or metal bits intruding into the light path, unlike in the Sony a7III I tested in 2018.
The full frame of the R6 can be used without need for cropping or ad hoc edge brightening in post. Except …
EDGE ARTIFACTS/AMP GLOWS
The R6 did exhibit one serious and annoying flaw in long-exposure high-ISO images – a magenta glow along the edges, especially the right edge and lower right corner.
Whether this is the true cause or not, it looks like “amplifier glow,” an effect caused by heat from circuitry illuminating the sensor with infra-red light. It shows itself when images are boosted in contrast and brightness in processing. It’s the sort of flaw revealed only when testing for the demands of astrophotography. It was present in images I took through a telescope, so it is not IR leakage from an auto-focus lens.
I saw this type of amp glow with the Sony a7III, a flaw eventually eliminated in a firmware update that, I presume, turned off unneeded electronics in long exposures.
Amp glow is something I have not seen in Canon cameras for many years. In a premium camera like the R6 it should not be there. Period. Canon needs to fix this with a firmware update.
UPDATE AUGUST 1, 2022: As of v1.6 of the R6 firmware, released in July 2022, the amp glow issue remains and has not been fixed. It may never be at this point.
It is the R6’s only serious image flaw, but it’s surprising to see it at all. Turning on LENR eliminates the amp glow, as it should, but using LENR is not always practical, such as in time-lapses and star trails.
For deep-sky photography high-ISO images are pushed to extremes of contrast, revealing any non-uniform illumination or colour. The usual practice of taking and applying calibration dark frames should also eliminate the amp glow. But I’d rather it not be there in the first place!
The R6 I bought was a stock “off-the-shelf” model. It is Canon’s now-discontinued EOS Ra model that is (or was) “filter-modified” to record a greater level of the deep red wavelength from red nebulas in the Milky Way. Compared to the Ra, the R6 did well, but could not record the depth of nebulosity the Ra can, to be expected for a stock camera.
In wide-field images of the Milky Way, the R6 picked up a respectable level of red nebulosity, especially when shooting through a broadband light pollution reduction filter, and with careful processing.
However, when going after faint nebulas through a telescope, even the use of a narrowband filter did not help bring out the target. Indeed, attempting to correct the extreme colour shift introduced by such a filter resulted in a muddy mess and accentuated edge glows with the R6, but worked well with the Ra.
While the R6 could be modified by a third party, the edge amp glow might spoil images, as a filter modification can make a sensor even more sensitive to IR light, potentially flooding the image with unwanted glows.
TIP: Buying a used Canon Ra (if you can find one) might be one choice for a filter-modified mirrorless camera, one much cheaper than a full frame cooled CMOS camera such as a ZWO ASI2400MC. Or Spencer’s Camera sells modified versions of all the R series cameras with a choice of sensor filters. But I have not used any of their modded cameras.
A concern of prospective buyers is whether the R6’s relatively low 20-megapixel sensor will be sharp enough for their purposes. R6 images are 5472 by 3648 pixels, much less than the 8000+ pixel-wide images from high-resolution cameras like the Canon R5, Nikon Z7II or Sony a1.
Unless you sell your astrophotos as very large prints, I’d say don’t worry. In comparisons with the 30-megapixel Ra I found it difficult to see a difference in resolution between the two cameras. Stars were nearly as well resolved in the R6, and only under the highest pixel-peeping magnification did stars look a bit more pixelated in the R6 than in the Ra. Faint stars were equally well recorded.
The difference between 20 and 30 megapixels is not as great as you might think for arc-second-per-pixel plate scale. I think it would take going to the R5 with its 45 megapixel sensor to provide enough of a difference in resolution over the R6 to be obvious in nightscape scenes, or when shooting small, detailed deep-sky subjects such as globular clusters.
If landscape or wildlife photography by day is your passion, with astrophotography a secondary purpose, then the more costly but highly regarded R5 might be the better choice.
TIP: Adobe now offers (in Lightroom and in Camera Raw) a Super Resolution option, that users might think (judging by the rave reviews on-line) would be the answer to adding resolution to astro images from “low-res” cameras like the R6.
Sorry! In my tests on astrophotos I’ve found Super Resolution results unsatisfactory. Yes, stars were less pixelated, but they became oddly coloured in the AI-driven up-scaling. Green stars appeared! The sky background also became mottled and uneven.
I would not count on such “smart upscaling” options to add more pixels to astro-images from the R6. Then again, I don’t think there’s a need to.
RAW vs. cRAW
Canon now offers the option of shooting either RAW or cRAW files, the latter being the same megapixel count but compressed in file size by almost a factor of two. This allows shooting twice as many images before card space runs out, perhaps useful for shooting lots of time-lapses on extended trips away from a computer.
However, the compression is not lossless. In high-ISO test images purposely underexposed, then brightened in post, I could see a slight degradation in cRAW images – the noise background looked less uniform and exhibited a blocky look, like JPG artifacts.
TIP: With two SD card slots in the R6 (the second card can be set to record either a backup of images on card one, or serve as an overflow card) and the economy of large SD cards, there’s not the need to conserve card space as there once was. I would suggest always shooting in the full RAW format. Why accept any compression and loss of image quality?
The R6 uses a new version of Canon’s standard LP-E6 battery, the LP-E6NH, that supports charging through the USB-C port and has a higher 2130mAh capacity than the 1800mAh LP-E6 batteries. However, the R6 is compatible with older batteries.
On warm nights, I found the R6 ran fine on one battery for the 3 to 4 hours needed to shoot a time-lapse sequence, with power to spare. However, as noted below, the lack of a top LCD screen means there’s no ongoing display of battery level, a deficiency for time-lapse and deep-sky work.
For demanding applications, especially in winter, the R6 can be powered by an outboard USB power bank that has “Power Delivery” capability. That’s a handy feature. There’s no need to install a dummy battery leading out to a specialized power source.
TIP: Putting the camera into Airplane mode (to turn off WiFi and Bluetooth), turning off the viewfinder, and either switching off or closing the rear screen all helps conserve power. The R6 does not have GPS built in. Tagging images with location data requires connecting to your phone.
A major selling point for me was the R6’s low-light video capability. It replaces my Sony A7III, which had been my “go to” camera for real-time 4K movies of auroras.
As best I can tell (from the dimmer auroras I’ve shot to date), the R6 performs equally as well as the Sony. It is able to record good quality (i.e. acceptably noise-free) 4K movies at ISO 25,600 to ISO 51,200. While it can shoot at up to ISO 204,800, the excessive noise makes the top ISO an emergency-use only setting.
The R6 can shoot at a dragged shutter speed as slow as 1/8-second – good, though not as slow as the Sony’s 1/4-second slowest shutter speed in movie mode. That 1/8-second shutter speed and a fast f/1.4 to f/2 lens are the keys to shooting movies of the night sky. Only when auroras get shadow-casting bright can we shoot at the normal 1/30-second shutter speed and at lower ISOs.
As with Nikons (but not Sonys), the Canon R6 saves its movie settings separately from its still settings. When switching to Movie mode you don’t have to re-adjust the ISO, for example, to set it higher than it might have been for stills, very handy for taking both stills and movies of an active aurora, where quick switching is often required.
Unlike the R and Rp, the R6 captures 4K movies from the full width of the sensor, preserving the field of view of wide-angle lenses. This is excellent for aurora shooting.
However, the R6 offers the option of a “Movie Crop” mode. Rather than taking the 4K movie downsampled from the entire sensor, this crop mode records from a central 1:1 sampled area of the sensor. That mode can be useful for high-magnification lunar and planetary imaging, for ensuring no loss of resolution. It worked well, producing videos with less pixelated fine details in test movies of the Moon.
Though of course I have yet to test it on one, the R6 should be excellent for movies of total solar eclipses. It can shoot 4K up to 60 frames per second in both full frame and cropped frame. It cannot shoot 6K (buy the R3!) or 8K (buy the R5!).
Shooting in the R6’s Canon cLog3 profile records internally in 10-bit, preserving more dynamic range in movies, up to 12 stops. During eclipses, that will be a benefit for recording totality, with the vast range of brightness in the Sun’s corona. It should also aid in shooting auroras which can vary over a huge range in brightness.
TIP: Processing cLog movies, which look flat out of camera, requires applying a cLog3 Look Up Table, or LUT, to the movie clips in editing, a step called “colour grading.” This is available from Canon, from third-party vendors or, as it was with my copy of Final Cut Pro, might be already installed in your video editing software. When shooting, turn on View Assist so the preview looks close to what the final graded movie will look like.
EXPOSURE TRACKING IN TIME-LAPSES
In one test, I shot a time-lapse from twilight to darkness with the R6 in Aperture Priority auto-exposure mode, of a fading display of noctilucent clouds. I just let the camera lengthen the shutter speed on its own. It tracked the darkening sky very well, right down to the camera’s maximum exposure time of 30 seconds, using a fish-eye lens at f/2.8. This demonstrated that the light meter in the R6 was sensitive enough to work well in dim light.
Other cameras I have used cannot do this. The meter fails at some point and the exposure stalls at 5 or 6 seconds long, resulting in most frames after that being underexposed. By contrast, the R6 showed excellent performance, negating the need for special bulb ramping intervalometers for some “holy grail” scenes. Here’s the resulting movie.
In addition, the R6’s exposure meter tracked the darkening sky superbly, with nary a flicker or variation. Again, few cameras can do this. Nikons have an Exposure Smoothing option in their Interval Timers which works well.
The R6 has no such option but doesn’t seem to need it. The exposure did fail at the very end, when the shutter reached its maximum of 30 seconds. If I had the camera on Auto ISO, it might have started to ramp up the ISO to compensate, a test I have yet to try. Even so, this is impressive time-lapse performance in auto-exposure.
The R6, like the low-end Rp, lacks a top LCD screen for display of camera settings and battery level. In its place we get a traditional Mode dial, which some daytime photographers will prefer. But for astrophotography, a backlit top LCD screen provides useful information during long exposures.
Without it, the R6 provides no indication of battery level while a shoot is in progress, for example, during a time-lapse. A top screen is also useful for checking ISO and other settings by looking down at the camera, as is usually the case when it’s on a tripod or telescope.
The lack of a top screen is an inconvenience for astrophotography. We are forced to rely on looking at the brighter rear screen for all information. It is a flip-out screen, so can be angled up for convenient viewing on a telescope.
The R6 has a remote shutter port for an external intervalometer, or control via a time-lapse motion controller. That’s good!
However, the port is Canon’s low-grade 2.5mm jack. It works, and is a standard connector, but is not as sturdy as the three-pronged N3-style jack used on Canon’s 5D and 6D DSLRs, and on the R3 and R5. Considering the cost of the R6, I would have expected a better, more durable port. The On/Off switch also seems a bit flimsy and easily breakable under hard use.
These deficiencies provide the impression of Canon unnecessarily “cheaping out” on the R6. You can forgive them with the Rp, but not with a semi-professional camera like the R6.
Unlike the Canon R and Ra (which still mysteriously lack a built-in interval timer, despite firmware updates), the R6 has one in its firmware. Hurray! This can be used to set up a time-lapse sequence, but on exposures only up to the maximum of 30 seconds allowed by the camera’s shutter speed settings, true of most in-camera intervalometers.
For 30-second exposures taken in succession as quickly as possible the interval on the R6 has to be set to 34 seconds. The reason is that the 30-second exposure is actually 32 seconds, true of all cameras. With the R6, having a minimum gap in time between shots requires an Interval not of 33 seconds as with some cameras, but 34 seconds. Until you realize this, setting the intervalometer correctly can be confusing.
Like all Canon cameras, the R6 can be set to take only up to 99 frames, not 999. That seems a dumb deficiency. Almost all time-lapse sequences require at least 200 to 300 frames. What could it possibly take in the firmware to add an extra digit to the menu box? It’s there at in the Time-lapse Movie function that assembles a movie in camera, but not here where the camera shoots and saves individual frames. It’s another example where you just can’t fathom Canon’s software decisions.
TIP: If you want to shoot 100 or more frames, set the Number of Frames to 00, so it will shoot until you tell the camera to stop. But awkwardly, Canon says the way to stop an interval shoot is to turn off the camera! That’s crude, as doing so can force you to refocus if you are using a Canon RF lens. Switching the Mode dial to Bulb will stop an interval shoot, an undocumented feature.
As with most recent Canon DSLRs and DSLMs, the menu also includes a Bulb Timer. This allows setting an exposure of any length (many minutes or hours) when the camera is in Bulb mode. This is handy for single long shots at night.
However, it cannot be used in conjunction with the Interval Timer to program a series of multi-minute exposures, a pity. Instead, a separate outboard intervalometer has to be used for taking an automatic set of any exposures longer than 30 seconds, true of all Canons.
In Bulb and Bulb Timer mode, the R6’s rear screen lights up with a bright Timer readout. While the information is useful, the display is too bright at night and cannot be dimmed, nor turned red for night use, exactly when you are likely to use Bulb. The power-saving Eco mode has no effect on this display, precisely when you would want it to dim or turn off displays to prolong battery life, another odd deficiency in Canon’s firmware.
The Timer display can only be turned off by closing the flip-out screen, but now the viewfinder activates with the same display. Either way, a display is on draining power during long exposures. And the Timer readout lacks any indication of battery level, a vital piece of information during long shoots. The Canon R, R3 and R5, with their top LCD screens, do not have this annoying “feature.”
TIP: End a Bulb Timer shoot prematurely by hitting the Shutter button. That feature is documented.
IN-CAMERA IMAGE STACKING
The R6 offers a menu option present on many recent Canon cameras: Multiple Exposure. The camera can take and internally stack up to 9 images, stacking them by using either Average (best for reducing noise) or Bright mode (best for star trails). An Additive mode also works for star trails, but stacking 9 images requires reducing the exposure of each image by 3 stops, say from ISO 1600 to ISO 200, as I did in the example below.
The result of the internal stacking is a raw file, with the option of also saving the component raws. While the options work very well, in all the cameras I’ve owned that offer such functions, I’ve never used them. I prefer to do any stacking needed later at the computer.
TIP: The in-camera image stacking options are good for beginners wanting to get advanced stacking results with a minimum of processing fuss later. Use Average to stack ground images for smoother noise. Use Bright for stacking sky images for star trails. Activate one of those modes, then control the camera with a separate intervalometer to automatically shoot and internally stack several multi-minute exposures.
Being a mirrorless camera, there is no reflex mirror to introduce vibration, and so no need for a mirror lockup function. The shutter can operate purely mechanically, with physical metal curtains opening and closing to start and end the exposure.
However, the default “out of the box” setting is Electronic First Curtain, where the actual exposure, even when on Bulb, is initiated electronically, but ended by the mechanical shutter. That’s good for reducing vibration, perhaps when shooting the Moon or planets through a telescope at high magnification.
In Mechanical, the physical curtains both start and end the exposure. It’s the mode I usually prefer, as I like to hear the reassuring click of the shutter opening. I’ve never found shutter vibration a problem when shooting deep sky images on a telescope mount of any quality.
In Mechanical mode the shutter can fire at up to 12 frames a second, or up to 20 frames a second in Electronic mode where both the start and end of the exposure happen without the mechanical shutter. That makes for very quiet operation, good for weddings and golf tournaments!
Being vibration free, Electronic shutter might be great during total solar eclipses for rapid-fire bursts at second and third contacts when shooting through telescopes. Maximum exposure time is 1/2 second in this mode, more than long enough for capturing fleeting diamond rings.
Longer exposures needed for the corona will require Mechanical or Electronic First Curtain shutter. Combinations of shutter modes, drive rates (single or continuous), and exposure bracketing can all be programmed into the three Custom Function settings (C1, C2 and C3) on the Mode dial, for quick switching at an eclipse. It might not be until April 8, 2024 until I have a chance to test these features. And by then the R6 Mark II will be out!
TIP: While the R6’s manual doesn’t state it, some reviews mention (including at DPReview) that when the shutter is in fully Electronic mode the R6’s image quality drops from 14-bit to 12-bit, true of most other mirrorless cameras. This reduces dynamic range. I would suggest not using Electronic shutter for most astrophotography, even for exposures under 1/2 second. For longer exposures, it’s a moot point as it cannot be used.
TIP: The R6 has the same odd menu item that befuddles many a new R-series owner, found on Camera Settings: Page 4. “Release Shutter w/o Lens” defaults to OFF, which means the camera will not work if it is attached to a manual lens or telescope it cannot connect to electronically. Turn it ON and all will be solved. This is a troublesome menu option that Canon should eliminate or default to ON.
OTHER MENU FEATURES
The rear screen is fully touch sensitive, allowing all settings to be changed on-screen if desired, as well as by scrolling with the joystick and scroll wheels. I find going back to an older camera without a touchscreen annoying – I keep tapping the screen expecting it to do something!
The little Multi-Function (M-Fn) button is a worth getting used to, as it allows quick access to a choice of five important functions such as ISO, drive mode and exposure compensation. However, the ISO, aperture and shutter speed are all changeable by the three scroll wheels.
There’s also the Quick menu activated by the Q button. While the content of the Quick menu screen can’t be edited, it does contain a good array of useful functions, adjustable with a few taps.
Unlike Sonys, the R6 has no dedicated Custom buttons per se. However, it does offer a good degree of customization of its buttons, by allowing users to re-assign them to other functions they might find more useful than the defaults. For example ….
I’ve taken the AF Point button and assigned it to the Maximize Screen Brightness function, to temporarily boost the rear screen to full brightness for ease of framing.
The AE Lock button I assigned to switch the Focus Peaking indicators on and off, to aid manual focusing when needed.
The Depth of Field Preview button I assigned to switching between the rear screen and viewfinder, through that switch does happen automatically as you put your eye to the viewfinder.
The Set button I assigned to turning off the Rear Display, though that doesn’t have any effect when the Bulb Timer readout is running, a nuisance.
While the physical buttons are not illuminated, having a touch screen makes it less necessary to access buttons in the dark. It’s a pity the conveniently positioned but mostly unused Rate button can’t be re-programmed to more useful functions. It’s a waste of a button.
TIP: The shooting screens, accessed by the Info button (one you do need to find in the dark!), can be customized to show a little, a lot, or no information, as you prefer. Take the time to set them up to show just the information you need over a minimum of screen pages.
LENS AND FILTER COMPATIBILITY
The new wider RF mount accepts only Canon and third-party RF lenses. However, all Canon and third-party EF mount lenses (those made for DSLRs) will fit on RF-mount bodies with the aid of the $100 Canon EF-to-RF lens adapter.
This adapter will be necessary to attach any Canon R camera to a telescope equipped with a standard Canon T-ring. That’s especially true for telescopes with field flatterers where maintaining the standard 55mm distance between the flattener and sensor is critical for optimum optical performance.
The shallower “flange distance” between lens and sensor in all mirrorless cameras means an additional adapter is needed not just for the mechanical connection to the new style of lens mount, but also for the correct scope-to-sensor spacing.
The extra spacing provided by a mirrorless camera has the benefit of allowing a filter drawer to be inserted into the light path. Canon offers a $300 lens adapter with slide-in filters, though the choice of filters useful for astronomy that fit Canon’s adapter is limited. AstroHutech offers a few IDAS nebula filters.
Clip-in filters made for the EOS R, such as those offered by Astronomik, will also fit the R6. Though, again, most narrowband filters will not work well with an unmodified camera.
TIP: Alternatively, AstroHutech also offers its own lens adapter/filter drawer that goes from a Canon EF mount to the RF mount, and accepts standard 52mm or 48mm filters. It is a great way to add interchangeable filters to any telescope when using an R-series camera, while maintaining the correct back-focus spacing. I use an AstroHutech drawer with my Ra, where the modified camera works very well with narrowband filters. Using such filters with a stock R6 won’t be as worthwhile, as I showed above.
As of this writing, the selection of third-party lenses for the Canon RF mount is limited, as neither Canon or Nikon have “opened up” their system to other lens makers, unlike Sony with their E-mount system. For example, we have yet to see much-anticipated RF-mount lenses from Sigma, Tamron and Tokina.
The few third-party lenses that are available, from TTArtisan, Venus Optics and other boutique Chinese lens companies, are usually manual focus lenses with reverse-engineered RF mounts offering no electrical contact with the camera. Some of these wide-angle lenses are quite good and affordable. (I tested the TTArtisan 11mm fish-eye here.)
Until other lens makers are “allowed in,” if you want lenses with auto-focus and camera metadata connections, you almost have to buy Canon. Their RF lenses are superb, surpassing the quality of their older EF-mount equivalents. But they are costly. I sold off a lot of my older lenses and cameras to help pay for the new Canon glass!
Astrophotographers often like to operate their cameras at the telescope using computers running specialized control software. I tested the R6 with two popular Windows programs for controlling DSLR and now mirrorless cameras, BackyardEOS (v3.2.2) and AstroPhotographyTool (v3.88). Both recognized and connected to the R6 via its USB port.
Another popular option is the ASIair WiFi controller from ZWO. It controls cameras via one of the ASIair’s USB ports, and not (confusingly) through the Air’s remote shutter jack marked DSLR. Under version 1.7 of its mobile app, the ASIair now controls Canon R cameras and connected to the R6 just fine, allowing images to be saved both to the camera and to the Air’s own MicroSD card.
The ASIair is an excellent solution for both camera control and autoguiding, with operation via a mobile device that is easier to use and power in the field than a laptop. I’ve not tried other hardware and software controllers with the R6.
TIP: While the R6, like many Canon cameras, can be controlled remotely with a smartphone via the CanonConnect mobile app, the connection process is complex and the connection can be unreliable. The Canon app offers no redeeming features for astrophotography, and maintaining the connection via WiFi or Bluetooth consumes battery power.
SUGGESTIONS TO CANON
To summarize, in firmware updates, Canon should:
Fix the low-level amp glow. No camera should have amp glow.
Allow either dimming the Timer readout, turning it red, or just turning it off!
Add a battery display to the Timer readout.
Expand the Interval Timer to allow up to 999 frames, as in the Time-Lapse Movie.
Allow the Rate button to be re-assigned to more functions.
Default the Release Shutter w/o Lens function to ON.
Revise the manual to correctly describe how to stop an Interval Timer shoot.
Allow programming multiple long exposures by combining Interval and Bulb Timer, or by expanding the shutter speed range to longer than 30 seconds, as some Nikons can do.
The extended red sensitivity of the Canon EOS Ra makes it better suited for deep-sky imaging. But with it now out of production (Canon traditionally never kept its astronomical “a” cameras in production for more than two years), I think the R6 is now Canon’s best camera (mirrorless or DSLR) for all types of astrophotography, both stills and movies.
However, I cannot say how well it will work when filter-modified by a third-party. But such a modification is necessary only for recording red nebulas in the Milky Way. It is not needed for other celestial targets and forms of astrophotography.
The low noise and ISO invariant sensor of the R6 makes it superb for nightscapes, apart from the nagging amp glow. That glow will also add an annoying edge gradient to deep-sky images, best dealt with when shooting by the use of LENR or dark frames.
As the image of the Andromeda Galaxy, M31, at the top of the blog attests, with careful processing it is certainly possible to get fine deep-sky images with the R6.
For low-light movies the R6 is Canon’s answer to the Sony alphas. No other Canon camera can do night sky movies as well as the R6. For me, it was the prime feature that made the R6 the camera of choice to complement the Ra.
The tradition continued of chasing clear skies to see a lunar eclipse.
It wouldn’t be an eclipse without a chase. Total eclipses of the Sun almost always demand travel, often to the far side of the world, to stand in the narrow path of the Moon’s shadow.
By contrast, total eclipses of the Moon come to you — they can be seen from half the planet when the Full Moon glides through Earth’s shadow.
Assuming you have clear skies! That’s the challenge.
Of the 14 total lunar eclipses (TLEs) visible from here in Alberta since 2000, I have seen all but one, missing the January 21, 2000 TLE due to clouds.
But of the remaining 13 TLEs so far in the 21st century, I watched only three from home, the last home lunar eclipse being in December 2010.
I viewed three TLEs (August 2007, February 2008, and December 2011) from the Rothney Observatory south-west of Calgary as part of public outreach programs I was helping with.
In April 2014, I was in Australia and viewed the eclipsed Moon rising in the evening sky over Lake Macquarie, NSW.
A year later, in April 2015, I was in Monument Valley, on the Arizona-Utah border for the short total eclipse of the Moon at dawn.
But of the eclipses I’ve seen from Alberta since 2014, I have had to chase into clear skies for all of them — to Writing-on-Stone Provincial Park in both October 2014 and September 2015, to the Crowsnest Pass for January 2018, and to Lloydminster for January 2019.
The total lunar eclipse on the morning of May 26, 2021 was no exception.
Leading up to eclipse day prospects for finding clear skies anywhere near home in southern Alberta looked bleak. The province was under widespread cloud bringing much-needed rain. Good for farmers, but bad for eclipse chasers.
Then, two days prior to the eclipse a hole in the clouds was predicted to open up along the foothills in central Alberta just at the right time, at 4 a.m. The predictions stayed consistent a day later.
So trusting the Environment Canada models that had served me well since 2014, I made plans to drive north the day before the eclipse to Rocky Mountain House, a sizeable town on Highway 11 west of Red Deer, where the foothills begin. “Rocky” was predicted to be on the edge of the clearing, with a large swath of clear sky in the right direction, to the southwest where the Moon would be.
Fortunately, COVID restrictions are not so severe here as to demand stay-at-home orders. I could travel, at least within Alberta. Hotels were open, but restaurants only for takeaway.
This was going to be a tough eclipse even under the best of sky conditions, as for us in Alberta the Moon would be low and setting into the southwest at dawn. The Moon would be darkest and in mid-eclipse just as the sky was also brightening with dawn twilight.
However, a low eclipse offers the opportunity of a view of the reddened Moon over a scenic landscape, in this case of the eclipsed Moon setting over the Rockies. That was the plan.
Unfortunately, Rocky Mountain House wasn’t the ideal destination as it lies far from the mountains. I was hoping for a site closer to the Rockies in southern Alberta. But a site with clear skies is always the first priority.
The task is then finding a spot to set up with a clear view to the southwest horizon, which from the area around Rocky is tough — it’s all trees!
This is where planning apps are wonderful.
I used The Photographer’s Ephemeris (TPE) to search for a side road or spot to pull off where I could safely set up and be away from trees to get a good sightline to the horizon and possibly distant mountains.
A site not far from town was ideal, to avoid long pre- and post-eclipse drives in the wee hours of the morning. The timing of this eclipse was part of the challenge — in having to be on site at 4 a.m.
TPE showed several possible locations and a Google street view (not shown here) seemed to confirm that the horizon in that area off Highway 11 would be unobstructed over cultivated fields.
But you don’t know for sure until you get there.
So as soon as I arrived, I went to one site I had found remotely, only to discover power lines in the way. Not ideal.
I found another nearby side road with a clean view. From there I used the PhotoPills app (above) and its augmented reality “AR” mode to confirm, that yes, the Moon would be in the right place over a clear horizon at eclipse time the next morning.
Another app I like for site scouting, Theodolite, also confirmed that the view toward the eclipsed Moon’s direction (with an azimuth of about 220°) would be fine from that site.
As a Plan B — it’s always good to have a Plan B! — I also drove west along Highway 11, the David Thompson Highway, toward the mountains, in search of a rare site away from trees, just in case the only clear skies lay to the west. I found one, some 50 km west of Rocky, but thankfully it was not needed. The Plan A site worked fine, and was just 5 minutes south of town, and bed!
I set up two tripods. One was for the Canon R6 with an 85mm lens for a “time-lapse” sequence of the Moon moving across the frame as it entered the Earth’s umbral shadow.
The other tripod I used for closeups of just the Moon using the Canon 60Da and 200mm lens, then switched to the Canon Ra and a 135mm lens, then the longer 200mm lens once the Moon got low enough to also be in frame with the horizon. Those were for the prime shot of the eclipse over the distant mountains and skyline.
It all worked! The sky turned out to be clearer than predicted, a pleasant surprise, with only some light cloud obscuring the Moon halfway through the partial phases (the first image at top).
The other surprise was how dark the shadowed portion of the Moon was. This was a very short total eclipse, with totality only 14 minutes long. With the Moon passing through the outer, lighter part of the umbral shadow, I would have expected a brighter eclipse, making the reddened Moon stand out better in the blue twilight.
As it was, in the minutes before the official start of totality at 5:11 a.m. MDT, the Moon effectively disappeared from view, both to the eye and camera.
My best shots were of the Moon still in partial eclipse but with the umbral shaded portion bright enough to show up red in the images. The distant Rockies were also beginning to light up pink in the first light of dawn.
My last view was of a sliver-thin Moon disappearing into Earth’s shadow just prior to the onset of totality. I packed up and headed back to bed with technically the Moon still up and in total eclipse, but impossible to see. Still I was a happy eclipse chaser!
It was another successful eclipse trip, thwarted not so much by clouds, but by the darkness of our planet’s shadow, which might have been due to widespread cloud or volcanic ash in the atmosphere of Earth.
The other factor at play was that this was a “supermoon,” with the larger Moon near perigee entering more deeply into the umbra than a normal-sized Moon.
The next lunar eclipse is six months later, on the night of November 18/19, 2021 when the Moon will not quite fully enter Earth’s umbral shadow, for a 97% partial eclipse. But enough of the Moon will be in the dark umbra for most of the Moon to appear red, with a white crescent “smile” at the bottom.
As shown above, from my location in Alberta the Moon will appear high in the south, in Taurus just west of the Milky Way. The winter stars and Milky Way will “turn on” and fade into view as the eclipse progresses.
We shall see if that will be a rare “home” eclipse, or if it will demand another chase to a clear hole in the clouds on a chilly November night.
I present my top 10 tips for capturing time-lapses of the moving sky.
If you can take one well-exposed image of a nightscape, you can take 300. There’s little extra work required, just your time. But if you have the patience, the result can be an impressive time-lapse movie of the night sky sweeping over a scenic landscape. It’s that simple.
Or is it?
Here are my tips for taking time-lapses, in a series of “Do’s” and “Don’ts” that I’ve found effective for ensuring great results.
But before you attempt a time-lapse, be sure you can first capture well-exposed and sharply focused still shots. Shooting hundreds of frames for a time-lapse will be a disappointing waste of your time if all the images are dark and blurry.
For that reason many of my tips apply equally well to shooting still images. But taking time-lapses does require some specialized gear, techniques, planning, and software. First, the equipment.
NOTE: This article appeared originally in Issue #9 of Dark Sky Travels e-magazine.
TIP 1 — DO: Use a solid tripod
A lightweight travel tripod that might suffice for still images on the road will likely be insufficient for time-lapses. Not only does the camera have to remain rock steady for the length of the exposure, it has to do so for the length of the entire shoot, which could be several hours. Wind can’t move it, nor any camera handling you might need to do mid-shoot, such as swapping out a battery.
The tripod needn’t be massive. For hiking into scenic sites you’ll want a lightweight but sturdy tripod. While a carbon fibre unit is costly, you’ll appreciate its low weight and good strength every night in the field. Similarly, don’t scrimp on the tripod head.
TIP 2 — DO: Use a fast lens
As with nightscape stills, the single best purchase you can make to improve your images of dark sky scenes is not buying a new camera (at least not at first), but buying a fast, wide-angle lens.
Ditch the slow kit zoom and go for at least an f/2.8, if not f/2, lens with 10mm to 24mm focal length. This becomes especially critical for time-lapses, as the fast aperture allows using short shutter speeds, which in turn allows capturing more frames in a given period of time. That makes for a smoother, slower time-lapse, and a shoot you can finish sooner if desired.
TIP 3 — DO: Use an intervalometer
Time-lapses demand the use of an intervalometer to automatically fire the shutter for at least 200 to 300 images for a typical time-lapse. Many cameras have an intervalometer function built into their firmware. The shutter speed is set by using the camera in Manual mode.
Just be aware that a camera’s 15-second exposure really lasts 16 seconds, while a 30-second shot set in Manual is really a 32-second exposure.
So in setting the interval to provide one second between shots, as I advise below, you have to set the camera’s internal intervalometer for an interval of 17 seconds (for a shutter speed of 15 seconds) or 33 seconds (for a shutter speed of 30 seconds). It’s an odd quirk I’ve found true of every brand of camera I use or have tested.
Alternatively, you can set the camera to Bulb and then use an outboard hardware intervalometer (they sell for $60 on up) to control the exposure and fire the shutter. Test your unit. Its interval might need to be set to only one second, or to the exposure time + one second.
How intervalometers define “Interval” varies annoyingly from brand to brand. Setting the interval incorrectly can result in every other frame being missed and a ruined sequence.
SETTING YOUR CAMERA
TIP 4 — DON’T: Underexpose
As with still images, the best way to beat noise is to give the camera signal. Use a wider aperture, a longer shutter speed, or a higher ISO (or all of the above) to ensure the image is well exposed with a histogram pushed to the right.
If you try to boost the image brightness later in processing you’ll introduce not only the very noise you were trying to avoid, but also odd artifacts in the shadows such as banding and purple discolouration.
With still images we have the option of taking shorter, untrailed images for the sky, and longer exposures for the dark ground to reveal details in the landscape, to composite later. With time-lapses we don’t have that luxury. Each and every frame has to capture the entire scene well.
At dark sky sites, expose for the dark ground as much as you can, even if that makes the sky overly bright. Unless you outright clip the highlights in the Milky Way or in light polluted horizon glows, you’ll be able to recover highlight details later in processing.
After poor focus, underexposure, resulting in overly noisy images, is the single biggest mistake I see beginners make.
TIP 5 — DON’T: Worry about 500 or “NPF” Exposure Rules
While still images might have to adhere to the “500 Rule” or the stricter “NPF Rule” to avoid star trailing, time-lapses are not so critical. Slight trailing of stars in each frame won’t be noticeable in the final movie when the stars are moving anyway.
So go for rule-breaking, longer exposures if needed, for example if the aperture needs to be stopped down for increased depth of field and foreground focus. Again, with time-lapses we can’t shoot separate exposures for focus stacking later.
Just be aware that the longer each exposure is, the longer it will take to shoot 300 of them.
Why 300? I find 300 frames is a good number to aim for. When assembled into a movie at 30 frames per second (a typical frame rate) your 300-frame clip will last 10 seconds, a decent length of time in a final movie.
You can use a slower frame rate (24 fps works fine), but below 24 the movie will look jerky unless you employ advanced frame blending techniques. I do that for auroras.
How long it will take to acquire the needed 300 frames will depend on how long each exposure is and the interval between them. An app such as PhotoPills (via its Time lapse function) is handy in the field for calculating exposure time vs. frame count vs. shoot length, and providing a timer to let you know when the shoot is done.
TIP 6 — DO: Use short intervals
At night, the interval between exposures should be no more than one or two seconds. By “interval,” I mean the time between when the shutter closes and when it opens again for the next frame.
Not all intervalometers define “Interval” that way. But it’s what you expect it means. If you use too long an interval then the stars will appear to jump across the sky, ruining the smooth motion you are after.
In practice, intervals of four to five seconds are sometimes needed to accommodate the movement of motorized “motion control” devices that turn or slide the camera between each shot. But I’m not covering the use of those advanced units here. I cover those options and much, much more in 400 pages of tips, techniques and tutorials in my Nightscapes ebook, linked to above.
However, during the day or in twilight, intervals can be, and indeed need to be, much longer than the exposures. It’s at night with stars in the sky that you want the shutter to be closed as little as possible.
TIP 7 — DO: Shoot Raw
This advice also applies to still images where shooting raw files is essential for professional results. But you likely knew that.
However, with time-lapses some cameras offer a mode that will shoot time-lapse frames and assemble them into a movie right in the camera. Don’t use it. It gives you a finished, pre-baked movie with no ability to process each frame later, an essential step for good night time-lapses. And raw files provide the most data to work with.
So even with time-lapses, shoot raw not JPGs.
If you are confident the frames will be used only for a time-lapse, you might choose to shoot in a smaller S-Raw or compressed C-Raw mode, for smaller files, in order to fit more frames onto a card.
But I prefer not to shrink or compress the original raw files in the camera, as some of them might make for an excellent stacked and layered still image where I want the best quality originals (such as for the ISS over Waterton Lakes example above).
To get you through a long field shoot away from your computer buy more and larger memory cards. You don’t need costly, superfast cards for most time-lapse work.
PLANNING AND COMPOSITION
TIP 8 — DO: Use planning apps to frame
All nightscape photography benefits from using one of the excellent apps we now have to assist us in planning a shoot. They are particularly useful for time-lapses.
Apps such as PhotoPills and The Photographer’s Ephemeris are great. I like the latter as it links to its companion TPE 3D app to preview what the sky and lighting will look like over the actual topographic horizon from your site. You can scrub through time to see the motion of the Milky Way over the scenery. The Augmented Reality “AR” modes of these apps are also useful, but only once you are on site during the day.
For planning a time-lapse at home I always turn to a “planetarium” program to simulate the motion of the sky (albeit over a generic landscape), with the ability to add in “field of view” indicators to show the view your lens will capture.
You can step ahead in time to see how the sky will move across your camera frame during the length of the shoot. Indeed, such simulations help you plan how long the shoot needs to last until, for example, the galactic core or Orion sets.
Planetarium software helps ensure you frame the scene properly, not only for the beginning of the shoot (that’s easy — you can see that!), but also for the end of the shoot, which you can only predict.
If your shoot will last as long as three hours, do plan to check the battery level and swap batteries before three hours is up. Most cameras, even new mirrorless models, will now last for three hours on a full battery, but likely not any longer. If it’s a cold winter night, expect only one or two hours of life from a single battery.
TIP 9 — DO: Develop one raw frame and apply settings to all
Processing the raw files takes the same steps and settings as you would use to process still images.
With time-lapses, however, you have to do all the processing required within your favourite raw developer software. You can’t count on bringing multiple exposures into a layer-based processor such as Photoshop to stack and blend images. That works for a single image, but not for 300.
I use Adobe Camera Raw out of Adobe Bridge to do all my time-lapse processing. But many photographers use Lightroom, which offers all the same settings and non-destructive functions as Adobe Camera Raw.
For those who wish to “avoid Adobe” there are other choices, but for time-lapse work an essential feature is the ability to develop one frame, then copy and paste its settings (or “sync” settings) to all the other frames in the set.
Not all programs allow that. Affinity Photo does not. Luminar doesn’t do it very well. DxO PhotoLab, ON1 Photo RAW, and the free Raw Therapee, among others, all work fine.
HOW TO ASSEMBLE A TIME-LAPSE
Once you have a set of raws all developed, the usual workflow is to export all those frames out as high-quality JPGs which is what movie assembly programs need. Your raw developing software has to allow batch exporting to JPGs — most do.
However, none of the programs above (except Photoshop and Adobe’s After Effects) will create the final movie, whether it be from those JPGs or from the raws.
So for assembling the intermediate JPGs into a movie, I often use a low-cost program called TLDF (TimeLapse DeFlicker) available for MacOS and Windows (timelapsedeflicker.com). It offers advanced functions such as deflickering (i.e. smoothing slight frame-to-frame brightness fluctuations) and frame blending (useful to smooth aurora motions or to purposely add star trails).
While there are many choices for time-lapse assembly, I suggest using a program dedicated to the task and not, as many do, a movie editing program. For most sequences, the latter makes assembly unnecessarily difficult and harder to set key parameters such as frame rates.
TIP 10 — DO: Try LRTimelapse for more advanced processing
Get serious about time-lapse shooting and you will want — indeed, you will need — the program LRTimelapse (LRTimelapse.com). A free but limited trial version is available.
This powerful program is for sequences where one setting will not work for all the frames. One size does not fit all.
Instead, LRTimelapse allows you to process a few keyframes throughout a sequence, say at the start, middle, and end. It then interpolates all the settings between those keyframes to automatically process the entire set of images to smooth (or “ramp”) and deflicker the transitions from frame to frame.
This is essential for sequences where the lighting changes during the shoot (say, the Moon rises or sets), and for so-called “holy grails.” Those are advanced sequences that track from daylight or twilight to darkness, or vice versa, over a wide range of camera settings.
However, LRTimelapse works only with Adobe Lightroom or the Adobe Camera Raw/Bridge combination. So for advanced time-lapse work Adobe software is essential.
A Final Bonus Tip
Keep it simple. You might aspire to emulate the advanced sequences you see on the web, where the camera pans and dollies during the movie. I suggest avoiding complex motion control gear at first to concentrate on getting well-exposed time-lapses with just a static camera. That alone is a rewarding achievement.
But before that, first learn to shoot still images successfully. All the settings and skills you need for a great looking still image are needed for a time-lapse. Then move onto capturing the moving sky.
I end with a link to an example music video, shot using the techniques I’ve outlined. Thanks for reading and watching. Clear skies!
The Beauty of the Milky Way from Alan Dyer on Vimeo.
I had the chance to test out an early sample of Canon’s new EOS Ra camera designed for deep-sky photography.
Once every 7 years astrophotographers have reason to celebrate when Canon introduces one of their “a” cameras, astronomical variants optimized for deep-sky objects, notably red nebulas.
In 2005 Canon introduced the ground-breaking 8-megapixel 20Da, the first DLSR to feature Live View for focusing. Seven years later, in 2012, Canon released the 18-megapixel 60Da, a camera I still use and love.
Both cameras were cropped-frame DSLRs.
Now in 2019, seven years after the 60Da, we have the newly-released EOS Ra, the astrophoto version of the 30-megapixel EOS R released in late 2018. The EOS R is a full-frame mirrorless camera with a sensor similar to what’s in Canon’s 5D MkIV DSLR.
Here, I present a selection of sample images taken with the new EOS Ra.
Both versions of the EOS R have identical functions and menus.
The big difference is that the EOS Ra, as did Canon’s earlier “a” models, has a factory-installed filter in front of the sensor that transmits more of the deep red “hydrogen-alpha” wavelength emitted by glowing nebulas.
Normal cameras suppress much of this deep-red light as a by-product of their filters cutting out the infra-red light that digital sensors are very sensitive to, but that would not focus well.
I was sent an early sample of the EOS Ra, and earlier this autumn also had a sample of the stock EOS R.
Both were sent for testing so I could prepare a test report for Sky and Telescope magazine. The full test report will appear in an upcoming issue.
• How the Ra compares to previous “a” models and third-party filter-modified cameras
• How the Ra works for normal daylight photography
• Noise levels compared to other cameras
• Features unique to the EOS Ra, such as 30x Live View focusing
UPDATE — November 25, 2019
As part of further testing I shot the Heart and Soul Nebulas in Cassiopeia through my little Borg 77mm f/4 astrograph with both the EOS Ra and my filter-modified 5D MkII (modified years ago by AstroHutech) to compare which pulled in more nebulosity. It looked like a draw.
Both images are single 8-minute exposures, taken minutes apart and developed identically in Adobe Camera Raw, but adjusted for colour balance to equally neutralize the sky background. The histograms look similar. Even so, the Ra looks a little redder overall. But keep in mind a sky or nebula can be made to appear any shade of red you like in processing.
The question is which camera shows more faint nebulosity?
The modified 5D MkII has always been my favourite camera for this type of astrophotography, picking up more nebulosity than other “a” models I’ve tested, including the Nikon D810a.
But in this case, I’d say the EOS Ra is performing as well as, if not better than the 5D MkII. How well any third-party modified camera you buy now performs will depend which, if any, filter the modifier installs in front of the sensor. So your mileage will vary.
For most of my other testing I shot through my much-prized Astro-Physics Traveler, a 105mm aperture f/6 apochromatic refractor on the Astro-Physics Mach1 mount.
To connect the EOS Ra (with its new RF lens mount) to my existing telescope-to-camera adapter and field flattener lens I used one of Canon’s EF-EOS R lens adapters.
The bottom line is that the EOS Ra works great!
It performs very well on H-alpha-rich nebulas and has very low noise. It will be well-suited to not only deep-sky photography but also to wide-field nightscape and time-lapse photography, perhaps as Canon’s best camera yet for those applications.
WHAT ABOUT THE PRICE?
The EOS Ra will sell for $2,500 US, a $700 premium over the cost of the stock EOS R. Some complain. Of course, if you don’t like it, you don’t have to buy it. This is not an upgrade being forced upon you.
As I look at it, it is all relative. When Nikon’s astronomy DSLR, the 36 Mp D810a, came out in 2015 it sold for $3,800 US, $1,300 more than the EOS Ra. It was, and remains a fine camera, if you can find one. It is discontinued.
A 36 Mp cooled and dedicated CMOS astro camera, the QHY367, with the same chip as the D810a, goes for $4,400, $1,900 more than the Ra. Yes, it will produce better images I’m sure than the EOS Ra, but deep-sky imaging is all it can do. At a cost, in dollars and ease of use.
And yes, buying a stock EOS R and having it modified by a third party costs less, and you’ll certainly get a good camera, for $300 to $400 less than an Ra. But …
• The EOS Ra has a factory adjusted white balance for ease of “normal” use — no need to buy correction filters. So there’s a $$ saving there, even if you can find clip-in correction filters for the EOS R — you can’t.
• And the Ra retains the sensor dust cleaning function. Camera modifier companies remove it or charge more to reinstall it.
• And the 30x live view magnification is very nice.
• The EOS Ra also carries a full factory warranty.
Do I wish the EOS Ra had some other key features? Sure. A mode to turn all menus red would be nice. As would an intervalometer built-in, one that works with the Bulb Timer to allow sequences of programmed multi-minute exposures. Both could be added in with a firmware update.
And providing a basic EF-EOS R lens adapter in the price would be a welcome plus, as one is essential to use the EOS Ra on a telescope.
That’s my take on it. I’ll be buying one. But then again I bought the 20Da, twice!, and the 60Da, and I hate to think what I paid for those much less capable cameras.
BONUS TEST — The RF 15-35mm L Lens
Canon is also releasing an impressive series of top-class RF lenses for their R mirrorless cameras. The image below is an example astrophoto with the new RF 15-35mm f/2.8 L zoom lens, an ideal combination of focal lengths and speed for nightscape shooting.
Below is a further set of stacked and processed images with the RF 15-35mm L lens, taken in quick succession, at 15mm, 24mm, and 35mm focal lengths, all shot wide open at f/2.8. The EOS Ra was on the Star Adventurer tracker (as below) to follow the stars.
Click or tap on the images below to view a full-resolution version for closer inspection.
The RF 15-35mm lens performs extremely well at 15mm exhibiting very little off-axis aberrations at the corners.
Off-axis aberrations do increase at the longer focal lengths but are still very well controlled, and are much less than I’ve seen on my older zoom and prime lenses in this focal length range.
The RF 15-35mm is a great complement to the EOS Ra for wide-field Milky Way images.
I was impressed with the new EOS Ra. It performs superbly for astrophotography.
In a technical blog I compare the new Canon 6D Mark II camera with its predecessor, the Canon 6D, with the focus on performance for nightscape astrophotography.
No pretty pictures in this blog I’m afraid! This is a blog for gear geeks.
The long-awaited Canon 6D Mark II camera is out, replacing the original 6D after that camera’s popular 5-year reign as a prime choice among astrophotographers for all kinds of sky images, including nightscapes and time-lapses.
As all new cameras do, the 6D Mark II is currently fetching a full list price of $2000 U.S. Eventually it will sell for less. The original 6D, introduced in 2012 at that same list price, might still be available from many outlets, but for less, likely below $1500 US.
Shown on the left, above, the 6D Mark II is similar in size and weight to the original 6D.
However, the new Mark II offers 6240 x 4160 pixels for 26 megapixels, a bump up in resolution over the 5472 x 3648 20-megapixel 6D. The pixel pitch of the Mark II sensor is 5.7 microns vs. 6.6 microns for the 6D.
One difference is that the port for a remote release is now on the front, but using the same solid 3-pin N3 connector as the 6D and other full-frame Canons. That makes it compatible with all external controllers for time-lapse shooting.
TESTING FOR THE NIGHT
My interest is in a camera’s performance for long-exposure astrophotography, with images taken at high ISO settings. I have no interest in auto-focus performance (we shoot at night with focus set manually), nor how well a camera works for high-speed sports shooting.
To test the Mark II against the original 6D I took test shots at the same time of a high-contrast moonlit scene in the backyard, using a range of ISO speeds typical of nightscape scenes.
The comparisons show close-ups of a scene shown in full in the smaller inset screen.
The key characteristic of interest for night work is noise. How well does the camera suppress the noise inherent in digital images when the signal is boosted to the high ISO settings we typically use?
This set shows the 6D MkII at five ISOs, from ISO 1600 all the way up to the seldom-used ISO 25,600, all shot in Raw, not JPG. In all cases, no noise reduction was applied in later processing, so the results do look worse than what processed images would.
Click or tap on all images to expand each image to full screen for closer inspection.
This set shows the same range of ISOs with the original 6D. All were taken at the same aperture, f/2.8, with a 35mm lens. Exposures were halved for each successive bump up in ISO speed, to ensure equally exposed images.
Comparing the sets, the 6D MkII shows a much greater tendency to exhibit a magenta cast in the shadows at very high ISOs, plus a lower contrast in the shadows at increasing ISOs, and slightly more luminance noise than the 6D.
How much more noise the 6D MkII exhibits is demonstrated here.
To me, visually, the MkII presents about 1/2 stop, or EV, worse noise than the 6D.
In this example, the MkII exhibits a noise level at ISO 3200 (a common nightscape setting) similar to what the 6D does if set between ISO 4000 and 5000 – about 1/2 stop worse noise.
Frankly, this is surprising.
Yes, the MkII has a higher pixel count and therefore smaller pixels (5.7 microns in this case) that are always more prone to noise. But in the past, advances to the in-camera signal processing has prevented noise from becoming worse, despite increasing pixel count, or has even produced an improvement in noise.
For example, the 2012-vintage 6D is better for noise than Canon’s earlier 2008-era 5D MkII model by about half a stop, or EV.
After five years of camera development I would have expected a similar improvement in the 6D MkII. After all, the 6D MkII has Canon’s latest DIGIC 7 processor, vs. the older 6D’s DIGIC 5+.
Instead, not only is there no noise improvement, the performance is worse.
That said, noise performance in the 6D MkII is still very good, and better than you’ll get with today’s 24 megapixel cropped-frame cameras with their even smaller 4 micron pixels. But the full frame 6D MkII doesn’t offer quite as much an improvement over cropped-frame cameras as does the five-year-old 6D.
In the previous sets all the images were well-exposed, as best they could be for such a contrasty scene captured with a single exposure.
What happens when Raw images are underexposed, then boosted later in exposure value in processing?
This is not an academic question, as that’s often the reality for nightscape images where the foreground remains dark. Bringing out detail in the shadows later requires a lot of Shadow Recovery or increasing the Exposure. How well will the image withstand that work on the shadows?
To test this, I shot a set of images at the same shutter speed, but at successively slower ISOs, from a well-exposed ISO 3200, to a severely underexposed ISO 100. I then boosted the Exposure setting later in Raw processing by an amount that compensated for the level of underexposure in the camera, from a setting of 0 EV at ISO 3200, to a +5 EV boost for the dark ISO 100 shots.
This tests for a camera’s “ISO Invariancy.” If a camera has a sensor and signal processing design that is ISO invariant, a boosted underexposed image at a slow ISO should look similar to a normally exposed image at a high ISO.
You’re just doing later in processing what a camera does on its own in-camera when bumping up the ISO.
But cameras that use ISO “variant” designs suffer from increased noise and artifacts when severely underexposed images are boosted later in Raw processing.
The Canon 6D and 6D MkII are such cameras.
This set above shows the results from the 6D Mark II. Boosting underexposed shadows reveals a lot of noise and a severe magenta cast.
These are all processed with Adobe Camera Raw, identical to the development engine in Adobe Lightroom.
This set above shows the results from the 6D. The older camera, which was never great for its lack of ISO Invariancy performance, is still much better than the new Mark II.
Effectively, this is the lack of dynamic range that others are reporting when testing the 6D MkII on more normal daytime images. It really rears its ugly head in nightscapes.
The lesson here is that the Mark II needs to be properly exposed as much as possible.
Don’t depend on being able to extract details later from the shadows. The adage “Expose to the Right,” which I explain at length in my Nightscapes eBook, applies in spades to the 6D MkII.
DARK FRAME BUFFER
All the above images were taken with Long Exposure Noise Reduction (LENR) off. This is the function that, when turned on, forces the camera to take and internally subtract a dark frame – an image of just the noise – reducing thermal noise and discolouration in the shadows.
A unique feature of Canon full-frame cameras is that when LENR is on you can take several exposures in quick succession before the dark frame kicks in and locks up the camera. This is extremely useful for deep-sky shooting.
The single dark frame then gets applied to the buffered “light frames.”
The 6D Mark II, when in either Raw or in Raw+JPG can take 3 shots in succession. This is a downgrade from the 6D which can take 4 shots when in Raw+JPG. Pity.
ADOBE CAMERA RAW vs. DIGITAL PHOTO PROFESSIONAL
My next thought was that Adobe Camera Raw, while it was reading the Mark II files fine, might not have been de-Bayering or developing them properly. So I developed the same image with both Raw developers, Adobe’s and Canon’s latest version of their own Digital Photo Professional (DPP).
Here I did apply a modest and approximately similar level of noise reduction to both images:
In ACR: Color at 25, Luminosity at 40, with Sharpness at 25
In DPP: Chrominance at 8, Luminosity at 8, with Sharpness at 2
Yes, DPP did do a better job at eliminating the ugly magenta cast, but did a much worse job at reducing overall noise. DPP shows a lot of blockiness, detail loss, and artifacts left by the noise reduction.
Adobe Camera Raw and/or Lightroom remain among the best of many Raw developers.
A new feature the 6D Mark II offers is the ability to shoot and stack images in-camera. It can either “Add” the exposure values, or, most usefully, “Average” them, as shown here.
Other newer Canon DSLRs also offer this feature, notably the 7D MkII, the 5D MkIV, the 5Ds, and even the entry-level 80D. So the 6D MkII is not unique. But the feature was not on the 6D.
Here’s the benefit.
The left image is a single exposure; the middle is an average stack of 4 exposures stacked in camera; the right image an average stack of 9 exposures, the maximum allowed.
Noise smooths out a lot, with less noise the more images you stack. The result is a single Raw file, not a JPG. Excellent!
While this kind of stacking can be done later in processing in Photoshop, or in any layer-based program, many people might find this in-camera function handy.
Except, as you can see, the sky will exhibit star trails, and not as well defined as you would get from stacking them with a “Lighten” blend mode, as all star trail stacking routines use.
So this averaging method is NOT the way to do star trails. The Mark II does not offer the Brighten mode some other new Canons have that does allow for in-camera star trail stacking. Again, a pity in a camera many will choose for astrophotography.
Nevertheless, the Average mode is a handy way to create foreground landscapes with less noise, which then have to be composited later with a sky image or images.
On the left, below, the Mark II has a nearly identical layout of buttons and controls to the 6D on the right. So owners of the older model will feel right at home with the Mark II. That’s handy, as we astrophotographers work in the dark by feel!
Of course the big new feature, a first for Canon in a full-frame camera, is the Mark II’s fully articulated screen. It flips out, tilts, and even flips around to face forward. This is super-great for all astrophotography, especially when conducted by aging photographers with aching backs!
And the screen, as with the entry-level cropped-frame Canons, is a touch screen. For someone who hasn’t used one before – me! – that’ll take some getting used to, if only in just remembering to use it.
And it remains to be seen how well it will work in the cold. But it’s great to have.
Like other late-model Canon DSLRs, the 6D MkII has a built-in intervalometer. It works fine but is useable only on exposures with internally set shutter speeds up to 30 seconds.
However, setting the Interval so it fires the shutter with a minimal gap of 1 second between shots (our usual requirement for night time-lapses) is tricky: You have to set the interval to a value not 1 second, but 2 to 3 seconds longer than the shutter speed. i.e. an exposure of 30 seconds requires an interval of 33 seconds, as shown above. Anything less and the camera misses exposures.
Why? Well, when set to 30 seconds the camera actually takes a 32-second exposure. Surprise!
Other cameras I’ve used and tested with internal intervalometers (Nikon and Pentax) behave the same way. It’s confusing, but once you are used to it, the intervalometer works fine.
Except … the manual suggests the only way to turn it off and stop a sequence is to turn off the camera. That’s crude. A reader pointed out that it is also possible to stop a time-lapse sequence by hitting the Live View Start/Stop button. However, that trick doesn’t work on sequences programmed with only a second between frames, as described above. So stopping a night time-lapse is inelegant to say the least. With Nikons you can hold down the OK button to stop a sequence, with the option then of restarting it if desired.
Also, the internal Intervalometer cannot be used for exposures longer than 30 seconds. Again, that’s the case with all in-camera intervalometers in other models and brands.
As with many other new Canons, the Mark II has a Bulb Timer function.
When on Bulb you can program in exposure times of any length. That’s a nice feature that, again, might mean an external intervalometer is not needed for many situations.
A new feature I like is the greatly expanded information when reviewing an image.
One of the several screens you can scroll to shows whether you have shot that image with Long Exposure Noise Reduction on or not.
Excellent! I have long wanted to see that information recorded in the metadata. Digital Photo Professional also displays that status, but not Adobe Camera Raw/Lightroom.
While this has been a long report, this is an important camera for us astrophotographers.
I wish the news were better, but the 6D Mark II is somewhat of a disappointment for its image quality. It isn’t bad. It’s just that it isn’t any better than than the older 6D, and in some aspects is worse.
Canon has clearly made certain compromise decisions in their sensor design. Perhaps adding in the Dual-Pixel Autofocus for rapid focusing in Movie Mode has compromised the signal-to-noise ratio. That’s something only Canon can explain.
But the bottom-line recommendations I can offer are:
If you are a Canon user looking to upgrade to your first full-frame camera, the 6D Mark II will provide a noticeable and welcome improvement in noise and performance over a cropped-frame model. But an old 6D, bought new while they last in stock, or bought used, will be much cheaper and offer slightly less noise. But the Mark II’s flip-out screen is very nice!
If you are a current 6D owner, upgrading to a Mark II will not get you better image quality, apart from the slightly better resolution. Noise is actually worse. But it does get you the flip-out screen. I do like that!
If you are not wedded to Canon, but want a full-frame camera for the benefits of its lower noise, I would recommend the Nikon D750. I have one and love it. I have coupled it with the Sigma Art series lenses. I have not used any of the Sony a7-series Mirrorless cameras, so cannot comment on their performance, but they are popular to be sure.
Learn the basics of shooting nightscape and time-lapse images with my three new video tutorials.
In these comprehensive and free tutorials I take you from “field to final,” to illustrate tips and techniques for shooting the sky at night.
At sites in southern Alberta I first explain how to shoot the images. Then back at the computer I step you through how to process non-destructively, using images I shot that night in the field.
Tutorial #1 – The Northern Lights
This 24-minute tutorial takes you from a shoot at a lakeside site in southern Alberta on a night with a fine aurora display, through to the steps to processing a still image and assembling a time-lapse movie.
Tutorial #2 – Moonlit Nightscapes
This 28-minute tutorial takes you from a shoot at Waterton Lakes National Park on a bright moonlit night, to the steps for processing nightscapes using Camera Raw and Photoshop, with smart filters, adjustment layers and masks.
Tutorial #3 – Star Trails
This 35-minute tutorial takes you from a shoot at summer solstice at Dinosaur Provincial Park, then through the steps for stacking star trail stills and assembling star trail time-lapse movies, using specialized programs such as StarStaX and the Advanced Stacker Plus actions for Photoshop.
As always, enlarge to full screen for the HD versions. These are also viewable at my Vimeo channel.
I’ve been an avowed Canon DSLR user for a decade. I may be ready to switch!
[NOTE:This review dates from 2015. Tests done today with current models would certainly differ. Canon’s EOS R mirrorless series, for example, offer much better ISO Invariancy performance but lack the “dark frame buffer” advantage of Canon DSLRs. And indeed, I have used the Nikon D750 a lot since 2015. But I did not give up my Canons!]
Here, in a technical blog, I present my tests of two leading contenders for the best DSLR camera for nightscape and astronomical photography: the Canon 6D vs. the Nikon D750. Which is better?
To answer, I subjected both to side-by-side outdoor tests, using exposures you’ll actually use in the field for typical nightscapes and for deep-sky images.
Both cameras are stock, off-the-shelf models. They have not had their filters modified for astronomy use. Both are 20- to 24-megapixel, full-frame cameras, roughly competitive in price ($1,900 to $2,300).
For images shot through lenses, I used the Canon L-Series 24mm on the Canon 6D, and the Sigma 24mm Art lens on the Nikon D750.
The bottom line:Both are great cameras, with the Nikon D750 having the edge for nightscape work, and the Canon 6D the edge for deep-sky exposures.
The 24.3-megapixel Nikon D750 has 5.9-micron pixels, while the 20.2-megapixel Canon 6D has slightly larger 6.5-micron pixels which, in theory, should lead to lower noise for the Canon. How do they compare in practice?
I shot a moonlit nightscape scene (above) at five ISO settings, from 800 to 12800, at increasingly shorter exposures to yield identically exposed frames. I processed each frame as shown above, with boosts to shadows, clarity, and contrast typical for nightscapes. However, I applied no noise reduction (either luminance or color) in processing. Nor did I take and apply dark frames.
The blowups of a small section of the frame (outlined in the box in the upper right of the Photoshop screen) show very similar levels of luminance noise. The Canon shows slightly more color noise, in particular more magenta pixels in the shadows at high ISOs. Its larger pixels didn’t provide the expected noise benefit.
TEST #2 — Resolution
Much has been written about the merits of Canon vs. Nikon re: the most rigorous of tests, resolving stars down at the pixel level.
I shot the images below of the Andromeda Galaxy the same night through a 92mm aperture apo refractor. They have had minimal but equal levels of processing applied. At this level of inspection the cameras look identical.
But what if we zoom in?
For many years Nikon DSLRs had a reputation for not being a suitable for stellar photography because of a built-in noise smoothing that affected even Raw files, eliminating tiny stars along with noise. Raw files weren’t raw. Owners worked around this by turning on Long Exposure Noise Reduction, then when LENR kicked in after an exposure, they would manually turn off the camera power.
This so-called “Mode 3” operation yielded a raw frame without the noise smoothing applied. Clearly, this clumsy workaround made it impossible to automate the acquisition of raw image sequences with Nikons.
Are Nikons still handicapped? In examining deep-sky images at the pixel-peeping level (below), I saw absolutely no difference in resolution or the ability to record tiny and faint stars. With its 4-megapixel advantage the Nikon should resolve finer details and smaller stars, but in practice I saw little difference.
On the other hand I saw no evidence for Nikon’s “star eater” reputation. I think it is time to lay this bugbear of Nikons to rest. The Nikon D750 proved to be just as sharp as the Canon 6D.
Note that in the closeups above, the red area marks a highlight (the galaxy core) that is overexposed and clipped. Nikon DSLRs also have a reputation for having sensors with a larger dynamic range than Canon, allowing better recording of highlights before clipping sets in.
However, in practice I saw very little difference in dynamic range between the two cameras. Both clipped at the same points and to the same degree.
TEST #3 — Mirror Box Shadowing
An issue little known outside of astrophotography is that a DSLR’s deeply-inset sensor can be shadowed by the upraised mirror and sides of the mirror box. Less light falls on the edges of the sensor.
The vignetting effect is noticeable only when we boost the contrast to the high degree demanded by deep-sky images, and when shooting through fast telescope systems.
Here I show the vignetting of the Canon and Nikon when shooting through my 92mm refractor at f/4.5.
The circular corner vignetting visible in the images below is from the field flattener/reducer I employed on the telescope. It can be compensated for by using Lens Correction in Adobe Camera Raw, or eliminated by taking flat fields.
The dark edge at the bottom of the frame is from shadowing by the upraised mirror. It can be eliminated only by taking flat fields, or reduced by using masked brightness adjustments in processing.
Both cameras showed similar levels of vignetting, with the Canon perhaps having the slight edge.
TEST #4 — ISO Invariancy
So far the Nikon D750 and Canon 6D are coming up fairly equal in performance. But not here. This is where the Nikon outperforms the Canon by quite a wide margin.
Sony sensors (used in Sony cameras and also used by Nikon) have a reputation for being “ISO Invariant.”
What does that mean?
In the examples above, the correct exposure for the starlit scene was 15 seconds at f/1.4 at ISO 6400. See how the two cameras rendered the scene? Very similar, albeit with the Canon showing more noise and discoloration in the dark frame corners.
What if we shoot at the same 15 seconds at f/1.4 … but at ISO 3200, 1600, 800, and 400? These are now 1-, 2-, 3-, and 4-stops underexposed, respectively.
Then we boost the Exposure setting of the underexposed Raw files later in processing, by 1, 2, 3 or 4 f-stops. What do we see?
With the Nikon (above) we see images that look nearly identical for noise to what we got with the properly exposed ISO 6400 original. It really didn’t matter what ISO speed the image was shot at – we can turn it into any ISO we want later with little penalty.
With the Canon (above) we get images with grossly worse noise in the shadows and with ugly magenta discoloration. Canons cannot be underexposed. You must use as high an ISO as needed for the correct exposure.
This “ISO Invariant” advantage of Nikon over Canon is especially noticeable in nightscapes scenes lit only by starlight, as above. The Canon turns ugly purple at -3EV underexposure, and loses all detail and contrast at -4EV underexposure.
For nightscape imaging this is an important consideration. We are limited in exposure time and aperture, and so are often working at the ragged edge of exposure. Dark areas of a scene are often underexposed and prone to noise. With the Nikon D750 these areas may still look noisy, but not much more so than they would be at that ISO speed.
With the Canon 6D, underexpose the shadows and you pay the price of increased noise and discoloration when you try to recover details in the shadows.
Apparently, the difference comes from where the manufacturer places the analog-to-digital circuitry: on the sensor (ISO invariant) or outboard on a separate circuit (ISO variant), and thus where in the signal path the amplification occurs when we boost ISO speed.
TEST #6 — Features
One could go on endlessly about features, but here I compare the two cameras on just a few key operating features very important to astrophotographers.
The Canon 6D has none, though newer Canons do. The Nikon D750, as do many Nikons, has a built-in intervalometer (shown above), even with a deflickering “Exposure Smoothing” option. However, exposure time is limited to the camera’s maximum of 30 seconds. Any longer requires an outboard intervalometer, as with the Canon.
If you use your camera with any motion control time-lapse unit, then it becomes the intervalometer, negating any capability built into the camera. But it’s nice to have.
Small Advantage: Nikon
REVISED JUNE 2020:
When taking time-lapse or star trail images with the Canon I can set an interval as short as 1 second between frames, for a minimum of gaps or jumps in the stars. With the Nikon, controlled internally by its built-in intervalometer, a 1-second interval is possible but only if you set the interval to 33 seconds for a 30-second shutter speed.
That’s true of Canon and Sony built-in intervalometers as well, because on all cameras setting the exposure to 30 seconds really gives you a 32-second exposure. A little known fact! So the interval between shutter firings has to be set to 33 seconds. It’s tricky.
Advantage: None to either
Tiltable LCD Screen:
The Canon 6D has none. The Nikon D750 has a very useful tilt-out screen as shown above. This is hugely convenient for all forms of astrophotography. Only cropped-frame Canons have tilt-out screens. This feature might add weight, but it’s worth it!
Big Advantage: Nikon
Dark Frame Buffer:
The Nikon has none. With Long Exposure Noise Reduction ON, the Canon 6D allows up to four exposures to be shot in quick succession before the dark frame kicks in and locks up the camera. (Put the camera into Raw+JPG.)
[JUNE 2020: With the Canon 6D MkII the buffer allows three frames to be taken in quick succession.]
This is very useful for deep-sky imaging, for acquiring a set of images for stacking that have each had a dark frame subtracted in-camera, with a minimum of “down-time” at the camera.
Big Advantage: Canon
Live View Screen Brightness:
As pointed out to me by colleague Christoph Malin, with the Nikon you cannot dim the screen when in Live View mode and with Exposure Simulation ON. So it can be too bright at night. With the Canon you can dim the Live View screen — the LCD Brightness control affects the screen both during Live View as well as during playback of images.
Small Advantage: Canon
Canon EOS cameras are well supported by advanced software, such as GBTimelapse (above) that controls only Canons, not Nikons, in complex time-lapse sequences, and Nebulosity, popular among deep-sky imagers for DSLR control.
Small Advantage: Canon
My take-away conclusions:
• Nikon DSLRs now are just as good for astrophotography as Canons, though that wasn’t always the case – early models did suffer from more noise and image artifacts than their Canon counterparts.
• Canon DSLRs, due to their sensor design, are more prone to exhibiting noise and image artifacts when images are greatly underexposed then boosted later in processing. Just don’t underexpose them – good advice for any camera.