How to Photograph Comet NEOWISE


Comet over Hoodoos at Dinosaur Park in Twilight (July 14, 2020)A bright comet is a once-a-decade opportunity to capture some unique nightscapes. Here are my suggested tips and FAQs for getting your souvenir shot. 

My guide to capturing Comet NEOWISE assumes you’ve done little, if any, nightscape photography up to now. Even for those who have some experience shooting landscape scenes by night, the comet does pose new challenges — for one, it moves from night to night and requires good planning to get it over a scenic landmark. 

So here are my tips and techniques, in answers to the most frequently asked questions I get and that I see on social media posts.

Comet over Hoodoos at Dinosaur Park (July 14, 2020)
Comet NEOWISE (C/2020 F3) over the eroded hoodoo formations at Dinosaur Provincial Park, Alberta, July 14-15, 2020. A faint aurora is at right. The foreground is lit by starlight only; there was no light painting employed here. This is a stack of 12 exposures for the ground to smooth noise, blended with a single untracked exposure of the sky, all at 20 seconds at f/2.8 and ISO 1600, all with the 35mm Canon lens and Canon 6D MkII camera.

How Long Will the Comet be Visible?

The comet is not going to suddenly whoosh away or disappear. It is in our northern hemisphere sky and fairly well placed for shooting and watching all summer.

But … it is now getting fainter each night so the best time to shoot it is now! Or as soon as clouds allow on your next clear night. 

As of this writing on July 18 it is still bright enough to be easily visible to the unaided eye from a dark site. How long this will be the case is unknown. 

But after July 23 and its closest approach to Earth the comet will be receding from us and that alone will cause it to dim. Later this summer it will require binoculars to see, but might still be a good photogenic target, but smaller and dimmer than it was in mid-July. 

Comet Path
This chart shows the position of Comet NEOWISE at nightly intervals through the rest of the summer. However, the rest of July are the prime nights left for catching the comet at its best. Click or tap on the image to download a full-res copy.

When is the Best Time to Shoot?

The comet has moved far enough west that it is now primarily an evening object. So look as soon as it gets dark each night. 

Until later in July it is still far enough north to be “circumpolar” for northern latitudes (above 50° N) and so visible all night and into the dawn. 

But eventually the comet will be setting into the northwest even as seen from northern latitudes and only visible in the evening sky. Indeed, by the end of July the comet will have moved far enough south that observers in the southern hemisphere anxious to see the comet will get their first looks. 

Comet NEOWISE over Red Deer River
Comet NEOWISE (C/2020 F3) over the Red Deer River from Orkney Viewpoint north of Drumheller, Alberta, on the morning of July 11, 2020. The sky is brightening with dawn twilight and a small display of noctilucent clouds is on the horizon at right. This is a two-segment vertical panorama with the 35mm Canon lens at f/2.8 and Canon 6D MkII at ISO 200 for 13 seconds each. Stitched with Adobe Camera Raw.

Where Do I Look? 

In July look northwest below the Big Dipper. By August the comet is low in the west below the bright star Arcturus. By then it will be moving much less from night to night. The chart above shows the comet at nightly intervals; you can see how its nightly motion slows as it recedes from us and from the Sun. 

Selfie Observing Comet NEOWISE (July 15, 2020)
A selfie observing Comet NEOWISE (C/2020 F3) with binoculars on the dark moonless night of July 14/15, 2020 from Dinosaur Provincial Park, Alberta. A faint aurora colours the sky green and magenta. The faint blue ion tail of the comet is visible in addition to its brighter dust tail. The ground is illuminated by starlight and aurora light only. This is a blend of 6 exposures stacked for the ground (except me) to smooth noise, and one exposure for the sky and me, all 13 seconds at f/2.5 with the 35mm lens and Canon 6D MkII at ISO 6400. Topaz DeNoise AI applied.

What Exposures Do I Use?

There is no single best setting. It depends on …

— How bright the sky is from your location (urban vs a rural site).

— Whether the Moon is up — it will be after July 23 or so when the Moon returns to the western sky as a waxing crescent.

— The phase of the Moon — in late July it will be waxing to Full on August 3 when the sky will be very bright and the comet faint enough it might lost in the bright sky.

However, here are guidelines:

— ISO 400 to 1600

— Aperture f/2 to f/4

— Shutter speed of 4 to 30 seconds

Unless you are shooting in a very bright sky, your automatic exposure settings are likely not going to work.

As with almost all nightscape photography you will need to set your camera on Manual (M) and dial in those settings for ISO, Aperture and Shutter Speed manually. Just how is something you need to consult your camera’s instruction manual for, as some point-and-shoot snapshot cameras are simply not designed to be used manually.

Panorama of Comet NEOWISE Over Prince of Wales Hotel (July 14, 2
A once-in-a-lifetime scene — A panorama of the dawn sky at 4 am on July 14, 2020 from Waterton Lakes National Park, Alberta, Canada with Comet NEOWISE (C/2020 F3) over the iconic Prince of Wales Hotel. Noctilucent clouds glow below the comet in the dawn twilight. Venus is rising right of centre paired with Aldebaran and the Hyades star cluster, while the Pleiades cluster shine above. The waning quarter Moon shines above the Vimy Peak at far right. The Big Dipper is partly visible above the mountain at far left. Capella and the stars of Auriga are at centre. This is an 8-segment panorama with the 35mm Canon lens at f/2.5 for 15 seconds each at ISO 100 with the Canon 6D MkII and stitched with Adobe Camera Raw.

Exposure Considerations 

As a rule you want to …

— Keep the ISO as low as possible for the lowest noise. The higher the ISO the worse the noise. But … do raise the ISO high enough to get a well-exposed image. Better to shoot at ISO 3200 and expose well, than at ISO 800 and end up with a dark, underexposed image.

— Shoot at a wide aperture, such as f/2 or f/2.8. The wider the aperture (smaller the f-number) the shorter the exposure can be and/or lower the ISO can be. But … lens aberrations might spoil the sharpness of the image. 

— Keep exposures short enough that the stars won’t trail too much during the exposure due to Earth’s rotation. The “500 Rule” of thumb says exposures should be no longer than 500 / Focal length of your lens. 

So for a 50mm lens exposures should be no longer than 500/50 = 10s seconds. You’ll still see some trailing but not enough to spoil the image. And going a bit longer in exposure time can make it possible to use a slower and less noisy ISO speed or simply having a better exposed shot. 

Histogram
The histogram as shown in Adobe Camera Raw. Cameras also display the image’s histogram in the Live View preview and in playback of recorded images. Keep the histogram from slamming to the left.

— Avoid underexposing. If you can, call up the “histogram”— the graph of exposure values — on the resulting image in playback on your camera. The histogram should look fairly well distributed from left to right and not all bunched up at the left. 

Comet NEOWISE Over Dinosaur Park (July 15, 2020)
This is Comet NEOWISE (C/2020 F3) over the badlands and formations of Dinosaur Provincial Park, Alberta, on the night of July 14-15, 202. This is a blend of 6 exposures for the ground stacked to smooth noise, with a single exposure for the sky, with the 35mm Canon lens and Canon 6D MkII. The ground exposures are 1- and 2-minutes at ISO 1600 and f/2.8, while the single untracked sky exposure was 20 seconds at ISO 3200 and f/2.5.

My Nightscapes and Time-Lapses ebook shown above provides extensive instruction on the best camera settings for exposure and noise reduction.

Location Considerations

When and where you are will also affect your exposure combination. 

If you are at a site with lots of lights such as overlooking a city skyline, exposures will need to be shorter than at a dark site. 

And nights with a bright Moon will require shorter exposures than moonless nights.

Take test shots and see what looks good! Inspect the histogram. This isn’t like shooting with film when we had no idea if we got the shot until it was too late! 


What Lens Do I Use?

Comet over Canola Field (July 15, 2020)
With a 35mm lens. Comet NEOWISE (C/2020 F3) over a ripening canola field near home in southern Alberta, on the night of July 15-16, 2020. This is a blend of a stack of six 2-minute exposures at ISO 3200 and f/5.6 to smooth noise, provide depth of field, and bring out the colours of the canola, blended with a single short 15-second exposure of the sky at f/2.8 and ISO 1600, all with the 35mm lens and Canon 6D MkII camera.
Comet over Canola Field Close-Up (July 15, 2020)
With a 50mm lens. Comet NEOWISE (C/2020 F3) over a ripening canola field near home in southern Alberta, on the night of July 15-16, 2020. This is a blend of a stack of three 2-minute exposures at ISO 1600 and f/5 to smooth noise, provide depth of field, and bring out the colours of the canola, blended with a single short 15-second exposure of the sky at f/2.8 and ISO 3200, all with the 50mm Sigma lens and Canon 6D MkII camera.

Any lens can produce a fine shot. Choose the lens to frame the scene well. 

Using a longer lens (105mm to 200mm) does make the comet larger, but … might make it more difficult to also frame it above a landscape. A good choice is likely a 24mm to 85mm lens.

A fast lens is best, to keep exposure times below the 500 Rule threshold and ISO speeds lower. Slow f/5.6 kit zooms can be used but do pose challenges for getting well exposed and untrailed shots. 

Shooting with shorter focal lengths can help keep the aperture wider and faster. Long focal lengths aren’t needed, especially for images of the comet over a landscape. Avoid the temptation to use that monster 400mm or 600mm telephoto wildlife lens. Unless it is on a tracker (see below) it will produce a trailed mess. It is best to shoot with no more than a 135mm telephoto, the faster the better, IF you want a close-up.

Planetarium programs that I recommend below offer “field of view” indicators so you can preview how much of the horizon and sky your camera and lens combination will show. 

StarryNightFOV
StarryNight™ and other programs offer “Field of View” indicator frames that can show how the scene will frame with (in this example) lenses from 24mm to 135mm.

Can I Use My [insert camera here] Camera?

Yes. Whatever you have, try it. 

However, the best cameras for any nightscape photography are DSLRs and Mirrorless cameras, either full-frame or cropped frame. They have the lowest noise and are easiest to set manually. 

In my experience in teaching workshops I find that the insidious menus of automatic “point-and-shoot” pocket cameras make it very difficult to find the manual settings. And some have such noisy sensors they do not allow longer exposures and/or higher ISO speeds. But try their Night or Fireworks scene modes. 

It doesn’t hurt to try, but if you don’t get the shot, don’t fuss. Just enjoy the view with your eyes and binoculars. 

But … if you have an iPhone11 or recent Android phone (I have neither!) their “Night scene” modes are superb and use clever in-camera image stacking and processing routines to yield surprisingly good images. Give them a try — keep the camera steady and shoot. 

Comet NEOWISE with NLCs Above Prairie Lake (July 10-11, 2020)
This is Comet NEOWISE (C/2020 F3) over Deadhorse Lake near Hussar in southern Alberta, taken just after midnight on July 10-11, 2020 during its evening appearance. The comet shines just above low noctilucent clouds. This is a blend of nine exposures for the ground stacked to smooth noise and the water, with a single exposure for the sky, all 4 seconds with the 135mm Canon lens at f/2 and Canon 6D MkII at ISO 1600.

What No One Asks: How Do I Focus?

Everyone fusses about “the best” exposure. 

What no one thinks of is how they will focus at night. What ruins images is often not bad exposure (a lot of exposure sins can be fixed in processing) but poor focus (which cannot be fixed later).

On bright scenes it is possible your camera’s Autofocus system will “see” enough in the scene to work and focus the lens. Great.

On dark scenes it will not. You must manually focus. Do that using your camera’s “Live View” function (all DSLRs and Mirrorless cameras have it — but check your user manual as on DSLRs it might need to be activated in the menus if you have never used it). 

Canon 6D Live View Wide
The Live View screen of a Canon DSLR. Look in your manual for tips on how to boost the Live screen image brightness with the Exposure Simulation option.
Canon 6D Live View Zoom5x
Magnify the image 5x, 10x or more with the Zoom box centred on a star to focus the star to a pinpoint.

Aim at a bright star or distant light and magnify the image 5x or 10x (with the + button) to inspect the star or light. Put the lens on MF (not AF) and focus the lens manually to make the star as pinpoint as possible. Do not touch the lens afterwards. 

Practice on a cloudy night on distant lights.

All shooting must be done with a camera on a good tripod. As such, turn OFF any image stabilization (IS), whether it be on the lens or in the camera. IS can ruin shots taken on a tripod. 


What Few Ask: How Do I Plan a Shoot? 

Good photos rarely happen by accident. They require planning. That’s part of the challenge and satisfaction of getting the once-in-a-lifetime shot. 

To get the shot of the comet over some striking scene below, you have to figure out:

— First, where the comet will be in the sky, 

— Then, where you need to be to look toward that location. 

— And of course, you need to be where the sky will be clear!

Stellarium Web
The free web version of Stellarium shows the comet, as do the paid mobile apps.
  1. Planning Where the Comet Will Be 

Popular planning software such as PhotoPills and The Photographer’s Ephemeris can help immensely, but won’t have the comet itself included in their displays, just the position of the Sun, Moon and Milky Way.

For previewing the comet’s position in the sky, I use the planetarium programs Starry Night (desktop) or SkySafari (mobile app). Both include comet positions. 

The program Stellarium (stellarium.org) is free for desktop while the mobile Stellarium Plus apps (iOS and Android) have a small fee. There is also a free web-based version at https://stellarium-web.org  Be sure to allow it to access your location. 

Set the programs to the night in question to see where the comet will be in relation to the stars and patterns such as the Big Dipper. Note the comet’s altitude in degrees and azimuth (how far along the horizon it will be). For example, an azimuth of 320° puts it in the northwest (270° is due west; 0° or 360° is due north, 315° is directly northwest). 

Comet NEOWISE and NLCs over Prince of Wales Hotel (July 14, 2020
Comet NEOWISE (C/2020 F3) with a small display of noctilucent clouds over Emerald Bay and the iconic Prince of Wales Hotel at Waterton Lakes National Park, Alberta, at dawn on July 14, 2020. This is a blend of a stack of four exposures for the ground and water to smooth noise, blended with a single short exposure for the sky, all 20 seconds at f/2.5 and ISO 400. All with the 35mm Canon lens and Canon 6D MkII camera.
  1. Planning Where You Need To Be

I use The Photographer’s Ephemeris mobile app (https://www.photoephemeris.com) — there is a free web version available. Many like PhotoPills (https://www.photopills.com).

With either you can dial in the time and date and see lines pointing toward where the Sun would be, but below the horizon. Scrub through time to move that line to the same azimuth angle as where the comet will be and then see if the comet is sitting in the right direction. 

TPE
The screen from The Photographer’s Ephemeris app showing the planning map for the image above, with the faint yellow line indicating the line toward the comet’s azimuth.

Move your location to place the line toward the comet over what you want to include in the scene.

TPE 3D
The simulation of the real scene above, of the comet over the Prince of Wales Hotel, using TPE 3D app. The simulation matches the real scene very well!

I like The Photographer’s Ephemeris as it links to the companion app TPE3D that can show the stars over the actual topographic landscape. It won’t show the comet, but if you know where it is in the sky you can see if if will clear mountains, for example.

Astrospheric
The Astrospheric app prediction of skies for me for the night I prepared this blog. Not great! But clear skies could be found to to east with a fresh hours drive.
  1. Planning for the Weather 

All is for nought if the sky is cloudy. 

For planning astro shoots I like the app Astrospheric (https://www.astrospheric.com). It is free for mobile and there is a web-based version. It uses Environment Canada predictions of cloud cover for North America. Use it to plan where to be for clear skies first, then figure out the best scenic site that will be under those clear skies. 

For sites outside North America, try ClearOutside (https://clearoutside.com) 


Advanced Techniques 

Be happy to get a well-composed and exposed single shot. 

But … if you wish to try some more advanced techniques for later processing, here are suggestions.

Comet NEOWISE and Aurora Panorama (July 13, 2020)
A panorama of the sky just before midnight on July 13, 2020 from Waterton Lakes National Park, Alberta, Canada with Comet NEOWISE (C/2020 F3) over the front range of the Rocky Mountains and an arc of aurora across the north. This is a 6-segment panorama with the 35mm Canon lens at f/2.2 for 25 seconds each at ISO 800 with the Canon 6D MkII and stitched with Adobe Camera Raw.

1. Panoramas

On several nights I’ve found a panorama captures the scene better, including the comet in context with the wide horizon, sweep of the twilight arch or, as we’ve had in western Canada, some Northern Lights.

Take several identical exposures, moving the camera 10 to 15 degrees between images. Editing programs such as Lightroom, Adobe Camera Raw, ON1 Photo RAW and Affinity Photo have panorama stitching routines built in. 

My Nightscapes and Time-Lapses ebook shown above provides tutorials for shooting and processing nightscape panoramas. 

Comet NEOWISE over Red Deer River Panorama (July 11, 2020)
What a magical scene this was! This is Comet NEOWISE (C/2020 F3) over the sweep of the Red Deer River and Badlands from Orkney Viewpoint north of Drumheller, Alberta, on the morning of July 11, 2020. Light from the waning gibbous Moon provides the illumination, plus twilight. This nicely shows the arch of the twilight colours. This is a 6-segment panorama with the 50mm Sigma lens at f/2.8 and Canon 6D MkII at ISO 400 for 13 seconds each. Stitched with Adobe Camera Raw. Topaz DeNoise AI and Sharpen AI applied.

2. Exposure Blending 

If you have a situation where the sky is bright but the ground is dark, or vice versa, and one exposure cannot record both well, then shoot two exposures, each best suited to recording the sky and ground individually. 

For example, on moonless nights I’ve been shooting 2- to 5-minute long exposures for the ground and with the lens stopped down to f/5.6 or f/8 for better depth of field to be sure the foreground was in focus. 

For a video tutorial on how to do the layering and masking in programs such as Photoshop, see my How to Shoot Moonlit Nightscapes video at https://vimeo.com/theamazingsky/moonlighttutorial. 

Comet NEOWISE over Horseshoe Canyon (July 11, 2020)
This is Comet NEOWISE (C/2020 F3) over the Horseshoe Canyon formation near Drumheller, Alberta on the night of July 10-11, 2020, taken about 2 a.m. MDT with the comet just past lower culmination with it circumpolar at this time. Warm light from the rising waning gibbous Moon provides the illumination. This is a blend of six 1- and 2-minute exposures for the ground at ISO 800 and 400 stacked to smooth noise, with a single 30-second exposure at ISO 1600 for the sky, all with the 35mm Canon lens at f/2.8 and Canon 6D MkII.

3. Exposure Stacking 

To reduce noise, it is also possible to shoot multiple exposures to stack later in processing to smooth noise. This is most useful in scenes with dark foregrounds where noise is most obvious, and where I will stack 4 to 8 images. 

Just how to do this is beyond the scope of this blog. I also give step-by-step tutorials for the process in my Nightscapes and Time-Lapses ebook shown above. It be done in Photoshop, or in specialized programs such as StarryLandscapeStacker (for MacOS) or Sequator (Windows). 

But shoot the images now, and learn later how to use them. 

Comet NEOWISE Close-Up (July 15, 2020)
A close-up of Comet NEOWISE (C/2020 F3) on the night of July 14/15, 2020 with a 135mm telephoto lens. This is a stack of nine 1-minute exposures with the 135mm Canon lens wide-open at f/2 and Canon EOS Ra camera at ISO 800. The camera was on the iOptron SkyGuider Pro tracker tracking the stars not the comet. Stacked and aligned in Photoshop.

4. Tracking the Sky 

If it is close-ups of the comet you want, then you will need to use a 135mm to 300mm telephoto lens (especially later in the summer when the comet is farther away and smaller). 

But with such lenses any exposure over a few seconds will result in lots of trailing. 

iOptron SkyGuider Pro
The iOptron SkyGuider Pro and 135mm lens used to take the close-up shot of the comet above.

The solution is a tracking device such as the Sky-Watcher Star Adventurer or iOptron SkyGuider. These need to be set up so their rotation axis aims at the North Celestial Pole near Polaris. The camera can then follow the stars for the required exposures of up to a minute or more needed to record the comet and its tails well. 

Star Adventurer Polar Axis Angle
This is the Sky-Watcher Star Adventurer. All trackers have a polar axis that needs to be aligned to the Celestial Pole, near Polaris.

Just how to use a tracker is again beyond the scope of this blog. But if you have one, it will work very well for comet shots with telephoto lenses. However, trackers are not essential for wide-angle shots, especially once the Moon begins to light the sky.

But later in the summer when the comet is fainter and smaller, a tracked and stacked set of telephoto lens images will likely be the best way to capture the comet.

Clear skies and happy comet hunting!

— Alan, July 18, 2020 /Revised July 23 / AmazingSky.com 

 

Testing the Canon 6D Mark II for Nightscapes


Canon 6DMkII vs 6D Front

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.

COMPARING NOISE

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?

6D MkII Noise at 5 ISOs 6D Mark II noise at 5 ISO speeds

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. 

6D Noise at 5 ISOs 6D noise at 5 ISO speeds

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.

6D MkII Noise at ISO 3200 6D MkII noise at ISO 3200 compared to 6D

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.

ISO INVARIANCY

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.

6D MkII ISO Variancy 6D Mark II ISO Invariancy

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.

6D ISO Variancy 6D ISO Invariancy

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. 

Underexposed shadows show less noise and discolouration in the 6D. For a comparison of the Canon 6D with the ISO Invariant Nikon D750, see my earlier Nikon vs. Canon blog from 2015. The Nikon performs much better than the 6D.

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).

ACR vs DPP-withNR ACR vs. 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.

IMAGE AVERAGING

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.

Multiple Exposure Menu 6D Mark II Multiple Exposure screen

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.

6D MkII Averaging 6D Mark II Averaging results

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.

OTHER FEATURES

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!

Canon 6DMkII vs 6D Rear 6D Mark II (left) and 6D rear views

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.

INTERVAL TIMER

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.

Interval Timer Menu 6D Mark II Interval Timer screen

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.

BULB TIMER

As with many other new Canons, the Mark II has a Bulb Timer function.

Bulb Timer Menu 6D Mark II Bulb Timer screen

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.

PLAYBACK SCREEN

A new feature I like is the greatly expanded information when reviewing an image.

Playback Menu-LENR Status 6D Mark II Playback screen

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.

CONCLUSION

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.

Eclipse Rig The 6D Mark II as part of the rig for shooting the total solar eclipse. The articulated screen will be very nice!

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.

 

You can find a thorough review of the Mark II’s performance for normal photography at DPReview at https://www.dpreview.com/reviews/canon-eos-6d-mark-ii-review

However, I hope this review aimed specifically at nightscape shooters will be of value. I have yet to test the 6D Mark II for very long-exposure tracked deep-sky images.

— Alan, August 9, 2017 / © 2017 Alan Dyer / AmazingSky.com  

 

10 Tips for Terrific Time-Lapses


eMotimo at Dino Park #1

Here are my top tips for shooting terrific still-image nightscapes … and time-lapse movies of the night sky. 

Canon 6D

1. Go for pixel size, not pixel count

When choosing a camera for night sky scenes, the most important characteristic is not number of megapixels. Just the opposite.

The best cameras are usually models with more modest megapixel counts. Each of their individual pixels is larger and so collects more photons in a given exposure time, yielding higher a signal-to-noise ratio – or lower noise, critical for night shooting.

Cameras with pixels (the “pixel pitch”) 6 to 8 microns across are best. Many high-megapixel cameras have tiny 4-micron pixels.

Large-pixel cameras are often the full-frame models, such as the Canon 5D MkIII and 6D, the Nikon D610, D750, and Df, and the Sony a7s and a7S II.

Many “cropped-frame” cameras are now 18- to 24-megapixel models with smaller, noise-prone pixels. They can certainly be used, but will require more care in exposing well at lower ISOs, and in processing to smooth out noise without blurring detail.

Manual Settings

2. Learn to fly on manual

While DSLRs and Compact System Cameras have amazing automatic functions we use none of them at night.

Instead, we use the camera on Manual or Bulb, dialling in shutter speed, aperture and ISO speed manually. We also have to focus manually, using Live View mode to focus on a bright star or distant light.

Learn the tradeoffs involved: Increasing ISO sensitivity of the sensor keeps exposure times down but increases noise. Opening up the lens aperture to f/2 or f/1.4 also keeps exposures short but introduces image-blurring aberrations, especially at the frame corners.

To prevent stars from trailing due to the sky’s motion adhere to the “500 Rule:” the maximum exposure time is roughly 500 divided by the focal length of your lens.

Histogram-Correct

3. Expose to the right 

At night, always give the sensor plenty of signal.

Use whatever combination of shutter speed, aperture and ISO will provide a well-exposed image. The image “histogram,” the graph of number of pixels at each brightness level shown above, should never be slammed to the left.

It should be a well-distributed “mountain range” of pixels, extending well to the right. If the 500 Rule restricts your shutter speed, and your desire for sharp images across the frame demands you shoot at f/2.8 or even slower, then don’t be afraid to bump up the ISO speed to whatever it takes to produce a good histogram and a well-exposed image.

Noise will look far worse if you underexpose, then try to boost the image brightness later in processing. Expose to the right!

File Format #2 7D

4. Shoot Raw!

Shoot Raw. Period.

When comparing Raw and compressed JPG versions of the same image, you can be fooled into thinking the JPGs look better (i.e. smoother) because of the noise reduction the camera has applied to the JPG that is beyond your control. However, that smoothing has also wiped out fine detail, like stars.

By shooting Raw you get to control whatever level of noise reduction and sharpening the image needs later in processing.

JPGs are also 8-bit images with a limited tonal range – or palette – in which to record the subtle gradations of brightness and colour present in our images.

Imported Raw files are 16-bit, with a much wider tonal scale and colour palette. That’s critical for all astrophotos when, even with a well-exposed image, many tonal values are down in the dark end of the range. Processing Raw images makes it possible to extract detail in the shadows and highlights.

Even when shooting a time-lapse sequence, shoot Raw.

LENR

5. Take dark frames (sometimes!)

LENR reduces noise.

It’s a topic of some debate, but in my experience it is always better to turn on the camera’s Long Exposure Noise Reduction (LENR) function when shooting individual nightscape images. Doing so forces the camera to take a “dark frame,” an exposure of equal length but with the shutter closed.

It records just the noise, which the camera then subtracts from the image. Yes, it takes twice as long to acquire an image, but the image is cleaner, with fewer noisy pixels.

This is especially true when shooting on hot summer nights (the warmer the sensor the higher the noise). That said, you cannot use LENR when shooting frames for star trail composites or time-lapse movies.

For those, the interval between images should be no more than 1 to 5 seconds. Using LENR would introduce unsightly gaps in the trails or jumps in the star motion in time-lapses.

As an alternative, it is possible to take separate dark frames at the end of the night by simply covering the lens and taking exposures of the same duration and at the same ISO as your “light frames.”

Some stacking software, such as StarStax and the Advanced Stacker Actions have places to put these dark frames, to subtract them from the stack later in processing.

811eBU4sBkL._SL1500_

6. Use fast lenses

A fast lens is your best accessory.

While the “kit zoom” lenses that come with many DSLRs are great for shooting bright twilight or Full Moon scenes, they will prove too slow for dark starlit scenes with the Milky Way.

In addition to exposing to the right and shooting Raw, the secret to great nightscapes is to shoot with fast lenses, usually “prime” lenses with fixed focal lengths. They are usually faster and have better image quality than zooms.

Your most-used lens for nightscape and time-lapse shooting is likely to be a 14mm to 24mm f/2 to f/2.8 lens.

Fortunately, because we don’t need (and indeed can’t use) autofocus we can live happily with low-cost manual lenses, such as the models made in Korea and sold under brands such as Rokinon, Samyang and Bower. They work very well.

The quarter Moon reflected in the waters of Reesor Lake, Alberta in Cypress Hills Interprovincial Park. Taken on July 5, 2014. This is with the 14mm Rokinon lens and Canon 6D at ISO800. This is a high dynamic range stack of6 exposures from 1/15 to 0.6 seconds taken just before using the camera to take a motion control time-lapse. The Moon was in conjunction with Mars (right of Moon) and Spica (left of Moon) but in the bright twilight they are not showing up here.

7. Get to know the Moon & Milky Way

For many nightscape and time-lapse shoots, the Moon is your light source for illuminating the landscape.

When the Moon is absent, the Milky Way is often your main sky subject.

Knowing where the Moon will be in the sky at its various phases, and when it will rise (in its waning phases after Full Moon) or set (in its waxing phases before Full) helps you a plan a shoot, so you’ll know whether a landscape will be well lit.

Astronomy apps for desktop computers and mobile devices are essential planning aids. A good one specifically for photographers is The Photographer’s Ephemeris.

Knowing in what season and time of night the Milky Way will be visible is essential if you want to capture it. Don’t try for Milky Way shots in spring – it isn’t up!

Me with cameras shooting time-lapses at Crawling Lake reservoir, Alberta, June 30/July 1, 2013. Perpetual twilight of summer solstice shines to the north and very weak noctilucent clouds.

8. Keep it simple to start

Don’t be seduced by the fancy gear. 

Time-lapse imaging has blossomed into a field replete with incredible gear for moving a camera incrementally during a shoot, and for automating a shoot as day turns to night.

I explain how to use all the fancy gear in my ebook, linked to below, however … Great time-lapses, and certainly still-frame nightscapes, can be taken with no more than a DSLR camera with a good fast lens and mounted on a sturdy tripod. Invest in the lens and don’t scrimp on the tripod.

Another essential for shooting multi-frame star trails and time-lapses is a hardware intervalometer ($50 to $150).

TC-80N3 Masked

9. Learn the intricacies of intervals

For time-lapses, an intervalometer is essential.

Mastering exposure and focus in still images is essential for great time-lapse movies because they are simply made of hundreds of well-exposed still frames.

But move to time-lapses and you have additional factors to consider: how many frames to shoot and how often to shoot them. A good rule of thumb is to shoot 200 to 300 frames per sequence, shot with an interval of no more than 1 to 5 seconds between exposures, at least for starry night sequences.

However, most intervalometers (the Canon TC-80N3 is an exception) define their “Interval” setting to mean the time from when the shutter opens to when it opens again. In that case, you set the Interval to be a value 1 to 5 seconds longer than the exposure time you are using. That’s also true of the intervalometer function Nikon builds into their internal camera firmware.

Test first!

The summer Milky Way with a meteor streaking at centre as a bonus. An aurora to the north off frame is lighting the foreground with a green glow. Haze and forest fire smoke obscure the horizon. I shot this at the Battle Scene viewpoint at Writing-on-Stone Provincial Park, in southern Alberta. Sagittarius and the galactic centre is on the horizon at left of centre. Capricornus is amid the haze at left of centre. On the horizon are the Sweetgrass Hills in Montana. The Milk River winds below amid the sandstone formations that are home to historic First Nations petroglyphs.  This is a single 30-second exposure with the Nikon D750 at ISO 3200 and Sigma 24mm Art lens at f/2, taken as part of a time-lapse sequence.

10. Go to beautiful places

While the gear can be simple, great shots demand an investment in time.

By all means practice at home and at nearby sites that are quick to get to. Try out gear and techniques at Full Moon when exposures are short (the Full Moon is bright!) and you can see what you are doing.

But beautiful images of landscapes lit by moonlight or starlight require you to travel to beautiful locations.

When you are on site, take the time to frame the scene well, just as you would during the day. Darkness is no excuse for poor composition!

While shooting nightscapes and time-lapses can be done with a minimal investment in hardware and software, it does require an investment in time – time to travel and spend nights shooting at wonderful places under the stars.

Enjoy the night!

I cover all these topics, and much more, in detail in my ebook How to Photograph & Process Nightscapes and Time-Lapses. Click the link below to learn more.

— Alan, September 16, 2015 / © 2015 Alan Dyer / www.AmazingSky.com

Canon vs. Nikon for Astrophotography


Canon and Nikon Cameras

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.

NOTE: Click on the test images for higher-resolution versions for closer inspection. All images and text © 2015 Alan Dyer and may not be reproduced without my permission.


TEST #1 — Noise

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?

The scene used to test for noise (here with the Nikon images) showing the development settings applied to both the Nikon and Canon sets. NO noise reduction (colour or lunminance) was applied to any of the images, but Exposure, Shadows, Contrast and Clarity were boosted, and Highlights reduced.
The scene used to test for noise (here with the Nikon images) showing the development settings applied to both the Nikon and Canon sets. NO noise reduction (colour or lunminance) was applied to any of the images, but Exposure, Shadows, Contrast and Clarity were boosted, and Highlights reduced.

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.

Noise - Canon

Noise - Nikon

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.

M31 (Canon 6D)

M31 (Nikon D750)

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.

Closeup of telescope view of Andromeda Galaxy with Canon 6D 4 minute exposure at ISO 800 No noise reduction applied in processing
Closeup of telescope view of Andromeda Galaxy with Canon 6D
4 minute exposure at ISO 800
No noise reduction applied in processing
Closeup of telescope view of Andromeda Galaxy with Nikon D750 4 minute exposure at ISO 800 No noise reduction applied in processing
Closeup of telescope view of Andromeda Galaxy with Nikon D750
4 minute exposure at ISO 800
No noise reduction applied in processing

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.

Demonstrating the level of vignetting and mirror-box shadowing with the Canon 6D on a TMB 92mm apo refractor with a 0,85x field flattener/reducer lens
Demonstrating the level of vignetting and mirror-box shadowing with the Canon 6D on a TMB 92mm apo refractor with a 0.85x field flattener/reducer lens
Demonstrating the level of vignetting and mirror-box shadowing with the Nikon D750 on a TMB 92mm apo refractor with a 0,85x field flattener/reducer lens
Demonstrating the level of vignetting and mirror-box shadowing with the Nikon D750 on a TMB 92mm apo refractor with a 0.85x field flattener/reducer lens

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?

A typical Milky Way nightscape with the Nikon D750 and Sigma 24mm Art lens. With no Moon, shot at very high ISO of 6400 and wide aperture of f/1.4 to show image quality under these demanding shooting circumstances. Lens correction and basic development setttings applied.
A typical Milky Way nightscape with the Nikon D750 and Sigma 24mm Art lens.
With no Moon, shot at very high ISO of 6400 and wide aperture of f/1.4 to show image quality under these demanding shooting circumstances.
Lens correction and basic development setttings applied.
A typical Milky Way nightscape with the Canon 6D and Canon 24mm L lens (original model). With no Moon, shot at very high ISO of 6400 and wide aperture of f/1.4 to show image quality under these demanding shooting circumstances. Lens correction and basic development setttings applied.
A typical Milky Way nightscape with the Canon 6D and Canon 24mm L lens (original model).
With no Moon, shot at very high ISO of 6400 and wide aperture of f/1.4 to show image quality under these demanding shooting circumstances.
Lens correction and basic development setttings applied.

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?

Nikon D750 - Comparing ISO Invariancy from ISO 6400 to 400 (Nightscape)
Nikon D750 – Comparing ISO Invariancy from ISO 6400 to 400 (Nightscape)

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.

Canon 6D - Comparing ISO Invariancy from ISO 6400 to 400 (Nightscape)
Canon 6D – Comparing ISO Invariancy from ISO 6400 to 400 (Nightscape)

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.

 For more technical information on the topic of ISO invariancy, see DPReview.com and many of their recent reviews of DSLRs, such as this page about the Canon 5Ds/r models. 

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.

Nikon Intervalometer Start

Intervalometer:

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


Interval Length:

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


Nikon D750 with Radian

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 with GBTimelapse

Software Compatibility:

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.


All images and text are © 2015 Alan Dyer.

– Alan, August 27, 2015 & Revised June 25, 2020 / © 2015 Alan Dyer / www.amazingsky.com