Conjunctions, Satellites & Auroras, Oh My!


Friday the 13th Aurora Title

October has brought clear skies and some fine celestial sights. Here’s a potpourri of what was up from home. 

We’ve enjoyed some lovely early autumn weather here in southern Alberta, providing great opportunities to see and shoot a series of astronomical events.


Conjunctions

Venus & Mars in Close Conjunction #2 (Oct 5, 2017)
Venus and Mars in close conjunction in the dawn sky on October 5, 2017. Venus is the brightest object; Mars is below it; while the star above Venus is 4th magnitude Sigma Leonis. The foreground is illuminated by light from the setting Full Moon in the west. This is a single 1-second exposure with the 135mm lens at f/2 and Canon 60Da at ISO 800. 

On October 5, Venus and Mars appeared a fraction of a degree apart in the dawn twilight. Venus is the brightest object, just above dimmer but red Mars. This was one of the closest planet conjunctions of 2017. Mars will appear much brighter in July and August 2018 when it makes its closest approach to Earth since 2003.


Satellites: The Space Station

Overhead Pass of the Space Station in Moonlight
An overhead pass of the ISS on October 5, 2017, with the Full Moon rising in the east at left. The ISS is moving from west (at right) to east (at left), passing nearly overhead at the zenith at centre. North is at the top, south at bottom in this fish-eye lens image with an 8mm Sigma fish-eye lens on the Canon 6D MkII camera. This is a stack of 56 exposures, each 4 seconds long at an interval of 1 second. 

The Space Station made a series of ideal evening passes in early October, flying right overhead from my site at latitude 51° N. I captured it in a series of stacked still images, so it appears as a dashed line across the sky. In reality it looks like a very bright star, outshining any other natural star. Here, it appears to fly toward the rising Moon.


Satellites: Iridiums

Twin Iridium Satellite Flares (October 9, 2017)
A pair of nearly simultaneous and parallel Iridium satellite flares, on October 9, 2017, as they descended into the north. The left or westerly flare was much brighter and with a sharp rise and fall in brightness. While it was predicted to be mag. -4.4 I think it got much brighter, perhaps mag -7, but very briefly. These are Iridium 90 (left) and Iridium 50 (right). This is a stack of 40+ exposures each, 2 seconds at 1-second intervals, with the Sigma 24mm lens at f/1.4 and Nikon D750 at ISO 6400.

Often appearing brighter than even the ISS, Iridium satellite flares can blaze brighter than even Venus at its best. One did so here, above, in another time-lapse of a pair of Iridium satellites that traveled in parallel and flared at almost the same time. But the orientation of the reflective antennas that create these flares must have been better on the left Iridium as it really shot up in brilliance for a few seconds.


Auroras

Aurora and Circumpolar Star Trails (Oct, 13, 2017)
A circumpolar star trail composite with Northern Lights, on October 13, 2017, shot from home in southern Alberta. The Big Dipper is at bottom centre; Polaris is at top centre at the axis of the rotation. The bottom edge of the curtains are rimmed with a pink fringe from nitrogen. This is a stack of 200 frames taken mostly when the aurora was a quiescent arc across the north before the substorm hit. An additional single exposure is layered in taken about 1 minute after the main star trail set to add the final end point stars after a gap in the trails. Stacking was with the Advanced Stacker Plus actions using the Ultrastreaks mode to add the direction of motion from the tapering trails. Each frame is 3 seconds at f/2 and ISO 6400 wth the Sigma 14mm lens and Nikon D750.

Little in the sky beats a fine aurora display and we’ve had several of late, despite the Sun being spotless and nearing a low ebb in its activity. The above shot is a composite stack of 200 images, showing the stars circling the celestial pole above the main auroral arc, and taken on Friday the 13th.

Aurora from October 13, 2013
A decent aurora across the north from home in southern Alberta, on Friday the 13th, October, 2017, though these frames were taken after midnight MDT. 3 seconds at f/2 and ISO 6400 wth the Sigma 14mm lens and Nikon D750.

This frame, from some 1300 I shot this night, October 13, captures the main auroral arc and a diffuse patch of green above that pulsed on and off.

You can see the time-lapse here in my short music video on Vimeo.

Friday the 13th Aurora from Alan Dyer on Vimeo.

It’s in 4K if your monitor and computer are capable. It nicely shows the development of the aurora this night, from a quiescent arc, through a brief sub-storm outburst, then into pulsing and flickering patches. Enjoy!


What all these scenes have in common is that they were all shot from home, in my backyard. It is wonderful to live in a rural area and to be able to step outside and see these sites easily by just looking up!

— Alan, October 16, 2017 / © 2017 Alan Dyer / AmazingSky.com 

 

My 2018 Amazing Sky Calendar


2018 Sky Calendar CoverMy free Amazing Sky Calendar for 2018 is now available for download! Plan your astronomical year!

As in recent years, I have prepared a free 12-month Calendar listing loads of celestial events, Moon phases, highlighted space events, and with small charts to show what’s happening in the sky for the coming year. The monthly pages are illustrated with my favourite images from 2017.

You can download it as a 25-megabyte PDF at my website at

http://www.amazingsky.com/aboutalan.html

Scroll down the page for the button link.

You can print the Calendar as you wish for your personal use.

Do tell others about the Calendar, but please send them to my page for them to download the PDF Calendar for themselves.

Thanks, and here’s to a great celestial 2018!

— Alan, October 8, 2017 / © 2017 Alan Dyer / amazingsky.com

The Aurora Starring Steve


"Steve," the Strange Auroral Arc (Spherical Fish-Eye Projection)

I’ve assembled a music video of time-lapse clips and still images of the fine aurora of September 27, with Steve making a cameo appearance.

The indicators this night didn’t point to a particularly great display, but the sky really performed.

The Northern Lights started low across the north, in a very active classic arc. The display then quietened.

But as it did so, and as is his wont, the isolated arc that has become known as Steve appeared across the south in a sweeping arc. The Steve arc always defines the most southerly extent of the aurora.

Steve faded, but then the main display kicked up again and began to fill the sky with a post-sub-storm display of pulsing rays and curtains shooting up to the zenith. Only real-time video can really capture the scene as the eye sees it, but the fast time-lapses I shot do a decent job of recording the effect of whole patches of sky turning on and off.

The display ended with odd pulsing arcs in the south.

Here’s the video, available in 4K resolution.

Alberta Aurora (Sept. 27, 2017) from Alan Dyer on Vimeo.

Expand to fill the screen for the best view.

Thanks for looking!

— Alan, October 7, 2017 / © 2017 Alan Dyer / AmazingSky.com 

 

The Fast 14s Face-Off


Sigma and Rokinon 14mm on Stars

I put two new fast 14mm lenses to the test: the Sigma 14mm f/1.8 Art vs. the Rokinon 14mm f/2.4 SP. 

Much to the delight of nightscape and astrophotographers everywhere we have a great selection of new and fast wide-angle lenses to pick from.

Introduced in 2017 are two fast ultra-wide 14mm lenses, from Sigma and from Rokinon/Samyang. Both are rectilinear, not fish-eye, lenses.

I tested the Nikon version of the Sigma 14mm f/1.8 Art lens vs. the Canon version of the Rokinon 14mm f/2.4 SP. I used a Nikon D750 and Canon 6D MkII camera.

I also tested the new faster Rokinon SP against the older and still available Rokinon 14mm f/2.8, long a popular lens among nightscape photographers.

The Sigma 14mm is a fully automatic lens with auto focus. It is the latest in their highly regarded Art series of premium lenses. I have their 20mm and 24mm Art lenses and love them.

The Rokinon 14mm SP (also sold under the Samyang brand) is a manual focus lens, but with an AE chip so that it communicates with the camera. Adjusting the aperture is done on the camera, not by turning a manual aperture ring, as is the case with many of Rokinon’s lower cost series of manual lenses. The lens aperture is then recorded in each image’s EXIF metadata, an aid to later processing. It is part of Rokinon’s premium “Special Performance” SP series which includes an 85mm f/1.2 lens.

All units I tested were items purchased from stock, and were not supplied by manufacturers as samples for testing. I own these!


CONCLUSIONS

For those with no time to read the full review, here are the key points:

• The Sigma f/1.8 Art exhibits slightly more off-axis aberrations than the Rokinon 14mm SP, even at the same aperture. But aberrations are very well controlled.

• As its key selling point, the Sigma offers another full stop of aperture over the Rokinon SP (f/1.8 vs. f/2.4), making many types of images much more feasible, such as high-cadence aurora time-lapses and fixed-camera stills and time-lapses of a deeper, richer Milky Way.

• The Sigma also has lower levels of vignetting (darkening of the frame corners) than the Rokinon 14mm SP, even at the same apertures.

• Both the Sigma Art and Rokinon SP lenses showed very sharp star images at the centre of the frame.

• Comparing the new premium Rokinon 14mm SP against the older Rokinon 14mm f/2.8 revealed that the new SP model has reduced off-axis aberrations and lower levels of vignetting than the lower-cost f/2.8 model. However, so it should for double the price or more of the original f/2.8 lens.

• The Rokinon 14mm SP is a great choice for deep-sky imaging where optical quality is paramount. The Sigma 14mm Art’s extra speed will be superb for time-lapse imaging where the f/1.8 aperture provides more freedom to use shorter shutter speeds or lower ISO settings.

Though exhibiting the lowest image quality of the three lenses, the original Rokinon 14mm f/2.8 remains a superb value, at its typical price of $350 to $500. For nightscapers on a budget, it’s an excellent choice.

 


TESTING PROCEDURES

For all these tests I placed the camera and lens on a tracking mount, the Sky-Watcher Star Adventurer Mini shown below. This allowed the camera to follow the sky, preventing any star trailing. Any distortions you see are due to the lens, not sky motion.

Sigma on SAM on Stars
Star Adventurer Mini Tracker (with Sigma 14mm on Nikon D750)

As I stopped down the aperture, I lengthened the exposure time to compensate, so all images were equally well exposed.

In developing the Raw files in Adobe Camera Raw, I applied a standard level of Contrast (25) and Clarity (50) boost, and a modest colour correction to neutralize the background sky colour. I also applied a standard level of noise reduction and sharpening.

However, I did not apply any lens corrections that, if applied, would reduce lateral chromatic aberrations and compensate for lens vignetting.

So what you see here is what the lens produced out of the camera, with no corrections. Keep in mind that the vignetting you see can be largely compensated for in Raw development, with the provisos noted below. But I wanted to show how much vignetting each lens exhibited.


OFF-AXIS ABERRATIONS

Stars are the severest test of any lens. Not test charts, not day shots of city skylines. Stars.

The first concern with any fast lens is how sharp the stars are not only in the centre of the frame, but also across the frame to the corners. Every lens design requires manufacturers to make compromises on what lens aberrations they are going to suppress at the expense of other lens characteristics. You can never have it all!

However, for astrophotography we do look for stars to be as pinpoint as possible to the corners, with little coma and astigmatism splaying stars into seagull and comet shapes. Stars should also not become rainbow-coloured blobs from lateral chromatic aberration.

SIGMA 14mm ART

Sigma 14mm Upper L Corner
Sigma 14mm Art – Upper Left Corner Close-up at 5 Apertures
Sigma 14mm Upper R Corner
Sigma 14mm Art – Upper Right Corner Close-up at 5 Apertures

These images show 200% blowups of the two upper corners of the Sigma 14mm Art lens, each at five apertures, from wide open at f/1.8, then stopped down at 1/3rd stop increments to f/2.8. As you would expect, performance improves as you stop down the lens, though some astigmatism and coma are still present at f/2.8.

But even wide open at f/1.8, off-axis aberrations are very well controlled and minimal. You have to zoom up this much to see them.

There was no detectable lateral chromatic aberration.

Aberrations were also equal at each corner, showing good lens centering and tight assembly tolerances.

ROKINON 14mm SP

14mm Rokinons Aberrations (Upper L Corner)
Rokinon 14mm SP – Upper Left Corner Close-up at 3 Apertures
14mm Rokinons Aberrations (Upper R Corner)
Rokinon 14mm SP – Upper Right Corner Close-up at 3 Apertures

Similarly, these images show 200% blow-ups of the upper corners of the Rokinon SP, at its three widest apertures: f/2.4, f/2.8 and f/3.2.

Star images look tighter and less aberrated in the Rokinon, even when compared at the same apertures.

But images look better on the left side of the frame than on the right, indicating a slight lens de-centering or variation in lens position or figuring, a flaw noted by other users in testing Rokinon lenses. The difference is not great and takes pixel-peeping to see. Nevertheless, it is there, and may vary from unit to unit. This should not be the case with any “premium” lens.

SIGMA vs. ROKINON

Rokinon vs Sigma (Corner Aberrations)
Rokinon vs. Sigma Corner Aberrations Compared

This image shows both lenses in one frame, at the same apertures, for a more direct comparison. The Rokinon SP is better, but of course, doesn’t go to f/1.8 as does the Sigma.


ON-AXIS ABERRATIONS

We don’t want good performance at the corners if it means sacrificing sharp images at the centre of the frame, where other aberrations such as spherical aberration can take their toll and blur images.

These images compare the two lenses in 200% blow-ups of an area in the Cygnus Milky Way that includes the Coathanger star cluster. Both lenses look equally as sharp.

SIGMA 14mm ART

Sigma 14mm Centre
Sigma 14mm Art – Centre of Frame Close-up

Even when wide open at f/1.8 the Sigma Art shows very sharp star images, with little improvement when stopped down. Excellent!

ROKINON 14mm SP

Rokinon 14mm Centre
Rokinon 14mm SP – Centre of Frame Close-up

The same can be said for the Rokinon SP. It performs very well when wide open at f/2.4, with star images as sharp as when stopped down 2/3rds of an f-stop to f/3.2

SIGMA vs. ROKINON

Rokinon vs Sigma (Centre Aberrations)
Sigma vs. Rokinon Centre Sharpness Compared

This image shows both lenses in one frame, but with the Sigma wide open at f/1.8 and stopped down to f/2.8, vs. the Rokinon wide open at f/2.4 and stopped to f/2.8. All look superb.


VIGNETTING

The bane of wide-angle lenses is the light fall-off that is inevitable as lens focal lengths decrease. We’d like this vignetting to be minimal. While it can be corrected for later when developing the Raw files, doing so can raise the visibility of noise and discolouration, such as magenta casts. The less vignetting we have to deal with the better.

As with off-axis aberrations, vignetting decreases as lenses are stopped down. Images become more uniformly illuminated across the frame, with less of a “hot spot” in the centre.

SIGMA 14mm ART

Sigma 14mm Vignetting (5 Apertures)
Sigma 14mm Art – Vignetting Compared at 5 Apertures

This set compares the left edge of the frame in the Sigma SP at five apertures, from f/1.8 to f/2.8. You can see how the image gets brighter and more uniform as the lens is stopped down. (The inset image at upper right show what part of the frame I am zooming into.)

ROKINON 14mm SP

Rokinon 14mm Vignetting (3 Apertures)
Rokinon 14mm SP – Vignetting Compared at 3 Apertures

This similar set compares the frame’s left edge in the Rokinon SP at its three widest apertures, from f/2.4 to f/3.2. Again, vignetting improves but is still present at f/3.2.

SIGMA vs. ROKINON

Rokinon vs Sigma Vignetting
Rokinon vs. Sigma – Vignetting Compared

This compares both lenses at similar apertures side by side for a direct comparison. The Sigma is better than the Rokinon with a much more uniform illumination across the frame.

Sigma 14mm Vignetting at f1.8
Sigma 14mm Art – Vignetting at f/1.8 Maximum Aperture
Rokinon 14mm Vignetting at f2.4
Rokinon 14mm SP – Vignetting at f/2.4 Maximum Aperture

In these two images, above, of the entire frame at their respectively widest apertures, I’d say the Sigma exhibits less vignetting than the Rokinon, even when wide open at f/1.8. The cost for this performance, other than in dollars, is that the Sigma is a large, heavy lens with a massive front lens element.


ROKINON 14mm f/2.4 SP vs. ROKINON 14mm f/2.8 Standard

Even the Rokinon 14mm SP, though a manual lens, carries a premium price, at $800 to $1000 U.S., depending on the lens mount.

Samyang 14mm Lens
The 14mm Rokinon/Samyang f/2.8 Lens

For those looking for a low-cost, ultra-wide lens, the original Rokinon/Samyang 14mm f/2.8 (shown above) is still available and popular. It is a fully manual lens, though versions are available with a AE chip to communicate lens aperture information to the camera.

I happily used this f/2.8 lens for several years. Before I sold it earlier in 2017 (before I acquired the Sigma 14mm), I tested it against Rokinon’s premium SP version.

The older f/2.8 lens exhibited worse off-axis and on-axis aberrations and vignetting than the SP, even with the SP lens set to the same f/2.8 aperture. But image quality of the original lens is still very good, and the price is attractive, at half the price or less, than the 14mm SP Rokinon.

TWO 14mm ROKINONS: OFF-AXIS ABERRATIONS

14mm Rokinons Aberrations (Upper L Corner)
Two Rokinons (Older “Standard” vs. new SP) – Upper Left Corner Close-up
14mm Rokinons Aberrations (Upper R Corner)
Two Rokinons (Older “Standard” vs. new SP) – Upper Right Corner Close-up

Here, in closeups of the upper corners, I show the difference between the two Rokinons, the older standard lens on the left, and the new SP on the right.

The SP, as it should, shows lower aberrations and tighter star images, though with the improvement most marked on the left corner; not so much on the right corner. The original f/2.8 lens holds its own quite well.

TWO 14mm ROKINONS: ON-AXIS ABERRATIONS

14mm Rokinons Aberrations (Centre)
Two Rokinons (Older “Standard” vs. new SP) – Centre of Frame Close-up

At the centre of the frame, the difference is more apparent, with the SP lens exhibiting sharper star images than the old 14mm with its generally softer, larger star images. The latter likely has more spherical aberration.

TWO 14mm ROKINONS: VIGNETTING

14mm Rokinons Vignetting
Two Rokinons (Older “Standard” vs. new SP) – Vignetting Compared

The new SP lens clearly has the advantage here, with less vignetting and brighter corners even when wide open at f/2.4 than the older lens does at its widest aperture of f/2.8. This is another reason to go for the new SP if image quality is paramount


PRICES

The new Sigma 14mm Art lens is costly, at $1600 U.S., though with a price commensurate with its focal length and aperture. Other premium lenses in this focal length range, either prime or zoom, from Nikon and Canon sell for much more, and have only an f/2.8 maximum aperture. So in that sense, the Sigma Art is a bargain.

The new Rokinon 14mm SP sells for $800 to $1000, still a premium price for a manual focus lens. But its optical quality competes with the best.

The older Rokinon 14mm f/2.8 is a fantastic value at $350 to $500, depending on lens mount and AE chip. For anyone getting into nightscape and Milky Way photography, it is a great choice.


RECOMMENDATIONS

With such a huge range in price, what should you buy?

A 14mm is a superb lens for nightscape shooting – for sky-filling auroras, for panoramas along the Milky Way, or of the entire sky. But the lens needs to be fast. All three lenses on offer here satisfy that requirement.

Sigma 14mm & Rokinon 14mm SP (Front)
Sigma 14mm Art (left) and Rokinon 14mm SP (right)

SIGMA 14mm f/1.8 ART

If you want sheer speed, this is the lens. It offers a full stop gain over the already fast Rokinon f/2.5, allowing exposures to be half the length, or shooting at half the ISO speed for less noise.

Its fast speed comes into its own for rapid cadence aurora time-lapses, to freeze auroral motion as much as possible in exposures as short as 1 to 2 seconds at a high ISO. The fast speed might also make real-time movies of the aurora possible on cameras sensitive and noiseless enough to allow video shooting at ISO 25,000 and higher, such as the Sony a7s models.

The Sigma’s fast speed also allows grabbing rich images of the Milky Way in exposures short enough to avoid star trailing, either in still images or in time-lapses of the Milky Way in motion.

While the Sigma does exhibit some edge aberrations, they are very well controlled (much less than I see with some 24mm and 35mm lenses I have) and are a reasonable tradeoff for the speed and low level of vignetting, which results in less noisy corners.

Photographers obsess over corner aberrations when, for fixed-camera nightscape shooting, a low level of vignetting is probably more critical. Correcting excessive vignetting introduces noise, while the corner aberrations may well be masked by star trailing. Only in tracked images do corner aberrations become more visible, as in the test images here.

I’d suggest the Sigma is the best choice for nightscape and time-lapse shooting, with its speed allowing for kinds of shots not possible otherwise.

The Sigma also appears to be the best coated of all the lenses, as you can see in the reflections in the lenses in the opening image, and below. However, I did not test the lenses for flares and ghosting.

As a footnote, none of the lenses allow front-mounted filters, and none have filter drawers.

ROKINON 14mm f/2.4 SP

For less money you get excellent optical quality, though with perhaps some worrisome variation in how well the lens elements are figured or assembled, as evidenced by the inconsistent level of aberration from corner to corner.

Nevertheless, stars are tight on- and off-axis, and vignetting is quite low, for corners that will be less noisy when the shadows are recovered in processing.

I’d suggest the Rokinon SP is a great choice if tracked deep-sky images are your prime interest, where off-axis performance is most visible. However, the SP’s inconsistent aberrations from corner to corner are evidence of lower manufacturing tolerances than Sigma’s, so your unit may not perform like mine.

For nightscape work, the SP’s f/2.4 aperture might seem a minor gain over Rokinon’s lower-cost f/2.8 lens. But it is 1/3 of an f-stop. That means, for example, untracked Milky Way exposures could be 30 seconds instead of 40 seconds, short enough to avoid obvious star trailing. At night, every fraction of an f-stop gain is welcome and significant.

ROKINON 14mm f/2.8 Standard

You might never see the difference in quality between this lens and its premium SP brother in images intended for time-lapse movies, even at 4K resolution.

But those intending to do long-exposure deep-sky imaging, as these test images are, will want the sharpest stars possible across the frame. In which case, consider the 14mm SP.

But if price is a prime consideration, the original f/2.8 Rokinon is a fine choice. You’ll need to apply a fair amount of lens correction in processing, but the lens exists in the Camera Raw/Lightroom database, so correction is just a click away.


Sigma and Rokinon 14mm on Stars

That was a lengthy report, I know! But there’s no point in providing recommendations without the evidence to back them up.

All images, other than the opening “beauty shot,” can be clicked/tapped on to download a full-resolution original JPG for closer inspection.

As I’ve just received the Sigma Art lens I’ve not had a chance to shoot any “real” nightscape images with it yet, just these test shots. But for a real life deep-sky image of the Milky Way shot with the Rokinon SP, see this image from Australia. https://flic.kr/p/SSQm7G

I hope you found the test of value in helping you choose a lens.

Clear skies!

— Alan, September 22, 2017 / © 2017 Alan Dyer / amazingsky.com

 

Dawn Sky Delights


Aldebaran About to be Occulted by the Moon

It was one of those mornings when the sky was full of wonder.

After days and nights of smoke from unfortunate fires burning not far away, including in my favourite national park of Waterton Lakes, the sky cleared enough this morning, September 12, to reveal some fine sights.

At 6 a.m. the waning gibbous Moon passed in front of the star Aldebaran in Taurus. It is performing many such occultations of Aldebaran this year, but most aren’t well seen from any one location. This one was ideal, right from my backyard.

The lead image is a “high dynamic range” stack of several exposures showing the waning Moon and star set in some high haze adding the sky colours.

The star winked out behind the Moon’s bright limb as the Moon advanced from right to left (west to east) against the background sky.

Occultation of Aldebaran
Aldebaran nearing the limb of the Moon.
This shows a composite sequence, with images of the star taken every four minutes blended with a single image of the Moon. While it looks like the star is moving, it is really the Moon that is edging closer to Aldebaran.

The star reappeared from behind the dark limb of the Moon, but five minutes after sunrise, with the Moon in a bright blue sky. Still, the star stood out nicely in binoculars and in the telescope for this view.

Aldebaran Near the Moon in Day Sky
Aldebaran off the dark limb of the Moon.
Aldebaran is the point of light at right, just off the invisible edge of the Moon.

I shot stills and video, and compiled them into this short video.

Enlarge it to full screen to view it properly.

Meanwhile, over to the east the twilight sky was awash in planets.

Rocky Planets at Dawn with Labels (Sept. 12, 2017)
The line of dawn planets, with labels.
All the three inner terrestrial worlds were there: Venus, at top, Mercury below Regulus, and Mars lowest of the trio. Of course, a fourth terrestrial world is in the photo, too – Earth!

Mercury was at its greatest western elongation this morning, placing it as far from the Sun and as high in the sky as it gets, with this autumn appearance the best of 2017 for a morning showing for Mercury. Even so, you can see how Mercury is always low and easy to miss. However, this morning it was obvious to the naked eye.

Mars and Mercury will be in close conjunction at dawn on the morning of September 16.

Rocky Planets at Dawn (Sept. 12, 2017)

It was a fine morning to be up early and enjoy the solar system show.

— Alan, September 12, 2017 / © 2017 Alan Dyer / amazingsky.com

 

Testing the Canon 6D Mark II for Deep-Sky


6D MkII on Cygnus

Following up on my earlier tests, I compare the new Canon 6D MkII camera to earlier Canon full-frame models in long, tracked exposures of the Milky Way.

A month ago I published tests of the new Canon 6D MkII camera for nightscape images, ones taken using a fixed tripod in which exposures usually have to be limited to no longer than 30 to 60 seconds, to prevent star trailing.

Despite these short exposures, we still like to extract details from the dark shadows of the scene, making nightscape images a severe test of any camera.

I refer you to my August 9, 2017 blog Testing the Canon 6D MkII for Nightscapes for the results. The 6D MkII did not fare well.

Here I test the 6D MkII for what, in many respects, is a less demanding task: shooting long exposures of deep-sky objects, the Milky Way in Cygnus in this case.

Why is this an easier task? The camera is now on a tracking mount (I used the new Sky-Watcher Star Adventurer Mini) which is polar aligned to follow the rotation of the sky. As such, exposures can now be many minutes long if needed. We can give the camera sensor as much signal as the darkness of the night sky allows. More signal equals less noise in the final images.

In addition, there are no contrasty, dark shadows where noise lurks. Indeed, the subjects of deep-sky images are often so low in contrast, as here, they require aggressive contrast boosting later in processing to make a dramatic image.

While that post-processing can bring out artifacts and camera flaws, as a rule I never see the great increase in noise, banding, and magenta casts I sometimes encounter when processing short-exposure nightscape scenes.


6D MkII at Four ISOs
The Canon 6D MkII at four typical ISO speeds in tracked exposures.

6D at Four ISOs
The original Canon 6D at four typical ISO speeds in tracked exposures.

5D MkII at Four ISOs
A Canon 5D MkII that has been filter-modified at four typical ISO speeds in tracked exposures.
For this test, I shot the same region of sky with the same 35mm lens L-Series lens at f/2.2, using three cameras:

• Canon 6D MkII (2017)

• Canon 6D (2012)

• Canon 5D MkII (2008)

Note that the 5D MkII has been “filter-modified” to make its sensor more sensitive to the deep red wavelengths emitted by hydrogen gas, the main component of the nebulas along the Milky Way. You’ll see how it picks up the red North America Nebula much better than do the two off-the-shelf “stock” cameras. (Canon had their own factory-modified “a” models in years past: the 20Da and 60Da. Canon: How about a 6D MkIIa?)

I shot at four ISO speeds typical of deep-sky images: 800, 1600, 3200, and 6400.

Exposures were 4 minutes, 2 minutes, 1 minute, and 30 seconds, respectively, to produce equally exposed frames with a histogram shifted well to the right, as it should be for a good signal-to-noise ratio.

Noisy deep-sky images with DSLR cameras are usually the result of the photographer underexposing needlessly, often in the mistaken belief that doing so will reduce noise when, in fact, it does just the opposite.

The above set of three images compares each of the three cameras at those four ISO speeds. In all cases I have applied very little processing to the images: only a lens correction, some sharpening, a slight contrast and clarity increase, and a slight color correction to neutralize the background sky.

However, I did not apply any luminance noise reduction. So all the images are noisier than what they would be in a final processed image.

Even so, all look very good. And with similar performance.

All frames were shot with Long Exposure Noise Reduction (LENR) on, for an automatic dark frame subtraction by the camera. I saw no artifacts from applying LENR vs. shots taken without it.

The 6D and 6D MkII perhaps show a little less noise than the old 5D MkII, as they should being newer cameras.

The 6D MkII also shows a little less pixelation on small stars, as it should being a 26 megapixel camera vs. 20 to 21 megapixels for the older cameras. However, you have to examine the images at pixel-peeping levels to see these differences. Nevertheless, having higher resolution without the penalty of higher noise is very welcome.


3 Canons at ISO 1600
The three cameras compared at ISO 1600. Note the histogram and region of the frame we are examining up close.

3 Canons at ISO 3200
The three cameras compared at ISO 3200. Note the histogram and region of the frame we are examining up close.

3 Canons at ISO 6400
The three cameras compared at ISO 6400. Note the histogram and region of the frame we are examining up close.
Above, I show images from the three cameras side by side at ISOs 1600, 3200, and 6400. It is tough to tell the difference in noise levels, the key characteristic for this type of astrophotography.

The new 6D MkII shows very similar levels of noise to the 6D, perhaps improving upon the older cameras a tad.

Because images are well-exposed (note the histogram at right), the 6D MkII is showing none of the flaws of its lower dynamic range reported elsewhere.

That’s the key. The 6D MkII needs a well-exposed image. Given that, it performs very well.


3 Canons Stacked & Processed
The three cameras in stacked and processed final images.
This version shows the same images but now with stacked frames and with a typical level of processing to make a more attractive and richer final image. Again, all look good, but with the modified camera showing richer nebulosity, as they do in deep-sky images.

The lead image at the very top is a final full-frame image with the Canon 6D MkII.


As such, based on my initial testing, I can recommend the Canon 6D MkII (and plan to use it myself) for deep-sky photography.

Indeed, I’ll likely have the camera filter-modified to replace my vintage yet faithful 5D MkII for most of my deep-sky shooting. The 6D MkII’s tilting LCD screen alone (a neck, back, and knee saver when attached to a telescope!) makes it a welcome upgrade from the earlier cameras.

The only drawback to the 6D MkII for deep-sky work is its limited dark frame buffer. As noted in my earlier review, it can shoot only three Raw files in rapid succession with Long Exposure Noise Reduction turned on. The 5D MkII can shoot five; the 6D can shoot four. (A 6D MkIIa should have this buffer increased to at least 4, if not 8 images.)

I make use of this undocumented feature all the time to ensure cleaner images in long deep-sky exposures, as it produces and subtracts dark frames with far greater accuracy than any taken later and applied in post-processing.


I hope you’ve found this report of interest.

With the 6D MkII so new, and between smoky skies and the interference of the Moon, I’ve had only one night under dark skies to perform these tests. But the results are promising.

For more tips on deep-sky imaging and processing see my pages on my website:

Ten Tips for Deep-Sky Images

Ten Steps to Deep-Sky Processing

Thanks and clear skies!

— Alan, September 7, 2017 / © 2017 Alan Dyer / amazingsky.com

 

Totality over the Tetons — the Music Video


Totality over Tetons Title Image

I present the final cut of my eclipse music video, from the Teton Valley, Idaho.

I’ve edited my images and videos into a music video that I hope captures some of the awe and excitement of standing in the shadow of the Moon and gazing skyward at a total eclipse.

Totality over the Tetons from Alan Dyer on Vimeo.

The video can be viewed in up to 4K resolution. Music is by the Hollywood session group and movie soundtrack masters, Audiomachine. It is used under license.

Eclipse Triumph Selfie (Wide)
Me at the 2017 total solar eclipse celebrating post-eclipse with four of the camera systems I used, for close-up stills through a telescope, for 4K video through a telephoto lens, and two wide-angle time-lapse DSLRs. A fifth camera used to take this image shot an HD video selfie.
Never before have I been able to shoot a total eclipse with so many cameras to capture the scene from wide-angles to close-ups, in stills, time-lapses, and videos, including 4K. Details on the setup are in the caption for the video on Vimeo. Click through to Vimeo.

I scouted this site north of Driggs, Idaho two years earlier, in April 2015. It was perfect for me. I could easily set up lots of gear, it had a great sightline to the Grand Tetons, and a clear horizon for the twilight effects. And I had the site almost to myself. Observing with a crowd adds lots of energy and excitement, but also distraction and stress. I had five cameras to operate. It was an eclipse experience I’ll likely never duplicate.

If you missed this eclipse, you missed the event of a lifetime. Sorry. Plain and simple.

2017 Eclipse Time Sequence Composite
A composite of the 2017 eclipse with time running from left to right, depicting the onset of totality at left, then reappearance of the Sun at right. Taken with the 4-inch telescope shown above.
If you saw the eclipse, and want to see more, then over the next few years you will have to travel far and wide, mostly to the southern hemisphere between now and 2024.

But on April 8, 2024 the umbral shadow of the Moon once again sweeps across North America, bringing a generous four minutes of totality to a narrow path from Mexico, across the U.S., and up into eastern Canada.

It will be the Great North American Eclipse. Seven years to go!

— Alan, September 2, 2017 / © 2017 Alan Dyer / www.amazingsky.com