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.
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
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.
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.
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.
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!
In a technical blog I compare the new Canon 6D Mark II camera with its predecessor, the Canon 6D, with the focus on performance for nightscape astrophotography.
No pretty pictures in this blog I’m afraid! This is a blog for gear geeks.
The long-awaited Canon 6D Mark II camera is out, replacing the original 6D after that camera’s popular 5-year reign as a prime choice among astrophotographers for all kinds of sky images, including nightscapes and time-lapses.
As all new cameras do, the 6D Mark II is currently fetching a full list price of $2000 U.S. Eventually it will sell for less. The original 6D, introduced in 2012 at that same list price, might still be available from many outlets, but for less, likely below $1500 US.
Shown on the left, above, the 6D Mark II is similar in size and weight to the original 6D.
However, the new Mark II offers 6240 x 4160 pixels for 26 megapixels, a bump up in resolution over the 5472 x 3648 20-megapixel 6D. The pixel pitch of the Mark II sensor is 5.7 microns vs. 6.6 microns for the 6D.
One difference is that the port for a remote release is now on the front, but using the same solid 3-pin N3 connector as the 6D and other full-frame Canons. That makes it compatible with all external controllers for time-lapse shooting.
TESTING FOR THE NIGHT
My interest is in a camera’s performance for long-exposure astrophotography, with images taken at high ISO settings. I have no interest in auto-focus performance (we shoot at night with focus set manually), nor how well a camera works for high-speed sports shooting.
To test the Mark II against the original 6D I took test shots at the same time of a high-contrast moonlit scene in the backyard, using a range of ISO speeds typical of nightscape scenes.
The comparisons show close-ups of a scene shown in full in the smaller inset screen.
The key characteristic of interest for night work is noise. How well does the camera suppress the noise inherent in digital images when the signal is boosted to the high ISO settings we typically use?
This set shows the 6D MkII at five ISOs, from ISO 1600 all the way up to the seldom-used ISO 25,600, all shot in Raw, not JPG. In all cases, no noise reduction was applied in later processing, so the results do look worse than what processed images would.
Click or tap on all images to expand each image to full screen for closer inspection.
This set shows the same range of ISOs with the original 6D. All were taken at the same aperture, f/2.8, with a 35mm lens. Exposures were halved for each successive bump up in ISO speed, to ensure equally exposed images.
Comparing the sets, the 6D MkII shows a much greater tendency to exhibit a magenta cast in the shadows at very high ISOs, plus a lower contrast in the shadows at increasing ISOs, and slightly more luminance noise than the 6D.
How much more noise the 6D MkII exhibits is demonstrated here.
To me, visually, the MkII presents about 1/2 stop, or EV, worse noise than the 6D.
In this example, the MkII exhibits a noise level at ISO 3200 (a common nightscape setting) similar to what the 6D does if set between ISO 4000 and 5000 – about 1/2 stop worse noise.
Frankly, this is surprising.
Yes, the MkII has a higher pixel count and therefore smaller pixels (5.7 microns in this case) that are always more prone to noise. But in the past, advances to the in-camera signal processing has prevented noise from becoming worse, despite increasing pixel count, or has even produced an improvement in noise.
For example, the 2012-vintage 6D is better for noise than Canon’s earlier 2008-era 5D MkII model by about half a stop, or EV.
After five years of camera development I would have expected a similar improvement in the 6D MkII. After all, the 6D MkII has Canon’s latest DIGIC 7 processor, vs. the older 6D’s DIGIC 5+.
Instead, not only is there no noise improvement, the performance is worse.
That said, noise performance in the 6D MkII is still very good, and better than you’ll get with today’s 24 megapixel cropped-frame cameras with their even smaller 4 micron pixels. But the full frame 6D MkII doesn’t offer quite as much an improvement over cropped-frame cameras as does the five-year-old 6D.
In the previous sets all the images were well-exposed, as best they could be for such a contrasty scene captured with a single exposure.
What happens when Raw images are underexposed, then boosted later in exposure value in processing?
This is not an academic question, as that’s often the reality for nightscape images where the foreground remains dark. Bringing out detail in the shadows later requires a lot of Shadow Recovery or increasing the Exposure. How well will the image withstand that work on the shadows?
To test this, I shot a set of images at the same shutter speed, but at successively slower ISOs, from a well-exposed ISO 3200, to a severely underexposed ISO 100. I then boosted the Exposure setting later in Raw processing by an amount that compensated for the level of underexposure in the camera, from a setting of 0 EV at ISO 3200, to a +5 EV boost for the dark ISO 100 shots.
This tests for a camera’s “ISO Invariancy.” If a camera has a sensor and signal processing design that is ISO invariant, a boosted underexposed image at a slow ISO should look similar to a normally exposed image at a high ISO.
You’re just doing later in processing what a camera does on its own in-camera when bumping up the ISO.
But cameras that use ISO “variant” designs suffer from increased noise and artifacts when severely underexposed images are boosted later in Raw processing.
The Canon 6D and 6D MkII are such cameras.
This set above shows the results from the 6D Mark II. Boosting underexposed shadows reveals a lot of noise and a severe magenta cast.
These are all processed with Adobe Camera Raw, identical to the development engine in Adobe Lightroom.
This set above shows the results from the 6D. The older camera, which was never great for its lack of ISO Invariancy performance, is still much better than the new Mark II.
Effectively, this is the lack of dynamic range that others are reporting when testing the 6D MkII on more normal daytime images. It really rears its ugly head in nightscapes.
The lesson here is that the Mark II needs to be properly exposed as much as possible.
Don’t depend on being able to extract details later from the shadows. The adage “Expose to the Right,” which I explain at length in my Nightscapes eBook, applies in spades to the 6D MkII.
LONG EXPOSURE NOISE REDUCTION
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.
Here is the 6D Mark II in a pair of underexposed images at identical settings with LENR on and off. Not only did it not reduce noise and the magenta cast, using LENR made it worse.
This is so completely contrary to expectation that I wonder if the Mark II does not have a serious firmware issue in need of a fix in an upgrade.
DARK FRAME BUFFER
A unique feature of Canon full-frame cameras is that when LENR is on you can take several exposures in quick succession before the dark frame kicks in and locks up the camera. This is extremely useful for deep-sky shooting.
The single dark frame then gets applied to the buffered “light frames.”
The 6D Mark II, when in either Raw or in Raw+JPG can take 3 shots in succession. This is a downgrade from the 6D which can take 4 shots when in Raw+JPG. Pity.
ADOBE CAMERA RAW vs. DIGITAL PHOTO PROFESSIONAL
My next thought was that Adobe Camera Raw, while it was reading the Mark II files fine, might not have been de-Bayering or developing them properly. So I developed the same image with both Raw developers, Adobe’s and Canon’s latest version of their own Digital Photo Professional (DPP).
Here I did apply a modest and approximately similar level of noise reduction to both images:
In ACR: Color at 25, Luminosity at 40, with Sharpness at 25
In DPP: Chrominance at 8, Luminosity at 8, with Sharpness at 2
Yes, DPP did do a better job at eliminating the ugly magenta cast, but did a much worse job at reducing overall noise. DPP shows a lot of blockiness, detail loss, and artifacts left by the noise reduction.
Adobe Camera Raw and/or Lightroom remain among the best of many Raw developers.
A new feature the 6D Mark II offers is the ability to shoot and stack images in-camera. It can either “Add” the exposure values, or, most usefully, “Average” them, as shown here.
Other newer Canon DSLRs also offer this feature, notably the 7D MkII, the 5D MkIV, the 5Ds, and even the entry-level 80D. So the 6D MkII is not unique. But the feature was not on the 6D.
Here’s the benefit.
The left image is a single exposure; the middle is an average stack of 4 exposures stacked in camera; the right image an average stack of 9 exposures, the maximum allowed.
Noise smooths out a lot, with less noise the more images you stack. The result is a single Raw file, not a JPG. Excellent!
While this kind of stacking can be done later in processing in Photoshop, or in any layer-based program, many people might find this in-camera function handy.
Except, as you can see, the sky will exhibit star trails, and not as well defined as you would get from stacking them with a “Lighten” blend mode, as all star trail stacking routines use.
So this averaging method is NOT the way to do star trails. The Mark II does not offer the Brighten mode some other new Canons have that does allow for in-camera star trail stacking. Again, a pity in a camera many will choose for astrophotography.
Nevertheless, the Average mode is a handy way to create foreground landscapes with less noise, which then have to be composited later with a sky image or images.
On the left, below, the Mark II has a nearly identical layout of buttons and controls to the 6D on the right. So owners of the older model will feel right at home with the Mark II. That’s handy, as we astrophotographers work in the dark by feel!
Of course the big new feature, a first for Canon in a full-frame camera, is the Mark II’s fully articulated screen. It flips out, tilts, and even flips around to face forward. This is super-great for all astrophotography, especially when conducted by aging photographers with aching backs!
And the screen, as with the entry-level cropped-frame Canons, is a touch screen. For someone who hasn’t used one before – me! – that’ll take some getting used to, if only in just remembering to use it.
And it remains to be seen how well it will work in the cold. But it’s great to have.
Like other late-model Canon DSLRs, the 6D MkII has a built-in intervalometer. It works fine but is useable only on exposures with internally set shutter speeds up to 30 seconds.
However, setting the Interval so it fires the shutter with a minimal gap of 1 second between shots (our usual requirement for night time-lapses) is tricky: You have to set the interval to a value not 1 second, but 2 to 3 seconds longer than the shutter speed. i.e. an exposure of 30 seconds requires an interval of 33 seconds, as shown above. Anything less and the camera misses exposures.
Why? Well, when set to 30 seconds the camera actually takes a 32-second exposure. Surprise!
Other cameras I’ve used and tested with internal intervalometers (Nikon and Pentax) behave the same way. It’s confusing, but once you are used to it, the intervalometer works fine.
Except … the manual suggests the only way to turn it off and stop a sequence is to turn off the camera. That’s crude. A reader pointed out that it is also possible to stop a time-lapse sequence by hitting the Live View Start/Stop button. However, that trick doesn’t work on sequences programmed with only a second between frames, as described above. So stopping a night time-lapse is inelegant to say the least. With Nikons you can hold down the OK button to stop a sequence, with the option then of restarting it if desired.
Also, the internal Intervalometer cannot be used for exposures longer than 30 seconds. Again, that’s the case with all in-camera intervalometers in other models and brands.
As with many other new Canons, the Mark II has a Bulb Timer function.
When on Bulb you can program in exposure times of any length. That’s a nice feature that, again, might mean an external intervalometer is not needed for many situations.
A new feature I like is the greatly expanded information when reviewing an image.
One of the several screens you can scroll to shows whether you have shot that image with Long Exposure Noise Reduction on or not.
Excellent! I have long wanted to see that information recorded in the metadata. Digital Photo Professional also displays that status, but not Adobe Camera Raw/Lightroom.
While this has been a long report, this is an important camera for us astrophotographers.
I wish the news were better, but the 6D Mark II is somewhat of a disappointment for its image quality. It isn’t bad. It’s just that it isn’t any better than than the older 6D, and in some aspects is worse.
Canon has clearly made certain compromise decisions in their sensor design. Perhaps adding in the Dual-Pixel Autofocus for rapid focusing in Movie Mode has compromised the signal-to-noise ratio. That’s something only Canon can explain.
But the bottom-line recommendations I can offer are:
If you are a Canon user looking to upgrade to your first full-frame camera, the 6D Mark II will provide a noticeable and welcome improvement in noise and performance over a cropped-frame model. But an old 6D, bought new while they last in stock, or bought used, will be much cheaper and offer slightly less noise. But the Mark II’s flip-out screen is very nice!
If you are a current 6D owner, upgrading to a Mark II will not get you better image quality, apart from the slightly better resolution. Noise is actually worse. But it does get you the flip-out screen. I do like that!
If you are not wedded to Canon, but want a full-frame camera for the benefits of its lower noise, I would recommend the Nikon D750. I have one and love it. I have coupled it with the Sigma Art series lenses. I have not used any of the Sony a7-series Mirrorless cameras, so cannot comment on their performance, but they are popular to be sure.
“No ocean of water in the world can vie with its gorgeous sunsets; no solitude can equal the loneliness of a night-shadowed prairie.” – William Butler, 1873
In the 1870s, just before the coming of the railway and European settlement, English adventurer William Butler trekked the Canadian prairies, knowing what he called “The Great Lone Land” was soon to disappear as a remote and unsettled territory.
The quote from his book is on a plaque at the site where I took the lead image, Sunset Point at Writing-on-Stone Provincial Park.
The night was near perfect, with the Milky Way standing out down to the southern horizon and the Sweetgrass Hills of Montana. Below, the Milk River winds through the sandstone rock formations sacred to the Blackfoot First Nations.
The next night (last night, July 26, as I write this) I was at another unique site in southern Alberta, Red Rock Coulee Natural Area. The sky presented one of Butler’s unmatched prairie sunsets.
This is “big sky” country, and this week is putting on a great show with a succession of clear and mild nights under a heat wave.
The waxing crescent Moon adds to the western sky and the sunsets. But it sets early enough to leave the sky dark for the Milky Way to shine to the south.
This was the Milky Way on Wednesday night, July 27, over Red Rock Coulee. Sagittarius and the centre of the Galaxy lie above the horizon. At right, Saturn shines amid the dark lanes of the Dark Horse in the Milky Way.
I’m just halfway through my week-long photo tour of several favourite sites in this Great Lone Land. Next, is Cypress Hills and the Reesor Ranch.
The summer Full Moon arcs low across the southern sky, mimicking the path of the winter Sun.
This is a project I had in mind for the last month, and hoped to capture at the July Full Moon. A clear, dry, and cooperative night provide the chance.
The still images are composites of 40 images of the Moon traveling across the sky from dusk to dawn, taken at 10-minute intervals. They are layered onto a blend of background images of the 10 p.m. dusk sky (left), 2 a.m. middle-of-the-night sky (middle), and 5 a.m dawn sky (right).
As a bonus, the 10 p.m. sky shows some dark crepuscular rays in the twilight, while at 2 a.m. the Moon was in light cloud and surrounded by iridescent colours. By 5 a.m. denser clouds were moving in to obscure the Moon.
I shot the still image composite (above) and time-lapse movie (below) to illustrate the low arc of a summer Full Moon. In summer (June or July) the Full Moon sits at a similar place near the ecliptic as does the Sun in winter near the December solstice.
From the northern hemisphere the low position of the winter Sun gives us the short, cold days of winter. In summer, the similar low position of the Full Moon simply gives us a low Full Moon! But it is one that can be impressive and photogenic.
The time-lapse movie uses all 400 frames of the moving Moon superimposed onto the same background sky images, but now dissolving from one to the other.
The movie is 4K in resolution, though can be viewed at a smaller resolution to speed up playback if needed.
For the technically minded:
The Moon disks in the time-lapse and still composite come from a series of short 1/15-second exposures, short enough to record just the disks of the bright Moon set against a dark, underexposed sky.
I took these shots every minute, for 400 in total. They are blended into the bright background sky images using a Lighten blend mode, both in Photoshop for the still image, and in Final Cut for the movie.
The background sky images are longer exposures to record the sky colours, and stars (in the case of the 2 a.m. image). They are blended with gradient masks for the still image, but dissolved from one to the other in the time-lapse movie.
I shot the frames with a 15mm full-frame fish-eye lens and Canon 6D, with the camera not moved during the 7-hour shoot.
The arch of the Milky Way mirrors the sweep of the Red Deer River on a magical night in the Alberta Badlands.
Images of the Milky Way arching across the sky are now iconic. They are almost always assembled from individual frames stitched together to make a seamless panorama.
From the northern hemisphere, spring is the best season to shoot such a panorama as the Milky Way then remains confined to the eastern sky.
Later in summer, when the Milky Way passes directly overhead, panoramas are still possible, but the Milky Way looks distorted. The process of mapping a round sky onto a rectangular image, as I show here, inevitably stretches out the Milky Way near the zenith.
Last Saturday, in search of the Milky Way during prime panorama season, I set up for the night at Orkney Viewpoint overlooking the Red Deer River in the Alberta Badlands north of Drumheller. There, the river performs a grand curve through the valley below.
Above, the Milky Way, often described as a river of stars, sweeps in mirror-image fashion above the earthly river.
The panorama above contains the reflection of stars – of the constellation of Delphinus in particular – in the smooth water on a windless night.
To the north at left, the Northern Lights put on a subtle show. While never spectacular to the eye, the camera records the aurora’s colour and forms that often elude the naked eye.
The display was brightest early in the evening – that’s 11 p.m. now in May at my latitude.
The display then faded in intensity before I shot the two panoramas about 1 a.m., but the last few frames of the time-lapse show a final burst of colour from a lone curtain reflected in the river.
This was a magical night indeed. And a rare one this spring with clouds more often the norm at night.
The next dark of the Moon coincides with summer solstice. So while the moonlight won’t interfere, critical for shooting the Milky Way, the glow of perpetual twilight at my latitude will. The Milky Way will be set in a deep blue sky.
By July’s dark of the Moon the Milky Way will be high overhead, making panorama arches tough to assemble. It looks like this might have been my one best night to capture such a scene this year. But it was a good one.
This post shows that same area of sky (here at top) also setting into the west. But that’s the only area of sky familiar to northern hemisphere stargazers.
Everything below Orion and Sirius is new celestial territory for the northern astronomer. Welcome to the fabulous southern hemisphere sky.
And to the autumn sky – From home it is spring. From here in the southern hemisphere summer is giving way to cool nights of autumn.
Straight up, at centre, is the faint Milky Way area containing the constellations of Puppis and Vela, formerly in the constellation of Argo Navis.
Below, the Milky Way brightens in Carina and Crux, the Southern Cross, where dark lanes divide the Milky Way.
At right, the two patches of light are the Large and Small Magellanic Clouds, satellite galaxies of our Milky Way.
The bright object at left is Jupiter rising over the Tasman Sea.
I shot this 360° panorama on March 31, 2017 from Cape Conran on the Gippsland Coast of Victoria, Australia, at a latitude of 37° South.
I’ve turned the panorama so Orion appears as we’re used to seeing him, head up and feet below. But here in the southern hemisphere the image below despicts what he looks like, as he dives headfirst into the west in the evening twilight.
The bright object here is the waxing crescent Moon, here in Taurus. Taurus is below Orion, while Sirius (the bright star at top) and the stars of Canis Major are above Orion.
This view above takes in more of Canis Major. Note the Pleiades to the right of the Moon.
Visiting the southern hemisphere is a wonderful experience for any stargazer. The sky is disorienting, but filled with new wonders to see and old sights turned quite literally on their heads!
It takes a dark spring night to see it well, but now lurking near Jupiter is a ghostly sky glow called Gegenschein.
This diffuse glow lies directly opposite the Sun. It is caused by sunlight reflecting off interplanetary dust particles in the outer solar system. They reflect light more effectively at the anti-Sun point where each dust particle is fully lit by the Sun.
Like the Sun, the Gegenschein moves around the sky along the ecliptic, moving about a degree from west to east from night to night. March and April provide good nights for seeing the Gegenschein as it then lies in an area of sky far from the Milky Way.
Even so, it is very subtle to the unaided eye. Look south at about 1 a.m. local daylight time.
However, this year, in early April the Gegenschein will be more difficult as it will then lie right on top of Jupiter, as that planet reaches its point opposite the Sun on April 7. Jupiter will then be superimposed on the Gegenschein.
The main image at top is a 7-image vertical panorama of the spring sky, from Corvus and Virgo above the horizon, up past Leo, into Ursa Major and the Big Dipper overhead. Spica lies below bright Jupiter, Arcturus in Böotes is at left, while Regulus in Leo is at right. The grouping of stars near centre is the Coma Berenices star cluster.
Earlier in the night, I shot the sky’s other main glow – the Milky Way, as the winter portion of the Milky Way around Orion set into the southwest.
But over in the west, at the right edge of the frame, is the Zodiacal Light, caused by the same dust particles that create the Gegenschein, but that are located in the inner solar system between us and the Sun.