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

 

The Night-Shadowed Prairie


The Night Shadowed Prairie

“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.

Big Sky Sunset at Red Rock Coulee

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.

Waxing Crescent Moon at Red Rock Coulee

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.

The Milky Way at Red Rock Coulee

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.

— Alan, July 27, 2017 / © 2017 Alan Dyer / amazingsky.com

 

Rivers of Earth and Sky


Shooting at Orkney Viewpoint

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.

Rivers of Earth and Sky
This is a stitch of 8 segments with the Sigma 20mm Art lens, in portrait mode, and Nikon D750. Each 30 seconds at f/2 and ISO 3200. Stitched with Adobe Camera Raw. Taken on a mild and moonless night, May 20, 2017.

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.

Aurora over Red Deer River
This is a stack of 4 x 15-second exposures for the ground to smooth noise, and one 15-second exposure for the sky, all with the 20mm Sigma lens at f/2.8 and Nikon D750 at ISO 3200. They were part of a 250-frame time-lapse.

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.

Lone Curtain of Aurora over Red Deer River
This is a stack of 84 x 15-second exposures for the ground to smooth noise, and one 15-second exposure for the sky, all with the 20mm Sigma lens at f/2.8 and Nikon D750 at ISO 3200. They were part of a 250-frame time-lapse.

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.

— Alan, May 24, 2017 / © 2017 Alan Dyer / amazingsky.com 

The Amazing Austral Sky


Panorama of the Milky Way Overhead

The latitude of 30° South is the magic latitude on Earth for seeing the Milky Way.

From that region of the world – southern Australia, central South America, southern Africa – the centre of the Galaxy passes overhead, and you see the view at top.

You see the galactic core glowing brightly at the zenith, and the arms of the Milky Way stretching off to the horizon on either side of the core – to Aquila at left, for the northern half of the Galaxy, and to Carina at right, for the southern half of the Galaxy. That area of the Galaxy is always below the horizon for viewers at northern latitudes.

The image below focuses in on just the southern portion of the Milky Way, framing what in Australia is called the “Dark Emu,” a constellation made of the dark lanes along the Milky Way, from his head at right in Crux, to his tail at left in Scutum.

The Dark Emu Overhead

This is the most amazing region of the Milky Way, and is worth the trip south of the equator just to see, by lying back and looking up. You can easily see we live in a vast Galaxy, and not in the centre, but off to one side looking back at the core glowing overhead.

I would say there are three sky sights that top the list for spectacle:

• A bright all-sky aurora

• A total solar eclipse

• and the naked eye view of the Galaxy with its centre overhead and its arms across the sky from horizon to horizon.

I’ve checked off two this year! One more to go in August!

— Alan, May 2, 2017 / © 2017 Alan Dyer / AmazingSky.com 

 

Farewell Winter Sky


Panorama of the Winter Sky in March

As we celebrate the official arrival of spring in the Northern Hemisphere, we bid adieu to the stars of winter.

This was the scene last night from my backyard, of Orion and the surrounding constellations of the winter sky setting into the southwest in the early evening. Each night they will set sooner and sooner, even as the nights continue to grow shorter and the Sun sets later.

By late April Orion will be gone from our Northern Hemisphere sky — he hangs around until well into May for sites south of the equator.

Panorama of the Winter Sky in March (with Labels)
A horizon-to-zenith panorama of the winter consellations on a March evening as they set into the southwest. Taken from home March 19, 2017. This is a panorama of 5 panels, each with the 20mm Sigma Art lens at f/2, and Nikon D750 at ISO 3200, for 25 seconds each. Stitched with Adobe Camera Raw.

In this version I’ve labeled the main characters in this winter hunting scene – including some of the deep-sky “Messier”  objects like M45, the Pleiades; M44, the Beehive star cluster; and M42, the Orion Nebula.

At the same time this year, we also say goodbye to Venus which has shone so brightly these last few months as an evening star. By this weekend, it will be lost from sight as it passes between Earth and the Sun.

Mercury Rising and Venus Descending (with Labels)
Mercury (left) and Venus (right and bright) shinng low in the evening twilight, on March 19, 2017. Mercury was then 2 weeks before greatest elongation while Venus was a week before inferior conjunction. So Mercury was rising into the evening sky while Venus was rapidly descending. This is a 7-image HDR stack of exposures from 2.5 seconds to 1.6-second at ISO 200 with the Canon 6D and with the Sigma 50mm lens at f/4.

Meanwhile, Mercury is rising into view in the evening twilight, in its best evening showing of the year from northern latitudes. The view below is also from March 19, with Mercury to the left of brighter Venus.

Over the next two weeks, look low in the west for a bright star amid the twilight. Mercury appears farthest from the Sun on April 1, the date of its “greatest elongation.”

Having Mercury in our evening sky is a sure sign of spring.

Leo and the Spring Stars Rising
Leo rising in the east along with the northern hemisphere spring stars. Numerous satellite trails are visible. I didn’t clone them out. This is a vertical panorama of 4 frames, with the 20mm Sigma Art lens at f/2 and 25 seconds at ISO 3200 with the Nikon D750. Stitched with PTGui using Transverse Equirectangular projection.

Another sign of spring is Leo the lion.

While Orion sets in the west, the stars of spring are rising in the east. The panorama above depicts the scene in the eastern sky these nights, as Leo rises below the Big Dipper.

The Big Dipper is at upper left, with its handle pointing down to Arcturus at bottom left. The Bowl of the Dipper points down to the right to Regulus and the stars of Leo.

Above Leo is the star cluster M44, the Beehive, in Cancer. Below Leo at centre is the star cluster Mel 111, the Coma Berenices star cluster near the North Galactic Pole.

Happy Equinox! 

— Alan, March 20, 2017 / © 2017 Alan Dyer / amazingsky.com

 

 

The Ghostly Glow of Gegenschein


Northern Spring Sky Panorama

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.

Orion over the Old Barn

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.

The Zodiacal Light is better depicted in images in my previous post from Dinosaur Park

We bid adieu to the winter Milky Way now. As it departs we are left with an evening sky without the Milky Way visible at all. As seen from northern latitudes it lies along the horizon.

But later in spring, late at night, we’ll see the summer Milky Way rising, beginning its seasons of prominence until late autumn.

— Alan, March 19, 2017 / © 2017 Alan Dyer / AmazingSky.com 

 

A Starry Night in the Badlands


Winter Milky Way Arch and Zodiacal Light

In a winter of cloud, the skies cleared for a magical night in the Alberta Badlands.

Two weeks ago, on February 28, I took advantage of a rare and pristine night to head to one of my favourite spots in Dinosaur Provincial Park, to shoot nightscapes of the winter sky over the Badlands.

A spate of warm weather had melted most of the snow, so the landscape doesn’t look too wintery. But the stars definitely belong to winter in the Northern Hemisphere.

The main image above shows the winter Milky Way arching across the sky from southeast (at left) to northwest (at right). The tower of light in the west is the Zodiacal Light, caused by sunlight reflecting off dust particles in the inner solar system. It is an interplanetary, not atmospheric, effect.

Winter Sky Panorama at Dinosaur Park (Fish-Eye View)
This is a stitch of 6 segments with the 12mm Rokinon lens at f/2.8 for 30 seconds each, with the Nikon D750 at ISO 6400, mounted portrait. Stitched with PTGui.

Above, this 360° version of the scene records the entire sky, with the winter Milky Way from horizon to horizon. With a little averted imagination you can also trace the Zodiacal Light from west (right) over to the eastern sky (left), where it brightens in the diffuse glow of the Gegenschein, where dust opposite the Sun in the outer solar system reflects light back to us.

Winter Sky Panorama at Dinosaur Park (with Labels)
This is a stitch of 6 segments taken with the 12mm full-fame fish-eye Rokinon lens at f/2.8, all 30-second exposures with the Nikon D750 at ISO 6400. The camera was aimed portrait with the segments at 60° spacings. Stitched with PTGui using equirectangular projection with the zeith pulled down slightly.

A rectangular version of the panorama wraps the sky around from east (left), with Leo rising, to northeast (right), with the Big Dipper standing on its handle. I’ve added the labels in Photoshop of course.

Winter Stars over Dinosaur Park
This is a stack of 8 x 30-second exposures for the ground, mean combined to smooth noise, plus one 30-second exposure for the sky. All at f/2.2 with the Sigma 20mm Art lens and Nikon D750 at ISO 6400.

Here, in a single-frame shot, Orion is at centre, Canis Major (with Sirius) is below left, and Taurus (with Aldebaran) is at upper right. The Milky Way runs down to the south. The clusters M35, M41, M46 and M47 are visible as diffuse spots, as is the Orion Nebula, M42, below Orion’s Belt.

Evening Zodiacal Light at Dinosaur Park
The late winter evening Zodiacal Light, from at Dinosaur Provincial Park, Alberta, February 28, 2017. This is a stack of 7 x 30-second exposures for the ground, mean combined for lower noise, plus one 30-second exposure for the sky, all at f/2 with the 20mm Sigma Art lens, and Nikon D750 at ISO 6400.

This is certainly my best shot of the evening Zodiacal Light from my area in Alberta. It is obvious at this time of year on moonless nights, but requires a site with little urban skyglow to the west.

It is best visible in the evening from northern latitudes in late winter and spring.

Here, Venus is just setting above the badlands landscape. The Andromeda Galaxy is at right, the Pleiades at left. The Milky Way runs across the frame at top.

There is a common belief among nightscape photographers that the Milky Way can be seen only in summer. Not so.

What they mean is that the brightest part of the Milky Way, the galactic centre, is best seen in summer. But the Milky Way can be seen in all seasons, with the exception of spring when it is largely absent from the early evening sky, but rises late at night.

— Alan, March 14, 2017 / © 2017 Alan Dyer / AmazingSky.com