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 

 

Jasper by Starlight


Taurus Rising over Mount Kerkeslin

The annual Dark Sky Festival in Jasper National Park ended with the best finale – dark skies, on a beautiful star-filled night. 

On Saturday night, October 22, I left the final set of science talks in the Big Tent at the heart of the Festival and headed out down the Icefields Parkway for a night of shooting Jasper by starlight.

The lead image is of the winter stars, including the Pleiades, rising above Mt. Kerkeslin at Athabasca Falls.

Pleiades and Taurus over Athabasca Falls
The Pleiades star cluster and the other stars of Taurus rising above Mount Kerkeslin at Athabasca Falls, in Jasper National Park, Alberta, October 22, 2016. The sky is brightening with the rising waning Moon off frame at left. Some cloud adds star glows and hazy patches to the sky. This is a stack of 15 exposures, mean combined to smooth noise, for the ground and one exposure for the sky. All are 25 seconds at f/2 with the Sigma 20mm Art lens and Nikon D750 at ISO 6400.

I shot the image above moments later, from the usual viewpoint overlooking the Falls, reduced to a trickle in late autumn. Illumination is solely by starlight – no artificial and glaring light painting here.

Perseus and Cassiopeia over Mt Kerkeslin
The autumn constellations of Perseus, Cassiopeia and Andromeda over Mount Kerkeslin at the Athabasca River Viewpoint on the Icefields Parkway, in Jasper National Park, Alberta. The Andromeda Galaxy is at upper right. The Pleiades are just clearing the mountain top at lower right. Thin clouds add the natural glows around the stars. Illumination is from starlight. This is a stack of 8 exposures, mean combined to smooth noise, for the ground and one exposure for the sky, all 25 seconds at f/2 with the Sigma 20mm lens and Nikon D750 at ISO 6400.

Earlier in the night, I stopped at the Athabasca River Viewpoint and shot the autumn stars of Cassiopeia, Andromeda, and Perseus above Mt. Kerkeslin. The Pleiades are just appearing above the mountain ridge.

Stars over Athabasca River
The autumn stars of the watery constellations of Capricornus, Aquarius, Piscis Austrinus, and Cetus over the Athabasca River and the peaks of the Continental Divide, from the Athabasca River Viewpoint (the “Goats and Glaciers” viewpoint) on the Icefields Parkway, Jasper National Park, Alberta. Thin cloud provides the natural glows around the stars. This is a stack of 8 exposures for the ground, mean combined to smooth noise, and one exposure for the sky, all 25 seconds at f/2 with the Sigma 20mm Art lens, and Nikon D750 at ISO 6400.

From that viewpoint I shot a scene looking south over the river and with the stars of Capricornus and Aquarius above the Divide.

Milky Way over Athabasca Pass
The Milky Way over the region of Athabasca Pass, as seen from the highway viewpoint on the Icefields Parkway, in Jasper National Park, Alberta, Oct 22, 2016. The Milky Way here is the section through Aquila, with Altair at top and Mars bright above the peaks of the Continental Divide. This is a stack of 8 exposures, mean combined to smooth noise, for the ground and one exposure for the sky, all 25 seconds at f/2 with the Sigma 20mm lens, and Nkion D750 at ISO 6400.

At the start of the night I stopped at the viewpoint for Athabasca Pass far in the distance. The summer Milky Way was setting over the pass. This historic pass was used by David Thompson in the late 1700s and early 1800s as his route into B.C. to extend the fur trade across the Divide. Thompson writes in his Journal about one particularly clear night on the pass:

“My men were not at their ease, yet when night came they admired the brilliancy of the Stars, and as one of them said, he thought he could almost touch them with his hand.”

The night ended with a display of Northern Lights over the Athabasca River. What a superb night under the stars in Jasper!

Aurora over Athabasca River
The Northern Lights over the Athabasca River in Jasper National Park, Alberta, Canada, on October 22/23 at about 1:30 am. I shot this from an access point to the Athabasca River by the bridge on Highway 93 on the Icefields Parkway. Pyramid Mountain is at left near the town of Jasper. Vega is the bright star at left; the Big Dipper is at right. The image is a stack of 10 exposures for the ground, mean combined to smooth noise and to smooth the water, and one exposure for the sky and aurora. All 15 seconds at ISO 1600 at f2 with the Sigma 20mm lens and Nikon D750.

As a finale, here’s a music video collecting together still images and time-lapse movies shot this night, and on two other nights during the Dark Sky Festival, including at the big Lake Annette “Beyond the Stars” star party I spoke at.

Enjoy!

As usual, enlarge to full screen and go to HD for the best view.

Thanks!

— Alan, October 24, 2016 / © 2016 Alan Dyer / www.amazingsky.com

 

The Moving Stars of the Southern Hemisphere


Southern Sky Star Trails - OzSky Looking South

Nothing amazes even the most inveterate skywatcher more than traveling to another hemisphere and seeing sky move. It moves the wrong way!

Whether you are from the southern hemisphere traveling north, or as I do, travel south from the Northern Hemisphere, watching how the sky moves can be disorienting.

Here I present a video montage of time-lapses shot last April in Australia, at the annual OzSky Star Party near Coonabarabran in New South Wales.

Select HD and Enlarge button to view at full screen at best quality.

You’ll see the sky set in the west but traveling in arcs from right to left, then in the next clip, rise in the east, again moving from right to left. That’s the wrong angle for us northerners.

Looking north you see the seasonal constellations, the ones that rise and set over a night and that change with the seasons. In this case, the night starts with Orion (upside-down!) to the north but setting over in the west, followed by Leo and bright Jupiter. The sky is moving from east to west, but that’s from right to left here. The austral Sun does the same thing by day.

Looking south, we see the circumpolar constellations, the ones that circle the South Celestial Pole. Only there’s no bright “South Star” to mark the pole.

The sky, including the two Magellanic Clouds (satellite galaxies to the Milky Way) and the spectacular Milky Way itself, turns around the blank pole, moving clockwise – the opposite direction to what we see up north.

I shot the sequences over four nights in early April, as several dozen stargazers from around the world revelled under the southern stars, using an array of impressive telescopes supplied by the Three Rivers Foundation, Australia, for us to explore the southern sky.

I’ll be back next year!

– Alan, August 19, 2016 / © 2016 Alan Dyer / www.amazingsky.com

 

Capturing the Quadrantids


Quadrantid Meteor Shower Composite

The Quadrantid meteors streaked out of the northern sky on a fine winter’s night.

The temperature was mild and skies clear in the early evening for the annual Quadrantid meteor shower. This is a prolific but short-lived shower with a brief peak. The cold and low altitude of its radiant point keeps this shower from becoming better known.

This was the first year I can recall shooting it. I had some success during a 2-hour shoot on January 3, from 9 to 11 pm MST.

The result above is a stack of 14 images, the best out of 600 shot that recorded meteors. The ground and sky comes from one image with the best Quad of the night, and the other meteor images were masked and layered into that image, with no attempt to align their paths with the moving radiant point.

However, over the 2 hours, the radiant point low in the north would not have moved too much, as it rose higher into the northern sky.

Most of the meteors here are Quads, but the very bright bolide at left, while it looks like it is coming from the radiant, it is actually streaking toward the radiant, and is not a Quadrantid. But oh so close! I left it in the composite for the sake of the nice composition!

Light clouds moving in added the natural star glows around the Big Dipper stars.

All frames were 10 seconds at f/2 with the 24mm lens and Nikon D750 at ISO 3200.

— Alan, January 4, 2016 / © 2016 Alan Dyer / www.amazingsky.com 

Astrophotography Video Tutorials – Free!


 

Video Tutorial FB PR ImageLearn the basics of shooting nightscape and time-lapse images with my three new video tutorials.

In these comprehensive and free tutorials I take you from “field to final,” to illustrate tips and techniques for shooting the sky at night.

At sites in southern Alberta I first explain how to shoot the images. Then back at the computer I step you through how to process non-destructively, using images I shot that night in the field.


 

Tutorial #1 – The Northern Lights

This 24-minute tutorial takes you from a shoot at a lakeside site in southern Alberta on a night with a fine aurora display, through to the steps to processing a still image and assembling a time-lapse movie.


 

Tutorial #2 – Moonlit Nightscapes

This 28-minute tutorial takes you from a shoot at Waterton Lakes National Park on a bright moonlit night, to the steps for processing nightscapes using Camera Raw and Photoshop, with smart filters, adjustment layers and masks.


 

Tutorial #3 – Star Trails

This 35-minute tutorial takes you from a shoot at summer solstice at Dinosaur Provincial Park, then through the steps for stacking star trail stills and assembling star trail time-lapse movies, using specialized programs such as StarStaX and the Advanced Stacker Plus actions for Photoshop.

 

As always, enlarge to full screen for the HD versions. These are also viewable at my Vimeo channel.  

Or they can be viewed on my YouTube channel

Thanks for watching!

And for much more information about shooting and processing nightscapes and time-lapse movies, check out my 400-page multimedia eBook, linked below.

— Alan, November 21, 2015 / © 2015 Alan Dyer / www.amazingsky.com/tutorials.html

 

A Super Eclipse of the Moon


The Full Moon rises in partial eclipse over the sandstone formations of Writing-on-Stone Provincial Park in southern Alberta, on the evening of September 27, 2015. This was the night of a total lunar eclipse, which was in progress in its initial partial phase as the Moon rose this night. The blue band on the horizon containing the Moon is the shadow of Earth on our atmosphere, while the dark bite taken out of the lunar disk is the shadow of Earth on the Moon. The pink band above is the Belt of Venus. This is a two-image panorama stitched to extend the scene vertically to take in more sky and ground than one frame could accommodate. Both shot with the 200mm lens and 1.4x extender, on the Canon 5DMkII.

I could not have asked for a more perfect night for a lunar eclipse. It doesn’t get any better!

On Sunday, September 27, the Moon was eclipsed for the fourth time in two years, the last in a “tetrad” of total lunar eclipses that we’ve enjoyed at six-month intervals since April 2014. This was the best one by far.

The Full Moon rising in partial eclipse on the night of September 27, 2015, night of a total eclipse that began with the partial phase in progress at moonrise from my location. The pink Belt of Venus colours the sky at top. The Moon sits in the blue shadow of the Earth, which also partly obscures the disk of the Moon. I shot this from Writing-on-Stone Provincial Park, Alberta. This is through the TMB 92mm refractor for a focal length of 550mm using the Canon 60Da at ISO 400 for 1/250 second.
This is through the TMB 92mm refractor for a focal length of 500mm using the Canon 60Da at ISO 400 for 1/250 second.

The timing was perfect for me in Alberta, with the Moon rising in partial eclipse (above), itself a fine photogenic site.

In the top image you can see the rising Moon embedded in the blue band of Earth’s shadow on our atmosphere, and also entering Earth’s shadow on its lunar disk. This was a perfect alignment, as lunar eclipses must be.

For my earthly location I drove south to near the Montana border, to a favourite location, Writing-on-Stone Provincial Park, to view the eclipse over the sandstone formations of the Milk River.

The image below shows a screen shot of my site plan and viewing angles using The Photographer’s Ephemeris app.

IMG_2515

More importantly, weather forecasts for the area called for perfectly clear skies, a relief from the clouds forecast – and which did materialize – at home to the north, and would have been a frustration to say the least. Better to drive 3 hours!

This was the second lunar eclipse I viewed from Writing-on-Stone, having chased clear skies to here in the middle of the night for the October 8, 2014 eclipse.

Me, in a selfie, observing a total eclipse of the Moon with binoculars on September 27, 2015, from Writing-on-Stone Provincial Park, Alberta. I had three cameras set up to shoot the eclipse and a fourth to shoot the scene like this. The night was perfect for the eclipse. The Moon is in totality here, with the stars and Moon trailed slightly from the long exposure.

I shot with three cameras: one doing a time-lapse through the telescope, one doing a wide-angle time-lapse of the Moon rising, and the third for long-exposure tracked shots during totality, of the Moon and Milky Way.

The Moon in total eclipse on September 27, 2015 – the “supermoon” eclipse – shining red over the Milk River and sandstone formations at Writing-on-Stone Provincial Park in southern Alberta, with the Milky Way in full view in the sky darkened by the lunar eclipse. The Sweetgrass Hills of Montana are to the south. The centre of the Milky Way is at far right. The Andromeda Galaxy is at upper left. The Moon was in Pisces below the Square of Pegasus. It was a perfectly clear night, ideal conditions for shooting the eclipse and stars. This is a stack of 5 x 2-minute tracked exposures for the sky and 5 x 4-minute untracked exposures for the ground to smooth noise. The Moon itself comes from a short 30-second exposure to avoid overexposing the lunar disk. Illumination of the ground is from starlight. All exposures with the 15mm lens at f/2.8 and Canon 5D MkII at ISO 1600. The camera was on the iOptron Sky-Tracker.
This is a stack of 5 x 2-minute tracked exposures for the sky and 5 x 4-minute untracked exposures for the ground to smooth noise. The Moon itself comes from a short 30-second exposure to avoid overexposing the lunar disk. Illumination of the ground is from starlight. All exposures with the 15mm lens at f/2.8 and Canon 5D MkII at ISO 1600. The camera was on the iOptron Sky-Tracker.

That image is above. It shows the eclipsed Moon at left, with the Milky Way at right, over the Milk River valley and with the Sweetgrass Hills in the distance.

The sky was dark only during the time of totality. As the Moon emerged from Earth’s shadow the sky and landscape lit up again, a wonderful feature of lunar eclipses.

While in the above shot I did layer in a short exposure of the eclipsed Moon into the long exposure of the sky, it is still to accurate scale, unlike many dubious eclipse images I see where giant moons have been pasted into photos, sometimes at least in the right place, but often not.

Lunar eclipses bring out the worst in Photoshop techniques.

The total eclipse of the Moon of September 27, 2015, in closeup through a telescope, at mid-totality with the Moon at its darkest and deepest into the umbral shadow, in a long exposure to bring out the stars surrounding the dark red moon. This was also the Harvest Moon for 2015 and was the perigee Full Moon, the closest Full Moon of 2015. This is a single exposure taken through the TMB 92mm refractor at f/5.5 for 500 mm focal length using the Canon 60Da at ISO 400 for 8 seconds, the longest I shot during totality. The telescope was on the SkyWatcher HEQ5 mount tracking at the lunar rate.
This is a single exposure taken through the TMB 92mm refractor at f/5.5 for 500 mm focal length using the Canon 60Da at ISO 400 for 8 seconds, the longest I shot during totality. The telescope was on the SkyWatcher HEQ5 mount tracking at the lunar rate.

Above is a single closeup image taken through the telescope at mid-totality. I exposed for 8 seconds to bring out the colours of the shadow and the background stars, as faint as they were with the Moon in star-poor Pisces.

I shot a couple of thousand frames and processing of those into time-lapses will take a while longer, in particular registering and aligning the 700 I shot at 15-second intervals through the telescope. They show the Moon entering, passing through, then exiting the umbra, while it moves against the background stars.

Me celebrating a successful total eclipse of the Moon during the final partial phases, observed and shot from Writing-on-Stone Provincial Park, Alberta, on September 27, 2015. I shot with 3 cameras, with a 4th to record the scene. Two of the cameras at centre are still shooting time-lapses of final partial phases. The camera at right was used to take long tracked exposures of the Milky Way during totality. The telescope at left was used just to look!

So I was a happy eclipse chaser! I managed to see all four of the lunar eclipses in the current tetrad, two from Alberta, one from Australia, and one from Monument Valley.

With the latest success, I’ve had my fill of lunar eclipses for a while. Good thing, as the next one is not until January 31, 2018, before dawn in the dead of winter.

With the mild night, great setting, and crystal clear skies, this “supermoon” eclipse could not have been better. It was a super eclipse.

– Alan, September 29, 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!

This is a decidedly non-pretty-picture blog!

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.

NOTE: In case you think this difference arises only because of the lens, not the camera or sensor, I invite you to check the version of this review at my website page, where there are images taken with each camera shooting through the same optics, the telescope. They show the same difference due to the “ISO invariant” sensor in the Nikon vs. the “ISO variant” sensor in the Canon. 

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:

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, depending on whether it is controlled internally or externally, and on the length of exposure, the interval usually has to be no less than 3 to 4 seconds, which can lead to unsightly gaps in star trails.

Small Advantage: Canon


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.)

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.


You can read a slightly more complete version of this report at my website at

http://www.amazingsky.com/canon-vs-nikon.html

… where you can also download higher resolution versions of the test images for closer inspection.

My website version contains test images of the ISO Invariance difference on images of the Andromeda Galaxy, as well as comparison images of the Canon 24mm L-series lens vs. the Sigma 24mm Art lens.

All images and text are © 2015 Alan Dyer.

– Alan, August 27, 2015 & Revised August 28, 2015 / © 2015 Alan Dyer / www.amazingsky.com