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The Canon R6 mirrorless camera promises good low-noise, low-light performance. Does it deliver for astrophotography? Credit: Canon

Canon’s Ra mirrorless camera, introduced in late 2019, was designed for deep-sky astrophotography and works very well. But after only two years on the market Canon has discontinued it. Unlike the Ra, the newer Canon R6 is not a modified camera (meaning it is not designed to record the deep red light of nebulas). 

However, with only 20 megapixels, low by today’s standards, the R6 should be ideal for most low-light astrophotography. I found that it is, but with some caveats and oddities most reviewers might not catch. 

NOTE: I tested an R6 purchased in June 2021 and updated in August with firmware v1.4. After completing the testing I updated the camera to firmware version 1.5 that was released on December 2, 2021. Sadly, it did not fix the amp glow issue reported below.

Live View framing

Mirrorless cameras present live views that show much more at night than do most DSLRs. However, the R6 also has a special trick to help frame nightscapes. Switch the Mode dial to Movie, and set the ISO up to 204,800 and the preview image brightens enough to show the Milky Way and dark foreground.

Andromeda Galaxy, M31, with Canon R6 (SS76) This demonstrates the R6’s deep-sky capabilities in a stack eight 8-minute exposures blended with a stack of shorter 2-minute exposures for the bright core.  Credit: Alan Dyer

While it’s meant just for aiming and framing, this super-sensitive mode makes the R6 a pleasure to use for framing nightscapes and deep-sky images. You can see the scene and the target. It is similar to the excellent but well-hidden Bright Monitoring mode on Sony alpha cameras. 

The back of the camera showing “live view” images from five cameras, showing how the R6 can match the Sony’s Bright Monitoring mode. Credit: Alan Dyer

 

Back of the camera in Movie Mode with the ISO topped out at 204,800 (on Auto here), the Milky Way shows up in Live View with a fast lens and the shutter at 1/8-second. Credit: Alan Dyer

Noise performance

On the R6’s 20-megapixel sensor, the individual pixels are each 6.6 microns in size, the “pixel pitch.” The larger the pixel pitch, the more photons each pixel can collect in a given amount of time. More photons equals more signal, and therefore a better signal-to-noise ratio. 

In noise tests comparing the R6 against the 30-megapixel Canon Ra and 26-megapixel Canon 6D Mark II DSLR, all three cameras showed a similar level of noise at ISO settings from 400 up to 12,800. But the 6D Mark II performed well only when properly exposed. Raising the shadows of underexposed 6D Mark II images reveals significant artifacts.

In nightscapes and deep-sky images the R6 and Ra looked nearly identical at each ISO setting. This was surprising considering the Ra’s smaller pixels, which perhaps attests to the low noise of the astronomical “a” model.

The progression of noise in a nightscape image. ISO 6400 is still good, with higher ISOs usable in a pinch if necessary. Credit: Alan Dyer

 

Comparison of noise at typical ISOs for deep-sky images. The Canon R6 and Canon Ra look similar, with the 6D Mark II a little worse, but not by much when exposed well. Credit: Alan Dyer

ISO invariance

The flaw in many Canon DSLRs (such as the 6D Mark II) is their poor dynamic range due to the lack of an ISO invariant sensor design. The R6, as with Canon’s other R-series mirrorless cameras, has addressed this weakness. The sensor in the R6 appears to be nicely ISO invariant and performs as well as the Nikon and Sony cameras I have tested, models praised for their ISO invariant behavior. (The links go to reviews on my blog of other cameras.)

Where this trait shows itself to advantage is on nightscapes where the starlit foreground is often dark and underexposed. Bringing out detail in the shadows in raw files requires a lot of Shadow Recovery or increasing the Exposure slider. Images from an ISO invariant sensor can withstand the brightening in post-processing far better, with minimal noise increase or degradation such as loss of contrast, added banding, or severe discolorations like those often shown by the 6D Mark II. The R6 performed very well for shadow recovery, making it an excellent nightscape camera.

Comparison of three Canon cameras in a blow-up of a dark nightscape scene. With the Canon 6D Mark II, underexposed shadows do not fare well when brightened. Credit: Alan Dyer

 

Six images with the R6, one well exposed (far left) and then underexposed by shooting at progressively lower ISOs, then each brightened in processing. The R6 shows good shadow recovery up to 4-stops underexposure. Credit: Alan Dyer

Star quality 

The R6 did not exhibit any oddities such as oddly colored or green stars, flaws that plague some Sony cameras, and Nikons when using Long Exposure Noise Reduction. I also saw no “star-eating,” a flaw Nikons and Sonys have been accused of over the years, due to aggressive in-camera noise reduction even on raw files, that results in fainter stars being wiped out.

Comparison of the Canon R6 and Ra imaging the Andromeda Galaxy using the same telescope. The 20-megapixel R6 does show slightly more pixelated stars than the 30-megapixel Ra, but the difference is not great. Credit: Alan Dyer

Edge artifacts and amp glow

The R6 did exhibit one serious and annoying flaw in long exposure images – a magenta glow along the edges, especially the right edge and lower right corner. 

Whether this is the true cause or not, it looks like “amplifier glow,” an effect caused by heat from circuitry illuminating the sensor with infra-red light. It shows itself when images are boosted in contrast and brightness during processing. It’s the sort of flaw revealed only when testing for the demands of astrophotography.

Amp glow is something I have not seen in Canon cameras for many years. Canon needs to fix this with a firmware update, as Sony did with a similar problem in their a7III.

This shows a This single raw image, with the contrast enhanced, brings out the magenta “amp glow” of the R6 on the right and lower edges. Credit: Alan Dyer

Turning on Long Exposure Noise Reduction (LENR, which automatically takes, and then subtracts, a “dark frame” from the previous exposure) eliminates the amp glow, as it should. But using LENR is not always practical, such as when taking time-lapses and star trails.

Red sensitivity

Compared to the factory-modified Ra with its boosted red sensitivity, the R6 did well at recording red nebulosity, but could not record the depth of nebulosity the Ra can, which is to be expected for a stock camera. 

In wide-field images of the Milky Way, the R6 picked up a respectable level of red nebulosity, especially when shooting through a broadband light pollution reduction filter, and when carefully processed. However, I would not recommend it for use with narrowband filters, as the R6 has good, but not sufficient, red sensitivity.

The magenta glow shows up in long nightscape images (left), but can be eliminated by shooting and applying a Long Exposure Noise Reduction (LENR) dark frame (right). Credit: Alan Dyer

 

For a stock “unmodified” camera, the R6 fared quite well in picking up red nebulosity in Cygnus nebulosity. Both the R6 and Ra images were shot through a broadband filter to reduce sky glow. Credit: Alan Dyer

Battery life

The R6 uses a new version of Canon’s standard LP-E6 battery, the LP-E6NH, that supports charging through the USB-C port and has a higher 2130mAh capacity than the 1800mAh LP-E6 batteries. However, the R6 is compatible also with older batteries.

On warm nights, I found the R6 ran fine on one battery for the 3 to 4 hours needed to shoot a time-lapse sequence, with power to spare.

The R6 accepts two memory cards, which can be identical, set up to record either the same files to both for backups or different files (such as stills and movies) to each. Credit: Alan Dyer

Video use

A major selling point for me was the R6’s low-light video capability. It replaces my Sony a7III, which had been my “go to” camera for real-time 4K movies of auroras. 

As best I can tell, the R6 performs as well as the Sony. It is able to record good quality (i.e. acceptably noise-free) 4K movies at ISO 25,600 to ISO 102,400. An example is here on Vimeo

The R6 can shoot at a shutter speed as slow as 1/8-second. That slow shutter speed and a fast f/1.4 to f/2 lens are the keys to shooting movies of the night sky. Unlike the R, Rp and Ra, the R6 records 4K movies from the full width of the sensor, making it possible to capture large swaths of sky with fast wide-angle lenses such as the TTArtisan lenses I tested for AstroGearToday here (11mm) and here (21mm).

A frame grab from a real-time movie (see below) of the Northern Lights taken November 4, 2021, shot at ISO 102,400. A lower, less noisy ISO would work for brighter auroras.  Credit: Alan Dyer

Missing features

The R6, like Canon’s low-end Rp, lacks a top LCD screen for display of camera settings and battery level. Without it, the R6 provides no indication of crucial battery level while a shoot is in progress, for example during a time-lapse. A top screen is also useful for checking ISO and other settings by looking down at the camera, as is usually the case when it is on a tripod or telescope. 

We are forced to rely on looking at the brighter rear screen for all information. Yes, it is a flip-out screen, so can be angled up for convenient viewing on a telescope. However, during a Bulb exposure this screen lights up with a readout of the elapsed time. While handy, it is overly bright and it cannot be dimmed or turned off, except by closing the screen, in which case the electronic viewfinder turns on to provide that same display. 

Either way, the timer display draws power needlessly when you most need to conserve it. It should be possible to completely turn off all displays. I’m happy to report that as of v1.5 firmware hitting the Info button now does turn off the Bulb Timer display.

When shooting long exposures on Bulb, either with the R6’s built-in Bulb Timer or controlled by an external intervalometer, the screen lights up with a timer readout. Credit: Alan Dyer

 

The Canon R6 accepts all new Canon RF lenses (such as the RF 15-35mm lens reviewed here) or older EF-mount lenses via an optional lens adapter. Credit: Alan Dyer

Conclusion

The bright live view image, low noise, and ISO invariant sensor of the R6 make it superb for nightscapes, apart from the nagging amp glow. That glow will also add an annoying edge gradient to deep-sky images, best dealt with when shooting by the use of LENR in camera or applying dark frames in processing. The other main deficiencies are the lack of a top screen and the overly bright rear screen, both inconveniences for astrophotography. 

For low-light movies the R6 is Canon’s answer to the Sony alphas. No other Canon camera can shoot night sky movies as well as the R6. For me, it was the prime feature that made the R6 the camera of choice to complement the Ra. 

And no, I have not tested a 45-megapixel Canon R5 to know from first-hand experience how it compares!

NOTE: This review is an edited version of a full-length and even more detailed review of the R6 that appears on the author’s blog at AmazingSky.net.

MSRP: $2,499
Website: www.usa.canon.com

About Alan Dyer

Alan Dyer is an astrophotographer and astronomy author based in Alberta, Canada. His website at www.amazingsky.com has galleries of his images, plus links to his product review blog posts, video tutorials, and ebooks on astrophotography.

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