How much better is the Canon EOS R6 III than previous models for astrophotography?

In a rare first for me, I actually used autofocus for this entire astrophotography shoot. If I'm being honest? I prefer it when shooting astro with a mirrorless camera. Why? Because it is quicker and that means more time capturing the stars and less time setting up. I can get a star in sharp focus using autofocus in half the time that it would take me to do it manually and it's way easier to focus with the shutter or back button than play about with the focus ring, especially with cold fingers.

I only managed to get out under one clear sky to test the new R6 III but it was a wonderful session at my usual dark hill spot surrounded by a sea of stars and celestial shapes. After setting up my tripod, I was ready to start shooting, armed with the Canon 14mm f/1.4 and 45mm f/1.2 lenses.

If you are a seasoned astrophotographer, you will undoubtedly have started your craft by learning how to manually focus on stars to get them crisp and sharp in the frame. Everyone does. Whilst the manual focus (MF) versus autofocus (AF) debate continues within the community, the technology for low-light autofocusing capability has come a long way since mirrorless cameras were first introduced and the R6 III is physical proof of that.

The astrophotography

You only get the luxury of being able to do this if your camera is actually good at autofocusing in low light and for starry nightscapes. All three versions of the Canon EOS R6 feature a low-light autofocus range of -6.5 exposure value (EV), so they already have a strong baseline for shooting under dark skies. The Canon EOS R6 III features a higher resolution and advanced autofocus algorithms, so the AF system actually has more data to use and is better at using it.

I was able to capture bright objects easily and start shooting without having to spend ages using manual focus for each new shot. The autofocus was powerful enough to capture at least one star in each of my frames. I simply used autofocus on the brighter points of light in my composition, waited for the green box and then switched to manual to avoid any refocusing if I decided to recompose the shot.

Bright objects were the easiest to capture, with Jupiter, Pollux and Castor easily captured in the western sky. Light pollution washed out the contrast in this shot but it was the quickest autofocus because of the brightness of the objects.

The autofocus helped me capture a range of other constellations too. With the R6 III focusing on the bright star Arcturus, along with the rest of Boötes and Coma Berenices next to the Coma Star Cluster (Melotte 111).

The shape of Leo is recognisable and the autofocus captured the brightest star, Regulus, to bring the rest of the stars in the constellation into focus. You can even spot the Beehive Cluster (M44) in Cancer, to the right of the frame and it is fairly sharp in focus. Barring some minor star trailing from my lack of a star tracker, the stars are nicely in focus, including on minor objects like star clusters.

Using the 45mm lens, I got some close-ups of some quadrilateral shapes in the sky. Hercules' prominent trapezoidal keystone is visible and one of the corners, Zeta Herculis, was picked up by the autofocus. It is not exactly a bright star, with a magnitude of 2.88, but the R6 III picked it up easily and brought the rest of the corners into focus. Whilst barely a smudge along one of the sides of Hercules, I even managed to capture the Hercules globular cluster (M13) with the R6 III and the Canon RF 45mm wide open at f/1.2.

The polygonal head of the dragon in Draco was easily captured in the centre of the frame, with bright stars Eltanin (2.23), Rastaban (2.79) and even Iota Herculis (3.8) showing prominently. The autofocus capabilities of the EOS R6 III are maximised when used alongside a lens with a very fast aperture like f/1.4 and f/1.2. Without these types of lenses, you would be much less likely to be able to autofocus on such dim stars.

The upgrades

The big question when looking at the third iteration of a camera model is to figure out if the upgrades are actually worth it. First, you have to think about your budget and also what you are using the camera for. For astrophotography, there are a few upgrades in the EOS R6 III that can be considered to see whether they are worth it.

The most noticeable upgrade on the R6 III is the resolution, which has been upgraded from the R6 II's 24.2MP sensor to a 32.5 MP sensor. On top of improved resolution for general and astrophotography, the boosted number of pixels allows the Dual Pixel CMOS AF II to collect even more data points because there are more pixels. Dual Pixel architecture splits each pixel into two separate photodiodes and allows each photodiode to read the light from the star at two different positions and allows the lens motor to bring those points together into perfect focus.

The upgraded sensor resolution combined with upgraded tracking algorithms from the flagship Canon EOS R5 II make the R6 III better at locking onto low-light points and make autofocus for astrophotography much more reliable than in previous models.

I initially expected the higher resolution to translate into more image noise on photographs but this was not the case. The R6 III utilizes dual-gate gain architecture, which means that every pixel has a switchable path at the hardware level depending on the ISO level used and allows images with higher ISOs to have a heavily reduced base amount of noise and thus makes them less grainy.

Photos at lower ISOs on the R6 III have an incredibly high dynamic range (HDR) thanks to the low conversion gate (LCG) circuit. This allows the natural color of the stars to be preserved instead of coming across as indeterminate white blobs, as well as the subtle hues of the dark surrounding sky in the photograph.

Aside from the technical aspects of how the resolution improves the autofocus, the detail in images from the R6 III is noticeable and is great for picking up finer stellar structures such as star clusters and smaller stars. When paired with a distorted lens like the Canon RF 7-14mm f/2.8-3.5 fisheye lens, extra resolution really helps details pop. I didn't get to use the fisheye lens for astro but general daytime shooting delivered some high-quality photographs.

The final important upgrade on the R6 III is the inclusion of a CFexpress card slot, which allows faster writing and reading speeds both in camera and during media downloads. A UHS-II SD card has an average read speed of 300MB/s and an average write speed of 260MB/s.

This may seem fast but the most advanced CFexpress cards have a read and write speed of over 3000MB/s, which makes huge workloads so much easier to process. This may only be of benefit to professional photographers who shoot a lot of video or need to do a huge amount of burst photography in RAW format, but it does vastly improve the performance of this camera. Bear in mind that CFexpress cards are much more expensive than SD cards and require an additional CFexpress reader to transfer data to a computer.

Is it worth it?

The price difference between the R6 Mark II and the Mark III is just under $1000 and for that amount of money, justifying the move up to the latest model comes down to a few factors that you will have to consider. The power of the low-light autofocus is tempting but you should think about the camera as a whole to see whether it is worth making the investment.

If you are looking to boost resolution in your night-time scenes and have been shooting astrophotography for a long time, the R6 III could be worth the extra investment thanks to the 32.5MP sensor, which retains the powerful dual-gain architecture for getting high dynamic range images at lower ISOs and delivering high ISO images with significantly less grain.

If you have a heavy workflow, you are likely to be frustrated with the lack of a CFexpress card slot on the earlier R6 models and would benefit from the advanced functionality the new slot will give you, especially if you shoot a lot of RAW imagery and video.

Stick with an earlier model or a different mirrorless camera if you are a very casual astrophotographer who does most of your shooting in the daytime. I just can't justify the massive jump in price for basic shooting, where a beginner or intermediate photographer's money might be better spent on getting a fast f/1.4 lens for superior astro. I used the Canon RF 14mm f/1.4 lens for astrophotography testing and I don't think the images would have looked half as good if I had used a lens with a smaller aperture. If you already own the R6 II, the only reason you might upgrade is if you need to do more heavy cropping into your images or need better hybrid video functionality from a camera.