Canon RF 16mm f/2.8 STM Review

Focus Speed and Performance

The Canon RF 16mm f/2.8 autofocuses quickly and accurately. This isn’t a surprise considering that ultra-wide lenses usually have more room for error (and less focus throw in general) compared to longer lenses, but it’s still welcome. There is some noise from the STM focusing motor, so video shooters may be better off with a lav mic rather than an on-camera shotgun mic.

Because of the f/2.8 maximum aperture, the Canon RF 16mm f/2.8 focuses well in dark conditions. Relative to an f/4 lens like the Canon RF 14-35mm f/4 L, you can focus with the 16mm f/2.8 if there’s half as much ambient light. The lens even has a pretty high maximum magnification of 0.26x, allowing for some interesting ultra-wide closeups and/or very near foregrounds without issue.

Distortion

This is where things start to look bad. The Canon RF 16mm f/2.8 has extreme levels of distortion: -11.71% barrel distortion by our tests! This is approaching fisheye level – in fact, I believe it sets a new record among all the non-fisheye lenses that we’ve tested.

Here’s a simulation of -11.71% barrel distortion on a flat grid:

A lens with this much distortion simply wouldn’t have been acceptable in the film days, but thanks to digital corrections, many photographers who shoot with the RF 16mm f/2.8 will never even notice how bad the distortion gets. Most post-processing software has corrections turned on by default, and if you shoot JPEG, Canon doesn’t even let you turn off the distortion corrections when you’re using this lens.

Unfortunately, correcting distortion to such a degree will inevitably stretch the pixels in your photo, especially in the corners, making them less sharp.

On the positive side, I’m happy to report that the Canon RF 16mm f/2.8 is a 16mm lens after the distortion has been fixed. Before corrections, it’s about as wide as a 15mm lens.

Vignetting

Where vignetting is concerned, this lens is extremely interesting. In photos where the distortion has not been corrected, the very tips of the corners are essentially black at f/2.8, as if there’s mechanical vignetting from a thick filter. Measuring this vignetting using our usual method in the lab is simply not productive, because you get measurements that show 10+ stops of vignetting.

However, like I said in the distortion section, the Canon RF 16mm f/2.8 simply isn’t meant to be used without fixing the distortion. Once the distortion is corrected, the dark tips of the corners are no longer shown in the photo, and the vignetting returns to reasonable territory. It’s still high, don’t get me wrong, but not unheard of. Here’s a full chart of our measurements, post distortion correction:

The maximum of 2.3 stops of vignetting is definitely high – you’ll need to correct it in a lot of your photos if you shoot at f/2.8. Also, the lens never reaches negligible vignetting levels, staying around 1.5 stops of vignetting even at the narrower apertures. As you focus more closely, things improve a bit, but only by about 1/3 stop at the most.

Here’s how the vignetting looks after correcting for distortion:

Lateral Chromatic Aberration

There is a Canon RF 16mm f/2.8 has a fair bit of chromatic aberration throughout the aperture range. Here’s the chart:

This is high enough that you’ll see chromatic aberration in a lot of your photos if you forget to enable corrections. While we occasionally see lenses with more CA than this, it’s definitely worse than average.

Here’s a real-world example of what happens when a high-contrast subject is in the corner of the frame. Let’s just ignore the fact that my tripod leg ended up in the photo here, too – or better yet, let’s pretend that it was deliberate!

Enabling the corrections in Lightroom works well, although there is still just a hint of lingering chromatic aberration that the software didn’t properly remove.

Sharpness

The Canon RF 16mm f/2.8 is not a very sharp lens, especially in the full-frame corners. Here’s how it measures in the lab:

The center is pretty good, and the midframes (APS-C corners) are at least reasonable. But the corners here are really bad, definitely in the bottom 10% of lenses that we’ve tested in Imatest.

For context, this is measured from a RAW file that did not have any distortion corrections applied, so the corner sharpness shown here would actually shrink a bit after stretching the corners when fixing distortion. Likewise, the portion of the RAW file examined for this test is where the corners will be after distortion correction – not the portion that’s cropped out after correcting distortion. All of that gave this lens the best chance to succeed. Unfortunately, the corners are just that bad.

I will say, however, that the copy of the Canon RF 16mm f/2.8 I tested had some noticeable decentering. I’ve requested a second copy of this lens to look for sample variation issues, and I will update this review with my findings once I’ve measured that copy in the lab. My prediction is that corner sharpness will be better on the second copy, although even a best-case scenario would put this lens well below average in corner sharpness.

By comparison, here’s how Canon’s RF 15-35mm f/2.8 L looks at its widest focal length of 15mm. It’s obviously a much more expensive lens and is far sharper; this is just for context. I’ll hold off on doing other lens comparisons until I’ve double checked the sharpness of the RF 16mm f/2.8 with a second copy.

Coma

Related to sharpness is coma, a lens aberration that makes points of light in the corner of a photo look like smears. Coma isn’t usually visible in everyday photography, but for something like Milky Way photography, it can be a factor. I was excited about the possibility of a portable 16mm f/2.8 lens for shooting the Milky Way, but how does it perform?

The crop shown after the image below is taken from the top-right corner of the Canon EOS R5 with the 16mm f/2.8. I didn’t do any resizing; it’s a direct excerpt from the image:

There’s definitely some coma here, and keep in mind that this is after distortion corrections have been applied, which jettisons the worst of the corners (although it does stretch what remains).

That said, let me point something out. The image above only looks bad – both soft and high in coma – near the top-right corner and corresponding edges. If you instead look in the direction of the image center, this crop actually doesn’t look too bad.

To me, this suggests that the Canon RF 16mm f/2.8 should be treated more as a pretty solid 18mm lens that can become a 16mm in a pinch if you don’t mind soft corners. Everywhere you look, from vignetting to sharpness, it’s really that last 3-5% of each corner that actually looks bad. The rest of the image, though far from best-in-class, is hardly bad.

In short, the coma result here is very revealing. Yes, it’s pretty noticeable in the extreme corners, but cropping even slightly makes things look substantially better.

Sunstars and Flare

Here’s one area where I have some mostly positive things to say about the Canon RF 16mm f/2.8 – it has good flare performance and sunstars in most images!

There is a bit less contrast and some rainbow-colored flare directly around the sun itself, at least in some photos, but the rest of the photo tends to look pretty good. I will say, it depends on the position of the sun. Here’s a worst-case and best-case photo of the same subject, the difference being a change in camera position that blocked the sun a little more. (No cloning or spot healing was applied to either photo):

That may seem like a big difference considering how similar the scene looks, but that was pretty typical of my experience with this lens. Here’s a similar, though less extreme example:

I would categorize the flare performance here as excellent when the sun is blocked just enough, but that there is a point where the sun can overwhelm the lens’s anti-flare coatings, and you get some noticeable issues.

In any case, even at its worst, the Canon RF 16mm f/2.8 is still better than a lot of ultra-wide lenses in terms of flare. At its best, its flare is almost best-in-class – and the well-defined 14-point sunstars are pretty nice.

The next page of this review sums up everything and explains the pros and cons of the Canon RF 16mm f/2.8. So, click the menu below to go to “Verdict”: