Canon RF 10-20mm f/4 L IS STM – Review

In this post I’ll be reviewing the new Canon RF 10-20mm f/4 L IS STM made for Canon RF mount cameras like the EOS R5 that I’ll be using to test the lens with.

Overall, this is a great little lens. I really enjoyed shooting with it so read on to see my impressions including (just a couple) of the negatives…

Physical Aspects

Physically this lens is much smaller and lighter than past FULL FRAME ultra-wide-angle lenses with an f/4 aperture.

Here is chart showing the physical size and weight of this new RF lens compared to older EF equivalents.

Clearly, the new Canon RF 10-20mm f/4 L is saving a lot of weight which is going to make it a lot nicer to carry around on hikes or to keep in your bag in case you need an ultra-wide lens.

Handling & Usage

Being relatively light means that carrying and using this lens is pretty painless. It balances well on the camera and would be a good option for someone who has wrist pain who still wants to shoot full frame with a lens like this.

The lens is easy to use although the focus ring and the control ring are a little too close together. It’s very easy to accidentally turn one by accident when trying to turn the other. The zoom ring is smooth and easy to turn. All the rings are tightly fitted with no play in them.

One downside of this lens is that it won’t take a front filter. This isn’t a huge problem, but it does mean being more careful with the lens and keeping a dust cloth handy to do spot cleans here and there. Instead of a front filter there is a slot in the back where a rear filter can be inserted.

Speaking of cleaning the lens, it is one of the most difficult to clean lenses I have used as the front element is a bit of a dust magnet. And it’s necessary to keep the lens sparkling clean to achieve maximum image quality from the lens as it is very sensitive to oil and dust.

This lens has a unique lens cap which fully covers the lens hood and locks in using threads on the inside of the built-in lens hood. While the lens hood is nice and has a design which works better than some other lenses with large front elements like this, it is still an odd lens cap because it is more than an inch thick which is a big difference from most lens caps which are less than a quarter of an inch thick. It’s minor but it makes sticking the lens cap in a pants pocket pretty annoying.

There is also a button on the lens that can be assigned a specific function. I don’t know if that is camera body specific or if the lens keeps the assigned function from body to body.

Optical Image Stabilization

The RF 10-20mm f/4 L IS STM also has built in optical image stabilization.

The stabilization for stills is good but not quite exceptional on my R5. I have found that around a 1/4th of a second I have to take 3-5 shots to get a sharp one. But that was with mechanical shutter. With electronic shutter it seemed like I was getting sharp photos in 1-3 shots. The problem for me is that on the R5 the electronic shutter is limited to a max time of 1/2 a second. Shooting with a 1/2 second exposure is still impressive though and makes handheld shooting in almost total darkness a possibility.

Shooting video, the stabilization is pretty solid but if you want really smooth footage a gimbal or camera cage with handles is still necessary. This is probably the best I have used for just straight up handheld video though. I think it might even be slightly better than the RF 24-240mm which is tripod like at 24mm.

Zoom Range

The zoom range of this lens is 10-20mm, which may be limiting to some users who want to be able to shoot ultra-wide and zoom in to 24mm or even 35mm. It is truly an “ultra-wide zoom”.

Even though it may seem limiting to be stuck with just 10-20mm, the resolution at 20mm is high enough that cropping is not an issue. And the center of frame performance should make this lens a great performer on APS-C.

Bottom line, if you absolutely must have more magnification then using this lens on an APS-C will give you that. It’s not the perfect solution but it’s worth considering as APS-C cameras are getting better and better.

Focusing

Focusing is ok with this lens. It’s fast enough for most stills and quieter than most lenses too. It is reliable but does seem to just barely pull focus a lot especially when focusing center of frame. I did not extensively test tracking AF on my R5 but it is able to pick out a human subject even when at 10mm. The focus is not as snappy as most USM lenses, so it is a little slow to rack focus. I noticed a couple of times it focused behind a moving subject when I was using face tracking. Video shooters won’t care as much about snappy focus pulls so this lens should meet their expectations.

Distortion

Optically the lens is a good performer with some caveats. The first being that it has a lot of distortion at 10mm. To be fair, its less distortion, and more just not fully covering the sensor. This means the lens has to have digital corrections enabled for the image to be full 35mm frame size. Again, it’s one of those things that they have sacrificed to make the lens smaller, lighter, and probably, the price that it is. The good news is that the lens only exhibits barrel distortion, so the distortion correction is going to be simpler since there is no crossover from barrel into pincushion as many zoom lenses tend to have.

Below is an interactive example showing only the distortion correction at 10mm.

As you can see, the distortion correction is pretty substantial. Sharpness is visibly affected by the stretching required but only large prints will show obvious losses in resolution.

If you are shooting video the distortion correction will always be activated.

The reality is that despite the corrections this lens still manages to hang with the old EF 11-24mm f/4 L for about $700 less money.

Sharpness

I noticed some very slight sharpness inconsistency across the frame on the R5. To be fair, if I got lucky with focus the sharpness is good everywhere, but if the focus is ever so slightly off, I did notice some areas of softness here and there in the frame.

The problem with this is it’s very, very hard to see the focus is slightly off by looking through the viewfinder. What I found is that I typically want to focus to the left side of the frame rather than the center of the frame. I don’t know why that is, it could be how I hold the camera or how I tend to move when pressing the shutter button.

At higher shutter speeds it does seem to look sharper across the frame, so I think this is probably more of a stabilization issue.

Conclusion

This is a good lens that performs well and is lightweight. It is not that expensive for what it can do in the form factor that it has. Remember, this is a full frame lens that is similar in size to many APS-C lenses of the same type. Overall image quality is good but not flawless. It’s a nice lens to own if you’re willing to plunk down the money for it. Videographers in the market for an ultra-wide for Canon should like this one. It performed well for that purpose in the testing I did.

Image Samples