Canon RF 10-20mm F4 L IS STM Review: The Widest Autofocus Full-Frame Zoom
10mm on full frame is very wide. The Canon RF 10-20mm F4 L IS STM, announced in October 2023 at $2,299, is the widest rectilinear autofocus zoom you can buy for a full-frame camera. It replaces the EF 11-24mm f/4L at half the weight: 570 grams.
It’s also the first L lens with an STM focus motor, which Canon chose for smooth, quiet video focusing. Optical stabilization is rated at 5 stops, or 6 when combined with in-body stabilization, and a Peripheral Control IS mode reduces the wobble at the edges of the frame that wide lenses show in handheld video.
Lenses this wide are for tall buildings in tight streets, cathedral fronts you can’t step back from, and interiors where every meter counts.
Photo: Media Gallery
Gordon Laing’s first-look video, made with a pre-production sample, shows what 10mm looks like in practice.
Video review: Gordon Laing (first looks)
Design and the filter problem
The optical formula is 16 elements in 12 groups, with one Super UD, three UD and three aspherical elements. The aperture has nine blades, and PetaPixel and OpticalLimits both liked the sunstars it produces when you stop down.
The bulging front element means there’s no front filter thread. The hood is built in, and the only filter option is a gel slot at the rear of the lens. PetaPixel, Digital Camera World and Camera Labs all found that awkward. Landscape shooters who rely on ND grads and polarizers need a large third-party holder or a different lens.
Close focus is 0.25 meters. The lens is weather sealed with a fluorine coating on the front element. There’s a customizable control ring and a lens function button, which can be set to AF functions, pre-recording or zebras on supported bodies.
How it performs
The center is sharp from f/4, and reviewers found it good across most of the frame. The extreme corners are softer, as OpticalLimits and Fstoppers noted. Uncorrected distortion is heavy, measured at 9.2% barrel at 10mm by OpticalLimits, and vignetting is strong at 10mm. The camera corrects both, but you lose a little of the edge when it does. PetaPixel and OpticalLimits also saw some ghosting and flare.
Autofocus is silent and smooth, which Digital Camera World and Fstoppers liked for video and gimbal work.
Who it’s for
Architecture, interior and real-estate photographers, astrophotographers who want the widest field, and video shooters who need a very wide view on a gimbal. Price is the main objection, and every review raised it.
If you don’t need 10mm, the RF 14-35mm f/4L costs about half as much and takes front filters. The Canon RF 16-28mm F2.8 IS STM is cheaper again and a stop brighter. On Canon APS-C, the RF-S 10-18mm gives a similar 16mm-equivalent view for a fraction of the price. It suits high-resolution bodies like the Canon EOS R5 Mark II.