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

The Canon RF 10-20mm f/4 L IS STM is an ultra-wide zoom lens designed for use on the company’s R-series mirrorless cameras such as the Canon R5 and R6 II. It’s a full-frame lens, but it can also be used on APS-C format mirrorless cameras such as the Canon R7 and R10, on which it has an effective focal length of 16-32mm.

Naturally, the Canon RF 10-20mm f/4 L IS STM is seen as the RF-mount replacement for the EF 11-24mm f/4L USM which is designed for use on Canon DSLRs, but the new lens is significantly smaller and lighter. It also benefits from the RF mount’s large diameter and extra connection pins to deliver faster responses and better performance.

Like its predecessor, the RF 10-20mm f/4 L IS STM is an L-series lens which means it’s designed to withstand extensive use and deliver the results that professional photographers expect.

Enticingly, at the time of launch, the Canon EF 11-24mm f/4L USM is the widest full-frame lens with autofocus. It’s suitable for a range of uses such as landscape, architectural, and interior photography, and according to Canon, it outperform its EF-mount predecessor.

The lens comprises 16 elements in 12 groups, including aspherical and both UD (ultra-low dispersion) and Super UD glass elements. Canon has also applied anti-reflective coatings to reduce flare and ghosting.

Canon has used an advanced rectilinear design which enables a 130-degree angle of view with minimal distortion so that straight lines remain straight, even at the edges of the frame.

The lens uses an STM system for autofocusing, which is a first for Canon’s L-series. This is optimised for linear focus, which is good news for videography. The lens also features a positioning sensor, which eliminates the need for the lens to reset when the camera is powered on or off, making it slightly quicker to use. Full-time manual focusing is also available in case the focus needs a tweak.

There’s a closest focusing distance of 25cm throughout the focal length range. Focusing at this point delivers a magnifications of 0.12x at the 20mm end and 0.06x at the 10mm end.

As indicated by the ‘IS’, the RF 10-20mm f/4 L IS STM has built-in image stabilisation. In this instance it offers up to 5 stops of shake reduction, or up to 6 stops when paired with Canon’s R-series cameras that have in-body stabilisation (IBIS).

Additionally, the lens includes a new feature called Peripheral Control Image Stabiliser, which is basically a new algorithm designed to reduce motion blur at the edges of the frame. It’s especially useful for ultra-wide-angle shots and works in both video and stills mode.

While screw-on filters are not compatible due to the lens’s bulbous front element, a gelatine filter holder is present behind the rear element.

As you’d expect with a Canon L-series lens, the RF 10-20mm f/4 L IS STM is dust and water-resistant.

At 570g in weight and measuring 83.7 x 111mm, the RF 10-20mm f/4 L IS STM is 2cm shorter and 610g lighter than the Canon EF 11-24mm f/4L USM. It’s difficult to overstate the significance of this difference when the lens is in use. While the EF 11-24mm f/4L USM is bulky and front-heavy, the RF 10-20mm f/4 L IS STM is comparatively slim and well-balanced. It looks and feels good on a camera like the Canon R6 II and R5.

Left: Canon RF 10-20mm f/4 L IS STM, Right: Canon EF 11-24mm f/4 L USM

There are three rings around the barrel of the Canon RF 10-20mm f/4L IS STM. The ring closest to the front element and furthest from the camera, is the narrowest of the three and has a knurled texture. This is the dedicated control ring that can be customised to adjust a range of features such as the aperture, shutter speed or exposure compensation. Generally, I like to use it to adjust the exposure compensation directly, there’s also an option for it to only adjust the setting when it is used in conjunction with half-pressing the shutter button.

This ring has subtle click stops and can’t be de-clicked. Its movement feels good and doesn’t require too much or too little force.

Moving down the barrel, we come to the manual focus ring which moves smoothly and requires just the right amount of effort. Helpfully, this can be used to adjust the focusing manually even when the lens is switched to autofocusing.

Next in line is the zoom ring, which is broader than the other two and has a waist where the lens gets a little narrow towards the middle.

It takes less than a quarter turn to zoom from the 10mm point to the 20mm point and along the way there are markings for the 12mm, 14mm, 16mm and 18mm. The ridge covering on this ring is similar to that on the focusing ring and it gives an assured grip. It also falls at the point I automatically reach for when supporting the lens, with the two other rings within easy reach.

In addition to the lens rings, the RF 10-20mm f/4 L IS STM has a switch to turn the stabilisation on and off, and another to swap between manual and automatic focusing.There’s also a programable button which can be useful for things like stoping the focusing or shifting the focus to a specific distance.

I was invited to Canon’s UK headquarters to take a look at a pre-production sample of the RF 10-20mm f/4 L IS STM ahead of its announcement and as a wide-angle fan, I was excited to check it out. As the lens was a pre-production sample, I’m not able to give any in-depth analysis of its quality, but the early signs are very good and I can share a few images here.

It was a bright, breezy day which gave me the opportunity to test the lens’s resistance to flare and it seems very good. Chromatic aberration also appears to be kept under close control, and when mounted on a Canon EOS R5, the focusing is quick and decisive even in gloomy conditions.

The bright conditions meant the shutter speed was quite high, but I got a 100% hit rate when shooting at 1/4sec at the 10mm end. This enabled me to capture blur in the waving branches and leaves of a tree while the trunk is pin-sharp.

I need to shoot more images to be sure, but so far, vignetting doesn’t appear to be an issue.

It’s easy to forget just how wide 130° is, which means that you need to keep an eye on the edges of the frame, and often move closer to your subject to avoid empty areas of foreground. And if you’re shooting with the sun behind you, look out for your shadow in the image.

True to Canon’s claims, the RF 10-20mm f/4 L IS STM does render straight lines straight. Inevitably, there’s perspective distortion towards the edges of the frame, but that’s physics rather than a flaw closer object seem much larger than objects just a little further away.

Even at such a short focal length, it’s still possible to introduce some background blur by shooting at f/4. And conversely, closing down to f/16 or f/22 delivers a huge amount of depth of field so that very close and distant objects are acceptably sharp.

These images were shot using a pre-production sample of the Canon RF 10-20mm f/4 L IS STM on the Canon EOS R5

Canon has priced the RF 10-20mm f/4 L IS STM at less than the EF 11-24mm f/4L USM, and while the EF lens’ bigger size makes it look more impressive, the new RF optic is infinitely more user-friendly. It’s far better balanced on the camera as well as smaller and lighter. In fact its more than 50% lighter.

First impressions of the image quality are also very good. I need to put a full production sample through its paces before I can say for certain, but the Canon RF 10-20mm f/4 L IS STM seems like a high-quality lens that’s going to be attractive to landscape, architecture and interior photographers.