Canon RF 28-70mm f/2L USM
by Aether in
Photography Tech

Last Updated on January 22, 2019 by Aether

Announced at the same time as the EOS R, the Canon RF 28-70mm f/2L USM is certainly the most talked about lens with its constant f/2 aperture that exceeds market standards. A real showcase of all Canon’s optical know-how.

Getting started

It weighs 1.43 kg, which for a trans-standard zoom is huge! We had already judged the 50 mm f/1.2L USM as being very heavy at 950 g and for comparison, the Tamron SP 24-70 mm f/2.8 Di VC USD G2 for SLR cameras weighs just over 900 g and the Sigma 24-70 mm f/2.8 DG OS HSM Art 1.025 kg in Canon mount, both with an integrated stabilisation system missing from the Canon RF 28-70mm f/2L USM.

Firstly let’s note the excellent manufacturing quality of the RF 28-70 mm f/2L USM. The design is simple, identical to that of the other models in the range with a black satin coating that does not catch dust and impeccable assembly of all parts. The different rings are easily accessible and offer a good grip. As close as possible to the drum is the one dedicated to adjusting the zoom. It has good friction and a short turning point allowing you to switch from one extreme to the other of the focal length range in about 1/6th of a turn.

Just above, a locking button fixes the lens to its shortest dimension, at 28 mm, for storage. On the other side, a selector switch allows you to switch between AF and MF modes. Above, the focus ring is identical to that of the zoom lens with a lower friction that makes it a little too fluid. But let’s face it, in practice we have made little use of it. The ability to quickly move the EOS R’s autofocus collimator over the entire sensor surface and the low-light performance of the autofocus system made the use of manual focusing unnecessary. It should be noted that this ring does not have a stop at its extreme values. No distance indication appears on the lens, but switching to manual focus automatically causes a distance scale to appear in the viewfinder. This absence is therefore in no way embarrassing, quite the contrary.

As close as possible to the front lens, the adjustment ring can be set via the device menu. As with the other RF objectives, we appreciated its use. Its coating is different from that of zoom and focus rings, so it is impossible to confuse them when you have your eye on the viewfinder. Given the weight of the lens, it is all the more useful here because it is always necessary to keep one hand on the lens when shooting.

The RF 28-70mm f/2L USM comes with a sun visor equipped with a locking system to ensure it stays in place. Its internal structure is striated but does not have a felt covering. In practice, it is difficult to say if this leads to any change because we have never suffered from a flare problem.

If the lens were not so heavy and cumbersome, it would certainly get the highest score in grip, but although its technical characteristics are exceptional, its dimensions go against easy handling.

In the field

The choice of the focal length range from 28 to 70 mm is a little surprising and could penalise this lens in a market usually composed of 24-70 mm zooms. In the field, this point was not very important, although we would sometimes have appreciated a slightly more open angle of view. Of course, a 24-70 mm constant aperture f/2 would have been even more cumbersome and certainly impossible to build. The field covered by this lens remains very versatile and its very wide field of application ranges from landscapes to portraits and building photos.

Its constant aperture at f/2 is brighter than that of an f/2.8 lens. In practice, the difference is not huge when it comes to shooting in low light, especially since the lack of stabilisation is rather penalising here: the stabilised 24-70 f/2.8 lenses make it possible to shoot with more comfort when the light is weaker. On the other hand, it is an advantage for the use of shallow depths of field and we have seen a real difference on the bokeh between these two openings.

However, vignetting is relatively present and there is also a cat’s eye effect that makes the image of a point light source slightly distorted. An onion-ring phenomenon is also present.

The minimum focusing distance of 39 cm is equivalent to that of the EF 24-70 mm f/2.8L USM II and if the lens does not achieve a macro ratio, its possibilities remain within the average of what this type of lens allows.

As for geometric deformations, they are present with a barrel distortion at 28 mm which tilts into a 70 mm pad, but remain very moderate. They are especially perfectly corrected by the EOS R if you activate the corrections on the fly in the device.

Finally, despite the weight of the lens, we appreciated the perfectly silent operation of the autofocus system. Unlike the RF 50 mm f/1.2L USM, which had an imbalance when operating the autofocus system, the lens operation is perfectly balanced. By using the electronic shutter mode of the EOS R, it is possible to photograph in an entirely silent way.

Optical quality

The notion of quilting is quite delicate to deal with. This is what we can assimilate to the “feeling of sharpness” or “precision” that we observe on an image. It can be very different from one lens to another, from one focal length to another and from one aperture to another. It can also vary between the centre and the edges of the image.

We tested the lens with an EOS R, the only compatible device at the moment. Its 24 x 36 mm sensor records 30.1 MPs, providing 6,720 x 4,480 px files. Each pixel, therefore, measures 5.36 µm on each side. The results were evaluated using the Imatest software.

Regardless of the focal length used, the RF 28-70mm f/2L USM has very nice dive curves. The resolution in the centre is high at all openings, slightly below f/2, but still very good. Above all, the lens delivers very consistent performance between the centre, edges and corners of the image. We will not hesitate to use it at full aperture at all focal lengths and even up to f/16 where the diffraction remains moderate.


It is difficult to conclude on this extraordinary lens. If we were to judge only its manufacturing quality and optical performance, it would receive the highest score, as it is a great feat to succeed in producing such a good lens from an optical point of view with a constant aperture at f/2. But lenses are used by photographers in the field, and here our judgment is more nuanced. The RF 28-70mm f/2L USM is very heavy and bulky, which goes against the philosophy of hybrid cameras and especially the quest of most photographers. Is the increase in brightness worth the lack of stabilisation and the additional space requirement? Of course, many photographers are convinced of this.

Last update on 2020-10-14 at 19:18 / Affiliate links / Images from Amazon Product Advertising API

Aether has been playing World of Warcraft since 2006. In his youth he raided 7 days a week, but now just plays with friends doing Mythic dungeons and Arena. He swaps his main more often than he should.
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