Introduction
Canon has upped the game compared to their DSLR lineup with pretty much every new lens they released for the EOS R system. They added an IS on the RF 24-70mm f/2.8, released an RF 28-70mm f/2 with a speed never seen before and made the RF 70-200mm f/2.8 shorter than any comparable lens in its class. And in the ultra-wide zoom segment? They are now offering the Canon RF 15-35mm f/2.8 USM L IS – a lens that is wider and adds an IS while still avoiding the bulb-like front element that we’ve seen in most other modern designs. Unsurprisingly, it’s also a pricey lens at 2300USD / 2500EUR. Please note, however, that this is just a little bit more expensive than the EF 16-35mm f/2.8 USM L III at the time of its release and you are getting something extra here. Still, hopefully, Canon is going to offer a more moderately priced f/4 variant for the rest of us in the near future.
The RF 15-35mm f/2.8 USM L IS is a big lens with similar dimensions and even a marginally increased weight compared to its EF “predecessor”. Unsurprisingly, it follows the usual RF design philosophy. It uses some kind of very high compound material for the body, combined with big rubberized focus- and zoom rings. At the front, there’s also the additional, customizable control ring for those who prefer to have an aperture, ISO or exposure control on the lens. Needless to say, the lens is also dust- and splash-proof. Fluorine coating on the front element helps to repel dust and water as well. However, a slight downside is the extending zoom mechanism. The inner lens tube extends by about a centimeter towards the WIDE end which is a little unusual. A very short, petal-shaped plastic lens hood is part of the package.
The AF is, once again, based on Canon’s Nano USM which offers both very fast as well as noiseless AF operations. Focus accuracy is very high at 15mm but it suffers a little beyond when stopped down a bit (residual spherical aberrations). To be fair – in real life, any inaccuracy will usually be hidden within the immense depth-of-field. Manual focusing works “by wire” but other than the lack of a focus distance scale, you won’t really notice much of a difference compared to a mechanically coupled focusing system. The IS has a claimed efficiency of up to 5 f-stops. Based on our real-life experience with the lens, we’d say that it’s 1-2 f-stops less than that though.
| Specifications | |
|---|---|
| Optical construction | 16 elements in 12 groups inc. 2x UD & 3x aspherical elements |
| Number of aperture blades | 9 (rounded) |
| min. focus distance | 0.28m (max. magnification ratio 1:4.76) |
| Dimensions | 88.5×126.8mm |
| Weight | 840g |
| Filter size | 82mm |
| Hood | petal-shaped (bayonet mount, supplied) |
| Other features | weather-sealing, image stabilizer (5 f-stops), additional control ring, fluorine coating |
Distortion
Image distortions tend to be a weak point with ultra-wide zoom lenses – especially in the mirrorless category. However, Canon stayed true to its tradition by correcting most of them. Of course, there are visible barrel distortions at the 15mm setting. But at ~2.8% they stay within the standards set by very good DSLR lenses. At 18mm the distortions have been reduced albeit you can spot a mustache-style sub-frequency in there. Beyond, the distortion switches to pincushion-style on a comparatively mild level.
If you prefer your images to be free of distortions, you can, of course, just rely on image auto-correction, which perfectly handles all this, as you can see below.
Vignetting
Some readers already “warned” us to prepare for very high RAW vignetting figures with this lens – and yes, at 15mm f/2.8 and a whopping 4.6EV (f-stops) they are even exceeding Zeiss levels and this is, I’m sorry to say, among the worst that we have seen here. That’s almost 2 f-stops more than on comparable DSLR lenses and surely a side-effect of the shorter distance between the rear element and the image sensor. Stopping down reduces the issue substantially but it remains easily visible at all settings at 15mm and 18mm. The light falloff decreases at the more you zoom out but it’s always very noticeable in the f/2.8 to f/4 range.
FWIW, 4.6EV vignetting looks like this:
Now that’s the RAW vignetting but image auto-correction comes to the rescue – at cost of increased sensor noise due to the signal boost. Surely also for this reason, Canon doesn’t eliminate all vignetting but just reduces it down to a more bearable level. Thus at the wide end, you will still experience a heavy light fall-off of more than 2EV at f/2.8.
MTF (resolution)
Coming back to a more pleasant aspect again – the resolution. At 15mm, it’s downright superb in the broader image center. Unsurprisingly the outer image field suffers a bit at f/2.8 but it remains very decent. You can spot some softness in the far corner pixels (beyond the coverage of the test spots) though. Stopping down lifts the borders/corners nicely. The borders are even entering excellent levels at f/5.6 and the corners are good to very good here. Beyond diffraction is limiting the quality albeit primarily in the image center until about f/11. Generally, f/16 and beyond should be avoided. The wide-open performance suffers a bit at 18mm f/2.8 in the borders/corners but the overall quality is actually slightly better at medium aperture settings. The same goes for 24mm. There’s a slight drop in quality at 35mm primarily at f/2.8. Even so, the outer image field remains good and is top-notch from f/5.6 again.
The field curvature is low at 15mm but increases at longer settings. The centering quality of the tested sample was good but not perfect.
Please note that the MTF results are not directly comparable across the different systems!
Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure of sharpness. If you want to know more about the MTF50 figures, you may check out the corresponding Imatest Explanations
Chromatic Aberrations (CAs)
Lateral CAs are very well controlled. They stay around the 1px mark at the image borders across the range. You may just spot this when doing pixel peeping but it’s really not an issue in real life.
Bokeh
We haven’t taken the lens through our usual bokeh torture ground. However, we did take a couple of snaps at large-aperture settings during our field session.The first image below was taken at 35mm f/2.8, the 2nd one at 18mm f/2.8. I think it’s safe to say that the out-of-focus blur is quite pleasing for an ultra-wide lens. There are some further shallow depth-of-field images in the sample image section.
Flare and Sun-Stars
Flare is always a hotly debated topic with ultra-wide lenses simply because they have to battle stray light more often than longer lenses. Generally, you can push ALL lenses beyond their limits – no SWC or ASC coating is ever perfect. It’s just a question of how bad it gets. Below is a worst-case scenario with the sun positioned at the image borders in a rather darkish environment. As you can see, there’s a blueish blob in the image corners. Glare is well controlled for a zoom lens.
The image was taken at f/13 and the “sun-stars” should be “quite” obvious here.
Sample Images
Canon wanted to have the "holy trinity" of fast zoom lenses out in the wild as soon as possible after the launch of the EOS R system. However, despite the rush, they didn't forget about making it right and that also applies to the Canon RF 15-35mm f/2.8 USM L IS. "Historically," Canon's ultra-wide lenses weren't exactly their strongest segment but this has changed at least in the last generation of their offerings. The RF 15-35mm has a few weak points but overall, it is, once again, one of the best ultra-wide lenses that we have tested so far. The resolution characteristic is generally very good, especially when stopped down but it's also decent at f/2.8 - and that's across the focal length range. Image distortions are also moderate for such a lens and unless you require perfection, you won't really require image auto-correction for this aspect. That can't be said about vignetting, though. The light falloff is rather excessive at the wide end. While some of this can be explained by the "natural" vignetting that is always present, it's a bit over the top, to be honest. Thus unless you are after a keyhole effect, better use image auto-correction here and even then you'll notice darker corners at f/2.8. Lateral CAs are well controlled and a non-issue in real life. The quality of the bokeh is good for such a lens. The lens is quite flare-resistant but certainly not fail-safe - no lens is.
The build quality is, of course, targeting professional use and it's on a correspondingly excellent level. The materials and assembly quality are top-notch. Weather-sealing is a natural feature at this price point anyway. Some may not like the extending zoom mechanism though, and it's also quite a brick, to be honest. The AF is extremely fast and noiseless. Just like on the RF 24-70mm f/2.8 USM L IS, Canon finally managed to incorporate an image stabilizer into the lens. Given its ultra-wide nature, this wasn't quite as urgently needed but users will certainly appreciate this in low-light situations - although we won't be on the 5 f-stops efficiency claimed by Canon here.
At this stage, you don't really have much of a choice when it comes to R-mount lenses in this class. However, if you are a professional photographer or pumped up financially, there'll be no need to look elsewhere anyway. Highly recommended!
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Optical Quality (30mp)
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Build Quality
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Price / Performance