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!