Conclusion

The new RF 100-300mm F2.8L IS USM telephoto zoom represents the pinnacle of Canon's current lens technologies, although its sky-high price and sheer heft undoubtedly make it a niche proposition.

Taking the popular EF 300MM F/2.8L IS II USM prime lens as their starting point, Canon have daringly converted it into a much more versatile 3x telephoto zoom for the RF mirrorless mount, and have done so with no concessions made to either image quality or size.

This lens really does deliver bitingly sharp images throughout the zoom range, across the image frame, and through the aperture range.

Being able to shoot wide-open at F2.8 over the complete zoom range gives it a real edge when comparing it to the comparable shorter-reach RF 70-200mm f/2.8L IS USM or the slower RF 100-500mm f/4.5-7.1L IS USM zoom lenses.

This is made even better when you realise that the RF 100-300mm is fully compatible with the RF 1.4x and 2x tele-converters - suddenly you also have a 140-420mm F4 and 200-600mm F5.6 zoom lens at your disposal, with very little noticeable image degradation in real-world use.

You can comfortably use this lens handheld, but only really for short periods of time due to its 2.6kg weight. Holding it by the padded tripod foot and using the supplied shoulder strap works effectively, although using it on a monopod makes more sense.

The Canon RF 100-300mm F2.8L IS USM lens offered incredibly fast and virtually silent auto-focusing on the EOS R5 camera body that we tested it with, with the camera's AI subject detection and stellar AF system working in tandem with the lens' twin Nano USM motors to produce a very high percentage of keepers.

There are a few caveats even with this £11,499 / €11,999 / $9,499 lens to be aware of. The zoom mechanism is quite noisy, the 112mm front filter system is both rare and very expensive, the focus hold buttons are difficult to reach, and the tripod mount is both non-removable and non-Arca Swiss.

By far the biggest deterrent to ownership of this lens is that eye-watering price-tag - even if you add both extenders to further increase the zoom range and versatility, the RF 100-300mm is still really only a lens for the professional wildlife and sports photographer. The smaller and much cheaper RF 70-200mm f/2.8 and RF 100-500mm lenses make a lot more sense for enthusiasts.

If you can justify the cost, though, the RF 100-300mm F2.8L IS USM is undoubtedly the best telephoto zoom lens for Canon's full-frame mirrorless camera range, and one that we really don't want to send back...

Ratings (out of 5)
Design	4.5
Features	5
Ease-of-use	4.5
Image quality	5
Value for money	4