Canon RF 100-500mm F4.5-7.1 L IS USM

Testers found it very sharp through the range: near prime quality at 100-200mm, a slight drop by 350mm, and some softening at 500mm because f/7.1 is already diffraction-limited on high-resolution sensors. Corners fall off only slightly. Lateral CA is very low (about 1 pixel), distortion runs from none at 100mm to mild pincushion at 500mm, and vignetting wide open is mild. Bokeh is smooth at the shorter end but can turn harsh beyond 300mm in busy scenes.

Autofocus and IS are excellent on the EOS R5 and R6, with very high hit rates on birds and pets. Testers using the original EOS R found AF sluggish and IS less effective at long focal lengths before firmware updates. Build quality is rated superb and fully sealed, though reviewers would prefer a non-extending zoom because of dust. The criticisms are the slow f/7.1 long end (f/6.3 by 400mm), the price, and extenders that only work from 300mm.

A long-term owner who has used it for nearly five years, for about 90% of his photography, calls it the most versatile telephoto he has owned. He reports that the weather sealing has survived -35°C in Greenland and soaking rain, and he praises its corner-to-corner sharpness, its fast and silent focus with eye-detection AF, and the 0.9m close focus.

His gripes are a tripod-collar lock that works loose, a zoom ring that still feels loose even at its tightest tension setting, and a control ring placed so close to the mount that he never uses it. He considers the price high but justified by how long the lens lasts.