Canon RF 100-400mm F5.6-8 IS USM

Testers found the centre sharp throughout the range, with the most even performance around 200mm. The outer frame is weaker: corners are slightly soft at 100mm f/5.6 but recover by f/8, and borders and corners drop off at 300mm and 400mm. Sharpness also falls when close focusing at 400mm. Lateral CA rises from about 200mm to roughly 2 pixels at the 400mm borders, and mild pincushion distortion and moderate vignetting are easy to correct.

Bokeh is the main optical weakness: highlights take on outlined, bubble-like edges, and the transition zone can look smeary and busy. Autofocus is fast and quiet, and IS is effective, though not every tester reached the full rated gain. The engineered-plastic barrel on a metal mount feels solid for the price, but there is no weather sealing and no hood in the box. Reviewers rate the value very highly.

Owners like how light it is. They describe carrying it all day on an R5 or R6 without strain, and two who moved from the EF 100-400mm II say they see little difference in image quality and prefer the lower weight. They report quick, accurate focus for motorsport and wildlife, and good results for whale watching and occasional close-ups.

The common complaints are the lack of weather sealing, the hood being an extra purchase (one owner's third-party hood blocks the lens cap), and weak low-light performance. One owner also says it is not as sharp as L-series lenses, while still calling it a good purchase.