Canon RF 10-20mm F4 L IS STM

Testers found the centre outstanding from f/4 at every focal length, with very good borders. The extreme corners at 10mm are only good, and the lens is stronger at 14mm and 20mm than at its widest setting. Diffraction starts to bite from f/11, so f/4 to f/8 is the working range. Lateral colour is low.

Uncorrected raw files show extreme barrel distortion and near-black corners at 10mm, so profile correction should stay on; with it, distortion is negligible and vignetting is moderate. Flare is mixed: careful framing keeps it minimal, but some sun positions produce obvious colour artefacts. Sunstars are attractive when stopped down. The STM autofocus is fast, smooth and silent, the IS works well for handheld video, and the sealed build is rated excellent. The main complaints are the price, filter use limited to rear gels, and the missing focus distance window.

Owners posting their first results say they are loving it so far. One owner compared it with the RF 14-35mm f/4 at the same focal lengths on buildings and found the 10-20mm drew walls less angled and more natural.

The practical concern raised in owner discussion is protecting the exposed, bulbous front element, since there is no thread for a clear or UV filter. Owner feedback on this lens is still thin, so treat these impressions as early.