Sharpness at 135mm

Our sharpness tests are carried out by photographing a real-world subject rather than a test chart. The Canon RF 70-200mm F4L IS USM was attached to a Canon EOS R6 camera, which in turn was mounted on a sturdy tripod. Self-timer mode was activated to steady the camera completely. Any slight tonal changes you may see across the crops are a result of slight changes in natural light during the shooting session.

The full frame at 135mm

At both the centre and the edges of the image, sharpness is excellent even at the maximum aperture of f/4. It maintains that level of sharpness until f/16, where it remains excellent but is ever-so-slightly softer due to diffraction. It gets softer again at f/22, with the worse results seen at f/32.

Aperture	Centre Crop	Edge Crop
f/4
f/5.6
f/8
f/11
f/16
f/22
f/32