Specifications

Vignetting

On an APS-C DSLR the full frame EF 20mm f/2.8 USM enjoys a sweet spot advantage but the usually positive effect isn't all that pronounced regarding vignetting which is rather high at 1.28EV at f/2.8. From f/4 and up the issue is already very well under control and no problem under field conditions.

MTF (resolution)

The resolution figures in the lab were something of a mixed bag. The center performance is exceptionally high straight from the max. aperture. At f/4 it is even among the highest tested to date. Unfortunately the borders can't quite follow but the quality is still good to very good here. The extreme borders (data usually only obtained for dedicated APS-C lenses) show a rather pronounced fall off at f/2.8 which recovers by f/4. At f/8 even the extreme borders are in very good territory.

The lens exhibited a rather pronounced field curvature and a slight degree of residual aberrations (focus shift when stopping down) so you need to make sure that the depth-of-field is sufficient for your scene.

Below is a simplified summary of the formal MTF findings. The chart shows in line widths per picture height (LW/PH) which can be taken as a measure for sharpness. If you want to know more about it you may check out the corresponding Imatest Explanations.

Please note the new scale of [650,2150] which will be used for all EOS tests from now on.

Chromatic Aberrations (CAs)

CAs (visible as color shadows at harsh contrast transitions) reach an average CA pixel width well below the 1 pixel barrier which is very good for a lens in this focal length class.