Canon EF 28mm f/2.8 IS USM
Image Qualityshow all test shots
Note: the test shots for each of the image quality tests can be compared directly amongst all tested lenses. Within the test box click on "Choose lens to compare with..." to add a lens to the comparison. Then use your mouse to hover over the lens thumbnails. If all those test shots are a little too overwhelming consider clicking on "hide all test shots" above this paragraph.
Sharpness / Resolution
If you are buying a prime lens you expect it to be sharper than most zoom lenses. And the EF 28mm f/2.8 IS USM certainly is: compare the test shots below with the EF 24-70mm f/2.8L USM to see how well the EF 28mm f/2.8 IS USM performs. It outperforms the zoom lens both wide open and stopped down. Compare the Siemens star (3) and the pattern banners (4) to see the dramatic difference in detail resolution. The lens is much sharper than the EF 28mm f/1.8 USM, still a little sharper than the EF 24mm f/2.8 IS USM and similar in sharpness to the EF 24-105mm f/4L IS USM (compared at same apertures). Overall it's a sharp lens indeed from the image center right to the corners.
The EF 28mm f/2.8 IS USM shows only a small amount of barrel distortion which is nothing to really worry about. The lens's performance is very similar to the EF 28mm f/1.8 USM and it is much better than zoom lenses such as the EF 24-70mm f/2.8L USM or the EF 24-105mm f/4L IS USM who offer a similar (but not the same!) focal length.
Crop from top of image (downsized)
Crop from bottom of image (downsized)
Color Errors Transverse Chromatic Aberrations
The EF 28mm f/2.8 IS USM shows quite visible color fringes in focused parts of the image at high-contrast transitions. Note that this type of color fringe is worse towards the corners of the image and is not really visible in the center. It is best compared at f/8 where those other color fringes that are affected by aperture are less dominant. The lens's performance is similar to that of the EF 24mm f/2.8 IS USM but evidently better than that of the EF 24-105mm f/4L IS USM and the EF 24-70mm f/2.8L USM (at similar focal lengths).
Beauty of blurred image parts Bokeh and Axial CA
The EF 28mm f/2.8 IS USM uses 7 aperture blades to create a nicely round aperture shape. That's important to make background blur pleasing and even. At the transition between in-focus and out-of-focus image parts color fringes do occur with the EF 28mm f/2.8 IS USM but they are not too bad and they fade with higher f-stops.
Curvature of the focal plane Field Curvature
Fortunately the EF 28mm f/2.8 IS USM does not have any relevant curvature of the focal plane.
Corner Shadow Vignetting
When used with a fullframe camera wide open the EF 28mm f/2.8 IS USM shows a massive amount of corner shadow. Stopping down helps but it doesn't completely remove the shadow (part of which is just plain physics and cannot be avoided). In-camera vignetting correction or post processing can further help to get rid of it (in case you actually bother). Even with an APS-C camera you can still notice some corner shadow. The lens is much worse than the EF 28mm f/1.8 USM (compared at the same aperture). It is actually even worse used at f/2.8 than the other used at f/1.8 which is a stop and a third wider. Note however that many photographers are not bothered by corner shadow at all because of the particular look it has.