Canon EF 85mm f/1.8 USM - Review / Test Report - Analysis
Lens Reviews - Canon EOS (APS-C)

Distortion

As expected for a fix-focal lens the level of distortion is negligible:

The chart above has a real-world size of about 120x80cm. Possibly things may get a little worse with extreme close-ups.

Vignetting

Vignetting is very well controlled with the lens - at least on a 1.6x DSLR. Wide-open vignetting doesn't exceed ~0.7 f-stops here - it's probably quite a bit more on EOS 1D cameras. In critical scenes vignetting may be noticeable on APS-C DSLRs as well. However, the problem is basically non-existent from f/2.8 and up.

MTF (resolution & chromatic aberrations)

The lens performed OUTSTANDING in the lab and that's at ALL aperture settings (at least till f/8). The performance peaks at f/4 but even at f/1.8 the results are more than impressive. The lens was designed for full-frame cameras so the 8mp APS-C sized sensor takes only advantage of the sweet spot which certainly helps here.

The lateral chromatic aberrations (CA) don't exceed an average of 0.61 pixels at the image borders so they're quite low and usually no problem. However, in extreme light situations you can observe some purple fringing (see fountain shot in the samples section).

Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness. If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations




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