Canon EF 85 mm f/1.8 USM review - Vignetting

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Canon EF 85 mm f/1.8 USM

8 March 2011

Arkadiusz Olech

8. Vignetting

Let’s start from the small sensor of the Canon 20D. The photos of uniformly lit surface photographed by the tested lens attached to that camera are presented below.

As you see the vignetting at the maximum relative aperture is noticeable but not especially bothersome. Its value we assessed as 24% (-0.80 EV). On slight stopping down to f/2.0 we see this aberration decrease to 20% (-0.66 EV). Implementing f/2.8 aperture makes the problem disappear completely because then vignetting amounts to just 7% (-0.23 EV).

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If you attach the Canon EF 85 mm f/1.8 USM to any full frame camera its task will become much more difficult. The photos below show it rather well.

At the maximum relative aperture we deal with a significant level of brightness loss in the frame corners. According to our measurements it is 47% (-1.84 EV). When we use f/2.0 aperture the vignetting decreases to 41% (-1.53 EV) and on stopping down to f/2.8 it drops further to the value of 21% (-0.69 EV). The problem disappears completely by f/4.0 and f/5.6 where the level of this aberration we assess as 14% and 9% respectively.