Canon EF 85 mm f/1.2L II USM
7. Coma and astigmatism
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We were a bit surprised by the coma correction. Dealing with this class of lens, sold at a very steep price, we expected that, at least on the APS-C sensor, we wouldn’t be able to notice any coma at all. That exactly situation has taken place in the case of a cheaper Canon EF 1.8/85 USM, a lens with a faultless coma correction. Instead, we were rather disappointed here – the coma is seen on the small sensor not only wide open but also after stopping down by one stop. The stopping down does lower the level of the aberration but it doesn’t eliminate it. Of course the situation is much worse on full frame. We didn’t expect a full coma correction by f/1.2 because it is really difficult. We thought, though, that on stopping down that aberration will be not burdensome and, unfortunately, it is still significant. Here we have the first slip-up.
Luckily, the tested lens can’t be faulted for astigmatism correction. The average difference between the vertical and horizontal MTF50 function values amounted to 3.6% which is a very good result.
