Pentax smc FA 77 mm f/1.8 Limited
7. Coma and astigmatism
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The frame edges near the maximum aperture were not the best so we were curious whether the coma had a hand in that result. Looking at the crops below it can be clearly seen that it did. Its influence on the deformation of the circular diode is perhaps not very strong but it is certainly visible and it keeps the same, perceptible level even on stopping down by one stop. The Pentax visibly gives in to a Zeiss 1.4/85 which is faster so more difficult to correct. The lens also comes out poorly when compared to a Nikkor 1.8/85, which performance in this category is splendid or a Canon 1.8/85 – both of them corrected the coma better.
The competitors from Canon and Nikon corrected astigmatism very well too – in their case this aberration remained at the level of 5-6%. Luckily here the Pentax doesn’t stand out from its rivals and reaches practically the same result of 5%.
