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Lens review

Pentax smc DA 70 mm f/2.4 Limited

20 November 2009
Szymon Starczewski

7. Coma and astigmatism


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The influence of the coma on a circular diode picture in the frame corner is noticeable but the problem is not huge and, luckily, it becomes marginalized on stopping down. You can observe it very well in the pictures below.

Pentax smc DA 70 mm f/2.4 Limited - Coma and astigmatism

A bit more problems you can have with astigmatism and perhaps it is the main culprit for a weaker frame edge performance at the maximum relative aperture. The average difference between horizontal and vertical MTF50 function values amounted to 10% which is considered to be a medium result.