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Pentax 25mm f/4

Overview of Pentax SMC DA 645 25mm f/4 AL (IF) SDM AW

The Pentax SMC DA 645 25mm f/4 AL (IF) SDM AW is the widest lens in the Pentax 645 lineup, equivalent to a 21mm lens on a full frame DSLR (long frame dimension).

The rear filter slot accepts 40.5mm filters. The lens ships with a 40.5mm clear filter, and a 40.5mm polarizer filter.

The Pentax 25/4 is a good lens, but one that leaves the sensor underserved, as the Sony A7R + Zeiss 21/2.8 Distagon comparison shows, as do the various aperture series that explore its performance. Stop down to f/8 at the least, with f/11 generally needed for acceptable results to the edges and corners.

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