Used with a 645z, the weather sealing and light weight make this an awesome performer in inclement weather. Fantastic contrast, sharpness and bokeh.

Exceptionally good lens. I test images based on the default raw processing settings of DXO Photolab, and this lens is in their database, so distortion and lateral color are automatically corrected. I tested this on a 645z.

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  Surgically sharp without being harsh

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  None

Spectacular lens. Extremely sharp on the Pentax 645Z, great contrast, and small footprint. Great grip. Little to no flare, even shooting directly into the sun. Only minor quibble is that there is some purple fringing against bright light. Fantastic value.

That is a wonderfully sharp prime lens! Shooting on my Pentax 645z is a dream for that innate medium formate look. I would nightly recommend this as a must have in your camera bag...

I just carefully examined the optical performance of three copies of the 55 D-FA lens on a 645Z body. By any traditional, fussy standard, all three copies were exceptionally fine lenses, in my tests being essentially perfect from corner to corner from f/5.6 on up.

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  Superb overall optical performance from 5.6

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  Not quite up to wide-open star capture work, hard to focus for wide open at infinity

This lens can uses in Pentax 645D, I think it is a good lens, but the only thing I think it is not good enough is the depth of focus. Any way, this is a good lens I think. I like it.

its perfect for the new 645z. the weight is awesome for the quality.

This is a really good lens. I was nervous about buying one because reviews are not unambiguously positive, and it's not spoken of much outside this forum. I'm glad I took the chance. I wanted something faster and lighter than my fantastic 45-85/4.5 SMC Pentax-A 645 zoom. This fits the bill.

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  Well built, reliable, sharp

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  A bit heavier than I'd like...

I gave 8 because of the sharpness decrease at corners when I focus at infinite (see below for detail). Other than that, this lens is really good. I would recommend this lens except those who frequently focus at infinite.

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  Sharpness at the center

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  Field curvature, CAs at the corner

This is the standard for the Pentax 645 D. It is sharp, has good contrast, and responds quickly to the auto focus. I have not noticed the soft corners that some reviewers have mentioned. The lens hood has a panel that can be removed to access filters. This is a nice feature.