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Forum: Pentax Medium Format 11-13-2018, 11:43 AM  
Grand Lens Test 13: REJECTED 645 DA 28-45mm ED AW SR—Lens damaged and returned.
Posted By kaseki
Replies: 18
Views: 2,772
I agree. If the price only incorporates the depreciation of having been pre-owned, then it has to be essentially perfect otherwise. And in any case, even a lower priced example with significant cosmetic blemishes fails the photographer if it fails its optical design intent.
Forum: Pentax Medium Format 11-13-2018, 07:58 AM  
Grand Lens Test 13: REJECTED 645 DA 28-45mm ED AW SR—Lens damaged and returned.
Posted By kaseki
Replies: 18
Views: 2,772
I don't know what is going on either, but here is a suggestion for a tedious experiment.

Hand focus at some distance, maybe half way from porch to lamp post. Do not change focus. Do not change aperture. Using a resolution target or similar fine structure subject, take photos at different distances, both along the optical axis and half way to the edge of the field. Repeat for a much different lighting condition.

Evaluate the images for whether the depth of field that you see agrees with theoretical values. Evaluate the images for whether the depth of field is different on-axis versus off-axis. Evaluate when the sun is shining on the target versus when the target is shaded. It looks to me in your exhibit above that dimmer objects are less resolved. I'm not sure how that can happen in physical optics when way above the quantum limit, but maybe an internal camera algorithm is meddling. For example, it could take less bright pixel data and smear it a bit to ensure no noise in any of the computed color channels. However, why wouldn't that be seen using other lenses?
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