Quote Originally Posted by Jos Segers View Post
Interesting because I use the lens very often. I was lucky to buy an almost new 67II, 165mm and 75mm as a set on the second hand market in the Netherlands for an exceptional low price. All items in new condition.
I am very impressed by the performance of the 75mm but would hesitate to use f4. To my understanding (Pentax 6x7) medium format lenses in general show optimal performance from f8 to f11? Is this lens in your opinion an exception? Are there any test reports available?

Jos.

The AL in this lens will prove its worth when you are shooting at minimum aperture of f22; in a non-corrected lens, diffraction will introduce softness into the image caused by light bending past then refocusing onto the common point. In all lenses, blue and green wavelengths can be brought to a common point fairly easily, but not red. With AL elements, one or more concentrate all three wavelengths to the one point, resulting in much improved colour and definition. This is why you should not shoot at f22 or f32 with a 55 or 45mm lens! Most of the SMC Pentax (modern) lenses are well corrected for their purpose; the 75mm AL must obviously have been Pentax's Eureka moment in lens design, much more so than its 75mm shift lens.

I would be interested in seeing MTF charts of this and other lens characteristics by Pentax, but they are very scant in terms of web availability. Only hobbyists seem to have taken any effort to test them. The best evidence of performance is to speak to people who use the lens.