I've tested out these lenses and compared them to each other. I've shot the same subject at various apertures. The zooms I compared at 45mm. The 75mm was compared to the 45-85 zoom set at 75mm. This was not a full blown test but basically for testing my repaired 33-55 zoom. I alsowanted to find out what you miss in optical quality by going the zoom route (45-85) compared to the 645 75mm standard lens.
In short the two zooms are totally identical with regards to sharpness and resolution; I can't see any difference between them. I do suspect, however the differences are very subtle, that the 45-85 is slightly sharper wide open. I also suspect that its contrast is a tiny bit higher. It seems to me though that the 33-55 is a tiny bit sharper at F:16. The 33-55 has its peculiarities though. Primarily a higher distortion and the fact that its plane of focus is more a sphere. If these characteristics could be lived with, only the focal lenght range of the lenses and weight are deciding factors for choosing between them. The 75mm prime is slightly sharper at F:4.5 and F:8 than the 45-85 zoom. Mind you, the differences are so small that you have to go back and forth between the images of the same subject to spot the differences. At F11 they approach each other and at F:16 they are for all practical purposes identical. The standard lens has a slightly cooler color rendition than the zoom but again the diferences are so small than only going back and forth between the same subject is it possible to spot. The two zooms have totally identical color rendition. To conclude: the two zooms, and together with the 150-300/5.6 ED IF zoom, are superb lenses with similar optical quality. The difference in quality to the standard lens for the 645 system is so small that it cannot be detected unless by side by side comparisons of the same subject. P�l
