From Salviano Junior
After reading Carl and Mike's Pentax 35mm DA Macro review on Photo.net, and as a Pentax K200D/35mm DA Macro owner, I invited people to participate in a test with the purpose of investigating the correlations between MTF numbers/graphs and images. We have now had a variety of participants, and I want to publish the results here.
My conclusion after all is said and done:
MTF numbers are an objective measure of optical quality. The bigger the number, the better the optical quality of the glass. But is hard—if not impossible—to do exact measures of the impact of this optical quality in "real" photos, even when using an accurate technique. (But not scientific—a photographer don't need to be a scientist).
In this experiment, the relative difference in MTF numbers of 43% (border) and 38% (center) was easily identifiable. But the differences of 3%, 10%, or even 24% didn't give a solid argument—and was not translated, in practical terms—to theoretical optical superiority.
Probably, it is not a good idea to take the MTF numbers so seriously. It's a measure of optical quality but not a guarantee of superior visual results (that is to say...optical results). There are too many unmeasurable factors involved, beyond the optical quality of the glass to control, and each one of them affects in some degree the visual result.
And if one experienced photographer tests a lens and gives to it his highest rating, and another experienced lens reviewer tests the same lens, but doesn't demonstrate such enthusiasm—?
Well, I don't see any contradiction. It's a matter of preferences, subjective opinions. A matter of distinctive point of views, but not different languages (regarding optical quality), therefore both are valid.
My subjective opinion is: I agree with Mike Johnston and Carl Weese when they rated the Pentax 35mm DA 35mm Macro Limited as "An Optical Paragon."
And thanks to Klaus Schroiff for providing the MTF numbers—in my opinion, these numbers don't contradict the Mike/Carl "thesis"—so no disagreement there either.
Want a second opinion? Take the test yourself. Follow this URL:
I provided the untouched RAW-DNG files under Creative Commons Attribution 2.5 Brasil License.
Rio de Janeiro