• The yellow squares in the graphics are showing the original aperture/right answer.

• The red arrows in the thumbnails are showing the position of each cropped area, associated to the original f/number and again,  associated with the graphic statistics.

For this experiment, I used brand new camera and lens acquired from legitimate, authorized and well reputed suppliers. The equipment seems not to be defective,  so I can't list any problem with it. Same to the lighting set-up, tripod, cable release and whatever.

I taken seven shots in sequence with different apertures, but same EV. I processed all files with similar settings - including sharpening - as I said before - the only difference was regarding the fine-tuning Smart-Sharpen/Lens blur. It's important to remember that all RAW files needs to be processed before presentation.

Important - added on 30-aug: To the 2nd round I used O (zero) value of sharpening for RAW conversion and when pp editing an equal amount of sharpening for all photos)

The photo taken with f/22 was discarded for boht rounds - because of the average low quality, when compared with the others. It is confirmed with a MTF number of 43% less when compared to f/8. But...

Notwithstanding the carefully technique to shot the photos, it was very difficult to find plenty valid correlation betwen the most of the MTF numbers and photos not taken in a laboratory environment - at least in the case of this specific test. See the results above to confirm that. Only two of six apertures are corrected identified, and the large amount of errors are much more relevant.

Ditto, the

Published also as a post on The Online Photographer (thanks to Mike Johnston)    

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.

I provided the untouched RAW-DNG files under Creative Commons Attribution 2.5 Brasil License.

Salviano Junior - Rio de Janeiro - Brasil