MTF

[mark_goldsmith1]

I hope I can ask this question right.

 

Does a MTF figure of 2113 (for nikkor 28-70/2.8 taken at 28mm) necessarily

sharper than a figure of 2028 (for a nikkor 17-55/2.8 taken at 24mm), both at

the center.

 

Please note that the spirit of this question is not to compare the lenses, I

just want to know how much we can rely on this measurements. Thanks

[tommyinca]

You may be referring to other types of resolution measurement system. MTF results are normally listed as a floating point number between 1 to 0 associated with a line pairs per milmeter (e.g.: 40lp/mm) parameters. In chart form, the x-axis is typically distant to the center of lens.

[alex_lofquist]

MTF also means Mean Time to Failure.

[andy a.]

I'm guessing those numbers are line pairs per picture height, and the two are very close to each other, maybe even within the standard of error for that type of test.

[yeux tortu]

Yes, it is sharper, the measurement is independent of focal length.

[yeux tortu]

Read Mr Atkins article;

 

http://www.bobatkins.com/photography/technical/mtf/mtf1.html

[yeux tortu]

Looks like photozone MTF ratings.

 

I think they do a good job but they test a limited amount of samples. Directionally the results are right, but degree of difference is probably not as precise as the numbers would seem to indicate. Their quantitative rating of the Nikkor 85 1.4 and 70-200 2.8 is probably inconsistent with my field impressions (I think they are sharper than measured). But perhaps the mythical status of these lenses clouds my perception of results.Or maybe I have better samples than the loaners which they tested.