Zeiss white paper on MTF
Zeiss has posted How to Read MTF Curves, Dr. H.H. Nasse (of Zeiss). It goes into the details of how to interpret MTF. It is well worth reading, keeping in mind that MTF is only one measure of lens design, with everything a tradeoff. See also How to Read MTF Curves II.
Read the very last page first, then read the last few pages, which sum up nicely how dubious MTF can be when comparing different brands, and why field shots with real images will always be a better way to assess lens performance as an integrated whole. That is why I spent so much time in Guide to Zeiss making many examples that show how the lenses perform for making real images. After you’ve read the last several pages, then go to the beginning.
