Look Bertram2,
MTF is a standard concept in scientific literature. Frequency analysis was a main stream tool in Control theory at the end of the forties. I remember the book by Truxal on Automatic control synthesis I read as a student in 1965 (Amazon still has it), which is entirely based on frequency analysis.
Similarly in Optics. The literature is immense in both disciplines. For Optics a classical reference is:
Principles of Optics, by Max Born and Emil Wolf, Cambridge, first edition 1959.
After my degree I taught frequency analysis for decades. Now all this is rather outdated (in Control), but it holds good anyway, and has remained main stream in Optics.
You and me and all other human beings can escape anything but Math and its Theorems.
So if you have good eyes for photos, you will be able to see what MTF says, and if you know MTF you have a very precise idea of what to expect, even before buying a lens, so to make informed decisions.
Cheers
Paul