Originally posted by seppstefano Isn't lp/mm a measure of resolution rather than of contrast anyway, or am I missing something?
Line pairs per millimeter, as a spatial frequency,
is one of the coordinates for measurement, the other being contrast.
So a good lens may deliver a contrast of 50%
at a spatial frequency of 40 lp/mm
(at a certain part of the image field,
for a certain color of light,
when focused at a certain distance,
in a certain orientation, . . . It's complicated!)
Originally posted by seppstefano Best of all it would be nice to find MTF test for K and M mount lenses.
I included Pentax' charts in my December 19, 2011 review of the M100/2.8:
SMC Pentax-M 100mm F2.8 Reviews - M Prime Lenses - Pentax Lens Reviews & Lens Database
Photozone did a test on the K135/2.5:
Pentax SMC-K 135mm f/2.5 - Review / Lab Test Report - Analysis
You may find some others scattered in cyberspace.