Just got out of the basement from running tests of my various optics against a USAF resolution test chart. It's raining like crazy here and the wind is of Wizard of Oz proportions, so I didn't feel bad about testing instead of going outside and shooting live subjects.
If I have time in the future, I may write up something more complete. Until then, my words and calculations will have to do.
To get an idea of what my optics and camera would do in my situation, and ignoring the fact that MTF measures contrast reproduction and USAF resolution test charts measure resolution - leading to vast differences in how results are to be interpreted, understood, applied... on a Canon 40D mounted to a sturdy tripod and letting the AF do it's thing, measuring line pairs per mm (same as saying lines per mm), at a target 114inches from the CMOS sensor plane...
...three numbers: Center ~ Middle ~ Edge of the frame...Canon EF 28mm f/2.8
f/2.8 82 65 52
f/4.0 82 65 58
f/5.6 82 65 65
Compared with other DSLR lenses I tested, this is a really nice result . The edges come up cleaner and sharper as the aperture is stopped down. This is a seemingly sharp little optic.