A second lens that I tested during a big weather event. It was raining like crazy around here and the wind was of Hellenic proportions. I didn't feel bad about testing instead of going outside and shooting live subjects.
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...
EF 50mm f/1.8 II
f/1.8 46 52 52
f/2.8 52 52 58
f/4.0 73 73 65
f/5.6 73 73 65
I see that the resolution is fairly flat across the field. By f/4.0 this seems like a sharp little lens. The performance at wider apertures might actually be better than whats recorded here, but for that kind of test I would use Live View and 10X magnification to carefully focus.
For $70USD new, this is really a nice lens!