Have a look at Christian Buil's evaluation of canon lenses:
http://www.astrosurf.com/buil/50mm/test_us.htm
I modified older mechanical Canon F1.4 FD to fit EOS for wide fields, and I have to close it down to F3.5 or more. Then it is pin-point sharp, even at corners (of my 400d - full frame sensor, being larger, may show more coma).
http://www.iceinspace.com.au/forum/s...ad.php?t=39293
The whole job cost me <~100$.