Hi, I am having some problems with my 40D and 50mm 1.4. It seems that when together they don't seem to work properly, the focus seems inconsistent. When I use other lenses on the 40D they are fine, my 10-20 is super sharp and spot on with the focus, same as the 24-105 and when I put the 50mm on my 400D it is also sharp and in focus, even at 1.4
My question is, what technology is used for the camera to talk to the lens? and could the my 40D with my 50mm just not want to talk to each other, even though they are fine with other cameras/lenses?
I will do some tests to show you the issues, but just wanted to check this first.

