I tried before manual focussing with 50mm EF F1.2 but since id=s focussing is done by the wire never manage to get the focussing achieved with the T90 and an FD 50mm F1.2 . Can any body tried an FD lens with the appropriate split screen on the 1D MK 3 + 4 which I know can take a split image focussing screen? I tried manual focussing with 4/3s and Sony A7 which is OK when the lens is closed down to F5.6 . Thanks . Chris at 68 yrs old still hoping for that elusive shot .