Sorry if this belongs in a different thread. At work, Ive encountered a mysterious problem: We have an 85 mm/1.2 EF lens mounted on a Letus Elite w/ the B4 mount. When mounted on the Letus in MF mode, the lens does not focus at all - the ring just spins around.

However, the same lens when mounted on the 5d Mark II works just fine. Furthermore, our other EF lenses (24,35,50,) seem work fine on the Letus.

If anything I'm guessing the problem's the lens, so sorry if this is the wrong forum, but why would the manual focus work on one camera but not on the letus? I'm at a loss.

Thanks in advance,

David

My wild guess is that this particular Canon lens is an autofocus lens and that manual focus slaves the lens focus servo motor to the movement of the ring as with many videocameras.

Take away the power and nothing will happen when you move the ring.

The other EF lenses may have a manual focus function that is purely mechanical, clutched in when you select MF and not reliant on power for manual focus.

Thank you, Bob, that turned out to be the case.

It's a beautiful lens, a shame that it seemingly can't be mounted on a 35 adapter for video like other EF lenses.