Canon FTb and 50 1.8 BL: mirror stuck

I just took delivery of a Canon FTb body and 50 1.8 BL lens from KEH.

The mirror gets stuck in the up position after I fire the shutter, and doesn't move back to the down position until I loosen the breech lock on the lens 1/8 of a turn. This problem doesn't happen with my FD 35 2.8 (non-BL).

If I mount the problematic 50 1.8 on my Canon T50, the mirror does not exhibit the same issue.

The mirror bumper looks recently replaced and is not sticky. The mirror rebounds freely with no lens mounted and the MLU lever is set to the the white dot ("normal operation"). I'm guessing the mirror is getting hung up on the rear of the lens, though I doubt it is the rear element as it still hangs even if I zoom the element all the way in.

Is there a compatibility issue with the FTb and BL lenses?

No, it is a typical combo.

At the moment I have no idea for that strange relation between the mirror movement and the mount.

You might use a cable release at the B-setting and lock the release.
With back door open you then could se the actual position of the mirror.
Though I do not see great chance that such would make you wiser, but still is worth a try.

Notify KEH, they will pay for shipping to replace it.

The poster did not indicate where he is located. Outside the US return to KEH would be troublesome.

This shouldn't be happening but it sounds like the mirror is just touching the back of the lens when in the up position. If the lens is focused at infinity, this is the worst case. If you focus the lens at the closest focusing distance does the mirror still stick in the up position? I have a Pentax spottie that will hold the mirror up when focused at infinity.

The fact that loosening the breech lock allows the mirror to return tells me there is an interference problem.

Fred Aspen said:

This shouldn't be happening but it sounds like the mirror is just touching the back of the lens when in the up position. If the lens is focused at infinity, this is the worst case. If you focus the lens at the closest focusing distance does the mirror still stick in the up position? I have a Pentax spottie that will hold the mirror up when focused at infinity.

The fact that loosening the breech lock allows the mirror to return tells me there is an interference problem.

Click to expand...

It doesn't matter what distance I focus at. The mirror hangs on the 50 1.8.

I tested with a 135 3.5 BL lens and did not have any issues with the mirror getting stuck.

I'm going to RMA the lens iwth KEH.