old style canon 1.8.

[Deleted]

i have an FTb, and an old style canon 1.8.
maybe someone can tell me what the small lever on the inside of the mounting ring is for?
it has two positions a red L and a white dot.?
thanks

[casualcollector]

It's a stop down lock for using the lens on bellows, uncoupled extension tubes, or reversed for close-ups. Move the stop down lever to the right, hold it in position, move the toggle to lock the lever in place.