Quote Originally Posted by Chan Tran View Post
There is no such pin when open the back of the camera. There is a bar that push the pin. This bar is pushed by a level. This level is mounted on the side of the mirror box but it can not be seen unless disassembled.
I'm saying that you should be able to see the plunger in the camera, pushing the pin on the lens, if you looking in through the gate in the film plane when the shutter is open. If the plunger is not pushing all the way out against the pin, you should be able to see it.