Question about Linhof Master GTL Back

[Bob Mann]

I have a Master GTL with a 5x7 back. The back has a bail arm.

My question is about the "L" shaped bracket at the top of the bail back. It slides to the left when a film holder is inserted and seems to be there for a reason. I just don't see what it is doing, or should be doing when I insert a film holder. I have attached three photos with an arrow pointed to the bracket. On the bracket's left side is a small rod that projects to the right and hits the leading edge of a film holder when it is inserted. The whole "L" bracket slides to the left when a holder is in the camera. The ground glass frame has a channel for the rod so it must be a factory installed "feature" - not added afterward.

Any ideas/insight would be appreciated -

[Bob Salomon]

That is the tripping mechanism for the Prontor Professional and the Prestor shutters. Sinar and Wista have similar features. When the holder is slid in when using the Auto Back cable it closes the shutter and sets the aperture at the selected taking aperture. If you don't have an auto shutter it does nothing.

[Bob Mann]

Thanks - Bob