19 inch Artar"lever"

[Dave Willison]

What is the purpose of the small brass "lever" on a Goerz Red Dot Artar (19")? Moving the lever reveals a slot in the lens housing. Is this slot for filters or some other application for using the lens as a process lens

[james mickelson]

It's for filters. James

[Rob Tucher]

Or for Waterhouse stops that are like f/stops but are calibrated in a way that makes graphics exposure/magnification calculations possible. Process lenses don't generally need filters much indoors.