In spite of trying to pare down my camera collection (see my classified ads), I recently bought a user 12x20 camera to do some studio stuff. I'm not up to taking this beast out in the field!
Today I received a 19" Apo Artar lens for the beast. There is the aperture adjustment ring of course, but there is also something that looks like it is for some sort of waterhouse stops. It opens up the side of the lens. Talk about light leaks! Better make sure that it's closed before making an exposure.
Question: What's it for? I don't know why you'd use waterhouse stops when you have the aperture ring/blades built in. Forgive my ignorance. Can anyone shed some light?