To follow up on David Goldfarb's recommendation of press shutter, used Copal Press #1 shutters from the Polaroid MP-4 -- the ones marked Polaroid MP-4 on the front, accept no substitutes -- are about the best value going among press shutters. The Copal MP-4 shutter has the usual Copal #1 "open shutter" lever, so is easy to use. And since it has no diaphragm its useless for anything but front mounting lenses, so commands low prices. It is the reason I hang my Luminars (and many other lenses too) in front of a #1 instead of a #0.