I've been using my B x J 11 x 14 for 30 years in the field. I recently bought a 12" Goertz Dagor--a fabulous lens with great coverage, but it has no shutter. It is tricky to add a shutter to these, because then lens has be be taken apart and re-milled. Does anyone know of a shutter that can be added to the FRONT of such a lens?