I have recently bought a secondhand Rodenstock 360mm lens (for my De Vere 10" x 8") but it came minus the retaining ring (which I was aware of). The Copal opening is a No. 3, can anyone provide a supplier who may stock or at least can get hold of retaining rings?
well, in the meantime, the thread is a common filter ring diameter, 62mm if memory serves me. So when you recover from finding out how much a retaining ring costs, find a 67-62 stepdown ring, file two slots in it and go shooting, just remember how much money you saved, and how much film you can buy with that money.
I have 3 different copal 3's with 3 different size rings so be careful. Standards went out the window with these. Safest way to not be disappointed would be to contact Mr. Salomon and order the correct one.