My enlarger lens a Schneider Componar-C 50mm f3.5 kept jamming around F4 so I decided to strip it down, it was a little dusty on the elements. Anyway these things have hinged 2 piece iris blades. after 2 hours of trying to get the damn thing back together I gave up and bought a replacement Componon-S f2.8 on fleabay (may as well have a bit of an upgrade while I'm at it). Tried again this morning and it went together in 15 mins, all working properly again :bonk: Why is it as soon as you sort a replacement you manage to fit it!!!