It's not a membrane or a diaphragm. It's just a 3 x 102 mm strip of velvet
felt, just like the light trap in sheet film holders. It's glued in a slot
sround the lens hole in the camera body. If it looks like it moves, it's
just the fibers bowing when the lens tube moves.
The ring Prochnow talks about, that "looks different according each
calculation" could be the lens tube. The velvet felt is just a light trap,
and can't do anything to improve the results other than avoiding light
leaks.
I got a new lens tube in one of my Rolleis I sent for repair. Don't know why
it was replaced (the old one looked good in my eyes), but the repairman
didn't charge me anything extra for that.
/Patric
From: Carlos Manuel Freaza <cmfreaza@xxxxxxxxxxxx>
Yes Richard, I have seen again the Rolleicord IV and really it has a membrane or diaphragm that appears when you put the focus mechanism at the minimum focusing distance, it has a reddish color and it's very different regarding the system for the 2.8C, while the 2.8C is similar to your 2.8E, (it moves following the lens movement as Todd explained), the Rolleicord IV membrane or diaphragm(there are no "bellows" here) is invisible till you advance the lens to the minimum focusing distance (0.80m), that was the reason I did not see it before. As Prochnow wrote, the diaphragm, (or short "bellows" or membrane or whatever) looks different according each "calculation". The Rollei TLR cameras anti-reflection system are very effective according my experience; of course, as you wrote, it is not perfect if you shoot into the sun, but for this case it sometimes helps to obtain a bit of flare control enough for some detail in the photo. Perhaps that issue about the roller reflection seen in some cameras has something to do with problems for this "diaphragm".-
All the best Carlos
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