It was my understanding that these two shutters were effectively interchangeable, but it seems they aren't.
The cells from my barrel-mount 14" Repro-Claron are a perfect fit in the Compound III from my 300mm/500mm Schneider convertible. I tried them in two different Copal 3S shutters, and in each case they would screw in about two full turns, then bind. One of the 3S shutters is the older version with a non-linear stop progression, the other is the newer type with a constant spacing between stops.
I also tried moving the cells that live in the Copal 3S shutters. While those cells can be swapped between the two shutters with no difficulty, they won't screw in to the Compound more than a couple of turns before binding.
Compur 3 and Copal 3 are the same. Copal 3S is smaller and Compound III is different from that.
Just compared the Compound III and Copal 3S I have. It's the thread pitch. The Graphic Kowa 240/9 (Copal 3S) front cell will screw into the barrel of the Compound III just slightly, but quickly binds.
Thanks for confirming this Karl. I recall reading somewhere on the Interwebs that the shutter threadings were identical, but apparently not. They're oh-so-close, though
If you buy a Schneider lens in first generation Copal before they delineated 3 vss 3S they'll interchange. 210mm f4.5 Xenar (not the later 6.1 in Copal 1) and 300-500 Symmar both came in that early Copal right after the last Compounds were used. In that case they'll interchange and the barrel spacing will be correct.
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