The OLPF extends the physical distance between the rear of the lens and the sensor, by maybe 0.6 mm?
The back of the 25mm Baltar (small type in BNC) should clear the optical image plane by maybe 15mm+ (?) so if the OLPF is far enough back and the mount has clear space I don't see why it would not work. Some OCT-19 lenses are in non-reflex BNC type mounts, you might shim a OCT-19 mount out about half a mm and use it with the BNC lenses. It there is an obstruction you just need to put the mount on a lathe and cut the hole deeper.
OCT-19 seems to have started as BNC, but at some point, maybe because the rackover gibs were warn down, they rounded off the f2f to a metric value about half a mm shorter. Some RUSSIAN lenses are BNC, and so don't focus right on a Konvas-2M unless you take some metal off the mount ring. They also changed the round pin to a square one, you can slot one tab on your lenses to work with the square pin, since the lens can rotate in four directions without the reflex miror. The OD is about the same, but Mitchell made everything a close fit, so you may need to open the mount hole a few 1/10000" to get the lens to slide in. I have seen Russian sellers with BNC/NC cameras, and with what look like NC movements in their bodies. They may have gotten the Mitchells as part of WWII "lend lease" or from Poland/Germany etc.
I think original Mitchell mounted BNC lenses had an adjustable focus mark, so you can reset the flange-to-focal on them, they needed the mark ring to turn because of wear to the rackover gibbs (sp?). We have one older Russian 28mm that seems to have been made for both non-reflex and reflex use with BNC focus, I adjusted it for Konvas-2M use, it had an adjustable focus mark, but being made of brass and AL I was unable to turn it since the metal was a bit corroded, but is was like a copy sort of a Mitchell type BNC mount. Seems quite sharp made in the 1960's I was told from Zeiss glass perhaps.
To adjust the mark you take the lens out of the mount and turn the top ring on the mount part (on the camera half fo the mount not the lens part) until the mark ring is lose, then you can screw the lens back in, focus on something, run a tape, then rotate the mark to match the tape, unscrew the lens (the whole front part with the lens in it, not just the lens) and tighten the top ring on the mount that locks the focus mark.
The wide angle lenses like 24mm Cooke Series I, and small 25mm Baltar may be a bit dark in the corners because the are at a steep angle to the sensor (off the sensors microlens peak), but later retrofocus lenses, and longer fl should work.
Originally Posted by Björn Benckert
