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Switar 10mm 1.6 loose C-mount thread


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Hi all,

somehow since I last used it a few months back the rear thread on my 10mm (most used lens) has become loose. It just spins round freely so although it can be threaded onto the turret of the Bolex it's not useable. I've taken the back lock ring off and made sure everything is lined up but it won't screw down deep enough to lock the camera mounting thread in position. I hope that makes sense. 

Has anyone come across this? 

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I have seen this on a bunch of my lenses. 1" Super Comat, Angenieux 10mm, a few others. On all these lenses, there is no provision to adjust the rotation of the lens in relation to the turret, so I thought it may have been a feature. It hasn't affected the use of the lenses, but it also means that every time I change a lens, I have to realign the threads to ensure I can see the focus/aperture index marks. That said, I also think that over 40-60 years, the metal may have just changed. Threads may be applied using an adhesive and/or heat to allow the thread to shrink as it cools onto a lens flange assembly. It's a lot cheaper to make a bare tube then add the thread to it later, than it is to cut the threads to locate the focus/aperture index marks for every lens.

Phil Forrest

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Is it a pre-set 10mm (with the aperture levers)? Early 10mm Switars have a fixed rear thread section that is part of the focus helical so the mount can't rotate independently but if my memory serves (Jean Louis Seguin would know) the later pre-set series have mount threads that are rotatable but spring loaded - so they take a bit of force to rotate but secure firmly once you tighten them on the camera. I haven't actually worked on a pre-set 10mm for a few years so I can't remember exactly, but I think this is the case.

If the spring washer under the mount thread assembly is deformed or missing or the lock ring is not properly screwed down then the mount can rotate more freely.

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