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I'm trying to use the Arducam 8mp with CS mount with a 25.4 C-Mount Filter, but I am unable to focus the picture. The filter fits perfectly and still leaves room for the lens to screw in.

It says in the second link that it can cause focus issues with some CS cameras, and the alternative seems to be a similar filter with a spacer. (also I can't find a seller for that model at the moment).

Would using a CS to C adapter fix this issue? Whats the cause of the focus issues, is the filter too close to the sensor? too far? Is the filter too close to the lens?

Any help is appreciated.

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    Possible duplicate of Can I use lens brand X on interchangeable lens camera brand Y? – Hueco Apr 16 at 22:57
  • I realize these scenarios are a bit different but the answer is the same. The lens is designed to be Xmm from the sensor (called Flange Focal Distance or FFD) and it appears that you're using a filter that fits between the sensor and the lens, thus the lens is pushed further out than it was designed. At the end of the day, you need to put the lens at the FFD for which it was designed or use some sort of adapter. – Hueco Apr 16 at 22:59
  • Thanks, you must be right. It seems like my best bet is to get a C mount lens with a larger FFD, and get a CS to C mount adapter. – jdavison Apr 16 at 23:03
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    There's really no flange, so i t would be more proper to call it registration distance (which is really more proper all of the time). – Michael C Apr 17 at 5:21
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Consider using filters that are placed in front of the lens.

The filters you are trying to use are installed between the lens and sensor. There are a few ways they could affect focus.

  • By increasing the distance between the lens and sensor.

  • By altering the light path so that it focuses in front of the sensor.

I would expect you'd have the same problem if you attempt to use the same filters with C-mount lenses and C-CS adapters. 

  • The lens has to be a certain distance from the sensor. The adapter makes up that distance. But if you put the filter between adapter and sensor or lens and adapter, you will have the same issues as before -- either lens will be moved too far or the filter alters the light path and affects focusing.
  • Why do you think I would have the same issue with a C mount lens and adapter? because the sensor itself is made to have the lens at a certain distance? or is the problem that the lens is made to have the sensor at a certain distance? – jdavison Apr 17 at 0:18
  • Lens has to be a certain distance from the sensor. Adapter makes up that distance. But if you put the filter between adapter and sensor or lens and adapter, you will have the same issues as before -- either lens will be moved too far or filter alters light path and affects focusing. – xiota Apr 17 at 0:45

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