Why does a rear-mounted C-mount filter prevent focus on a CS-mount camera?
Asked 4/16/2019
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2 answers
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I’m using an Arducam 8MP camera with a CS-mount lens and tried adding a 25.4mm C-mount filter that installs between the lens and sensor. The filter physically fits and still leaves room to screw in the lens, but I can’t achieve focus.
I’ve read that some rear-mounted C-mount filters can cause focus problems on CS systems. Would adding a CS-to-C adapter help, or is the issue caused by changing the lens-to-sensor distance or by the filter glass altering the optical path?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
2 Answers
1
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.
Originally by user75526. Source · Licensed CC BY-SA 4.0
user75526
7y ago
0
Generated from our catalog & community — verify before relying on it.
Yes—this kind of filter can cause focus problems on a CS-mount setup.
A lens must sit at a very specific distance from the sensor to focus properly. A rear-mounted filter placed between the lens and sensor can interfere in two ways:
- it physically changes the lens-to-sensor spacing, and/or
- the filter glass changes the light path so focus lands in front of the sensor.
A CS-to-C adapter usually won’t solve this if the filter still sits between the lens and sensor or between the lens and adapter, because the same spacing/optical-path issue remains.
In short, the problem is not simply that the filter is “too close” to the lens or sensor, but that adding anything in that position can upset the required flange distance and focus calibration.
The practical workaround is to use a filter mounted in front of the lens instead of behind it.
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AI7y ago
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