I have built a custom optical device that uses a standard C-mount lens as found on CCTV cameras.
Wikipedia states that the flange-to-film distance of a C-mount lens is 17.526 millimetres.
I have built my device with roughly the same distance (about 18 millimeters) between the flange and the optical plane.
When playing around with the focus, I can focus objects as close as 30 centimeters, but not further than 2 meters, rendering the device effectively near-sighted.
My question is threefold:
- If I have built my device with the correct distance between the flange and the optical plane, does this mean the (inexpensive) lens I am using is bad?
- If not, is there a way to determine the right distance that I should use?
- If not, do I move the lens away or closer to the optical plane to fix the problem?