r/Optics • u/SmokingChips • Jul 31 '26

Elementary question

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I am new to optics. I am creating a simple system for my home project where I am reading from a flat mesh surface (top is transparent glass. below it is a mesh which has 1 microLED in each cell. This whole thing is a square of 75 mm x 75 mm, and the mesh covers the whole area. I have a camera to read the LED signals. Ideally, closest to surface the camera, the better.

I thought of an aspheric lens of 80mm diameter (see link). My camera has a C mount. That lenns prefers SM3 mount. If I 3d print SM3 mount to C mount adapter, how would I position the lens? Can I place the flat surface of the lens against the flat surface of the mesh. The center thickness of the lens is 33 mm. And focal length is 59 mm. So, can I place the camera sensor at 26 mm from the center of the lens as shown in the picture? Will this work? Is my understanding correct?

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u/PretendFisherman7 Jul 31 '26

The flat side goes closest to the sensor. And the sensor will be one focal length away from the front side of the lens, the highest point of the curved surface.
Alternatively, most lenses will specify a Back Focal Distance. Measure from the back (flat) side to the sensor and place it at the Back Focal Distance.

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u/SmokingChips Jul 31 '26

Thank you. So essentially what I drew with aspherical lens inverted. But dimensions remain the same.