How can I make a tiny fixed-focus camera focus at 10–20mm instead of about 100mm?

Question

I’m using a very small OmniVision OVM6211 camera module with a built-in lens stack. It has roughly a 90° field of view and currently focuses from about 100mm. For a science experiment, I need a fixed working distance of about 10–20mm.

I’m considering adding an external lens in front of the camera, with a custom holder if needed. I don’t need perfect image quality, but I do need the subject to be reasonably sharp and I’d like to keep most of the wide field of view.

Is adding a single lens a practical way to reduce the focusing distance by 5–10×? If so, what kind of lens should I look for?

user32811 · Answer

Any converging lens will bring you closer to the target, you need to find a small magnifying glass or loupe (available online everywhere for a dollar or two).

In fact, the conditions are equivalent to a human eye trying to focus at close distance. Test the lens by placing it between your eye and the subject, see if you can focus from 10-20mm.

Small, good quality lenses can be found in some optical accessories, here I'm disassembling the SkyWatcher telescope eyepiece (10mm focal length Plossl, consists of 2 tiny achromatic lenses).

Now about the image quality... I doubt it can be perfect using such simple setup, try and see if it is good enough for your purposes.

btw. I'm doing this all the time, doing macro shots using my old fixed focus webcam.

How can I make a tiny fixed-focus camera focus at 10–20mm instead of about 100mm?

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