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I have the following problem. I have a sensor with 1mm diameter and I need to have 500 urad (microradian) field of view. If I understand correctly, that would generally mean that I need to use 2meter focal length. However, I have 20cm space. It is acceptable to defocus the image if necessary. Can I achieve the required FOV for this sensor and distance at the receiver by using a combination of two or more lenses?

Thank you!

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What about folding your optical path with mirrors?

I don't know a good way to sketch it, but imagine adding 4 mirrors in the optical path. The mirrors arranged in two pairs roughly facing each other, but slightly angled and offset so that the light zig-zags between the mirrors. So, the light enters the lens, and is reflected back-and-forth between the 4 mirrors before hitting the detector.

This results in 5 passes of the light, which brings your length down to 20 cm.

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  • $\begingroup$ Oh, that deserves a thought. I was thinking for a two mirror system. Thank you! I will still wait to see if some lens approach will be proposed. $\endgroup$ – D. K. Mar 22 '18 at 2:02

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