Field of view and focal length reduction

[radiometry]

Hi,

My simple telescope consists of a convex lens which images an area with diameter D into the detector diameter d. The object distance is S' and the image distance is s as indicated in the upper graph. Since S'/s=D/d, if I want a smaller field of view (a smaller D), I end with up a larger s and hence a lens with a larger focal length (lower graph). What's the easiest solution to reduce my telescope tube length while keeping the same field of view, a concave lens behind the convex lens? Many thanks.

 

[IRstuff]

Your problem is not sufficiently well-defined, and, I think, beyond the scope of this forum. You should consult an experienced designer

> FOV is defined by detector/focal length, so a smaller detector also results in a smaller FOV
> Have you considered a reflective optic?
> Theoretically, you would need a higher magnification convex, coupled by a concave, but unless you have specifics about image quality, distortion, etc., that's beyond the scope of a simple question/answer forum.

TTFN
faq731-376

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