There seems to be a limit, around 0.33, on the fastest possible aperture of a photographic lens made of glass. Is there a theoretical limit on the minimal focal length of a photographic lens (rectangular projection, not a fisheye)? Are the physical reasons that would prevent a, say, 1 mm focal length lens for a full frame sensor?
I also asked this question on Photography SE, but didn't get quite the answer I was looking for.
Just some thoughts...From the Wikipedia article Lens, we have the Lensmaker's Equation for a single lens:
where f is the focal length, n is the material index of refraction, d is the thickness and R1 and R2 are the radii of curvature. Let's for simplicity consider a plano-convex lens, with R2 infinite. The equation then reduces to f = R1/(n-1). So smaller and smaller f can be achieved with smaller and smaller radius of curvature, which implies smaller and smaller aperture since you can't have a big lens with a small radius. There doesn't appear to be any theoretical limit here.
Now if we are talking about a very short focal length photographic lens, it would have to be positioned very close to the sensor in order to achieve focus, which I would think would lead to handling and mounting issues.
