On Tuesday, March 4, 2003, at 07:09 PM, Thomas Bryhn wrote:
Normally we use the approximation f/# = f/D, more correct would be f/#
=
n1/(n2*2*sin(t)), where n1 and n2 are indexes of refraction and t is
the
angle spanned by the edge of the front element and the optical axis,
seen
from the point where the optical axis intersects the film. n1=n2 for
our
applications with air on both sides of the lens.
Thanks Thomas, I'd heard of the f/0.5 limit a few times, but this is
the first time I'd seen an explanation as to why. I've got a 50mm
f/0.7 C-mount lens at work (Fujinon, I think), which is getting close!
Mark.
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