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Re: [Phys-l] FW: Science show "Humanly Impossible" onNationalGeographic channel.




Dilated pupils --> larger aperature... What happens to SHARPNESS? Go play
with a pinhole camera, or look at the lens and f/stop settings on your SLR
camera. Or better yet, draw some ray diagrams comparing large and small
aperature openings.

Conventional ray diagrams are extremely misleading. They do not take into
account diffraction, which is a contributor to lack of sharpness. Actually
in the limit of a very large aperture the sharpness decreases dramatically
because the rays coming from the sides are actually coming from different
angles from the subject. So information from different angles are
superimposed which decreases the sharpness. Essentially the different angle
rays are superimposing different details on top of each other. So in
geometric optics the infinitely small pinhole is the best. But of course
film or optical sensors are not fast enough to accommodate this, and it does
not take into account diffraction.

Again, there are some simplifications in analysis which obscure the reality.

John M. Clement
Houston, TX