A pinhole camera doesn\'t have a lens; a small circular hole lets light into the

Question

A pinhole camera doesn't have a lens; a small circular hole lets light into the camera, which then exposes the film. For the sharpest image, light from a distant point source makes as small a spot on the film as possible. What is the optimum size of the hole for a camera in which the film is 16.9 cm from the pinhole? A hole smaller than the optimum makes a larger spot since it diffracts the light more. A larger hole also makes a larger spot because the spot cannot be smaller than the hole itself (think in terms of geometrical optics). Let the wavelength be 571 nm.

Explanation / Answer

D = 16.9 cm , lamda = 571 nm

from Rayleigh criterion

= 1.22/D

= 1.22*571*10^-9/0.169

theta = 4.12*10^-6 rad

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