spy camera lighter
what is the aperture diameter of the camera?
A spy camera is said to read up on the board of a number of cars on the license. If the numbers on the plate 5.7 cm apart, and the spy satellite at an altitude of 140 km, what is the diameter of the aperture of the camera? (Suppose the light with a wavelength of 550 nm.) ____m
According to the Rayleigh criterion (ref.) resolution angle theta = arcsin (1.22 lambda / diameter) for this problem theta = 1.22 lambda / d is sufficient, because theta is small. Theta = 0.057/140000 = 4.07143E-7 rad. Then diameter = 1.22 lambda / theta = 1.648 m. However, because 5.7 cm is the separation of the numbers, not the extent of the identifying characteristics of the songs, I would think it would take at least twice that resolution (and aperture) actually read the numbers. But without more details, The answer is all that can be said.
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