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Unformatted text preview: among the focal length, the lens diameter, and the spot size. Take the f-number of the lens to be roughly 0.8 or 0.9, which is just about what you can expect for the fastest lens. 4. Popular legend has it that military spy satellites can read the numbers on car license plates. Your professor has no security clearance but he imagines it would be difficult for spy satellites to fly below about 100 km because of residual atmospheric gases. He also knows that the Hubble telescope was in its heyday reckoned a great honking big space telescope, and that its diffraction-limited images are collected with a primary mirror of diameter 2.4 m. If the Hubble telescope flew as low as 100 km (it typically flies at more like 500 km altitude), and if it was pointed down towards earth, instead of up at the sky, what is the smallest separation that could be resolvable on the surface of the earth? How does that compare to what you would need to read license plates?...
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- Fall '06