p35_061

# p35_061 - W 2 /f 2 = W 1 /f 1 follows immediately. (b) The...

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61. (a) Parallel rays are bent by positive- f lenses to their focal points F 1 , and rays that come from the focal point positions F 2 in front of positive- f lenses are made to emerge parallel. The key, then, to this type of beam expander is to have the rear focal point F 1 of the Frst lens coincide with the front focal point F 2 of the second lens. Since the triangles that meet at the coincident focal point are similar (they share the same angle; they are vertex angles), then
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Unformatted text preview: W 2 /f 2 = W 1 /f 1 follows immediately. (b) The previous argument can be adapted to the Frst lens in the expanding pair being of the diverging type, by ensuring that the front focal point of the Frst lens coincides with the front focal point of the second lens. The distance between the lenses in this case is f 2 − | f 1 | (where we assume f 2 > | f 1 | ), which we can write as f 2 + f 1 just as in part (a)....
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## This note was uploaded on 11/12/2011 for the course PHYS 2001 taught by Professor Sprunger during the Fall '08 term at LSU.

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