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Unformatted text preview: 6.2.1 Lenses The Gaussian lens formula can be deduced from Fermats principle with the approximations cos = 1 and sin = . For the refraction at a spherical surface with radius R holds: n 1 v-n 2 b = n 1-n 2 R where | v | is the distance of the object and | b | the distance of the image. Applying this twice results in: 1 f = ( n l-1) 1 R 2-1 R 1 where n l is the refractive index of the lens, f is the focal length and R 1 and R 2 are the curvature radii of both surfaces. For a double concave lens holds R 1 < , R 2 > , for a double convex lens holds R 1 > and R 2 < . Further holds: 1 f = 1 v-1 b...
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- Spring '10