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The elimination of distortion and coma in an image is met when
M = n sin u/n′ sin u′ or nh sin u = n′h′ sin u′where M is the lateral magnification, n and n′ the refractive indices of the media in the object and image space, u and u′ are the angular apertures on the object and image sides, and h and h′ the sizes of the object and image, respectively. Syn. Abbé's condition. See angular aperture; coma; correction; distortion.