PURPOSE:To shorten the overall length of a finder optical system by introducing aspherical faces to the shapes of lens faces in order to assure the degree of freedom in correcting aberrations. CONSTITUTION:A titled finder consists of the negative 1st lens, the negative 2nd lens having strong curvature on the pupil side and the positive 3rd lens, successively from an object side, wherein a pupil is placed behind the same. A frame of a field range is provided on the object side face of the 3rd lens and the pupil side of the 2nd lens is constituted as a semitransparent concave mirror. The faces of the 1st, the 2nd and the 3rd lenses on the pupil side are formed into the aspherical shapes expressed by the equationIwhen (c) is defined as paraxial curvature, (k) as the coefft. of quadrics, A4, A6, A8 are defined as the coeffts. of aspherical faces of higher order, and (y) is defined as the height from the optical axis, wherein the quartic coefft. of (y) is expressed by the equation II in consideration for the contribution by the coefft. of quadrics. The aspherical face of the rear face of the 1st lens in this case is so formed as to satisfy the conditions of the equation III, the aspherical face of the rear face (half mirror part) of the 2nd lens, as to satisfy the equation IV and the aspherical face of the rear face of the 3rd lens as to satisfy the equation V, respectively.
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