| 摘要 |
PURPOSE:To execute a diopter adjustment of about -1.5-+1.5 diopter by constituting the titled optical system of a first lens of a convex negative meniscus lens and second lens of a biconvex lens, fixing the second lens, moving the first lens in the optical axis direction, making the diopter variable, and satisfying various conditions. CONSTITUTION:The titled optical system consists of a pentaprism 2, the first lens of a negative meniscus lens being convex to a finder screen side, and the second lens of a biconvex lens in order from the finder screen side, and the second lens of a biconvex lens in order from the finder screen 1 side in a single-lens reflex camera, the second lens is fixed, the first lens is moved in the optical axis direction and the eyesight is made variable, and also, expression are satisfied. In the expressions, n2 and n3, r4, r5, f-1, and fI denote refractive indexes of d line of the first and the second lenses, respectively, a radius of curvature of a second surface of the first lens, a radius of curvature of a first surface of the second lens, a focal distance of the whole system at the time of -1 diopter, and a focal distance of the first lens, respectively. In such a way, the diopter adjustment of about +1.5--1.5 diopter can be executed, and also, the performance for various aberrations is satisfactory, and with respect to a shift of an eye, the disorder of an observation image is reduced.
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