Automatic lens meter

Abstract

An automatic lens meter for measuring a pherical power, a cylinder power, an angle of cylinder axis, and a power of prism of an ophthalmic lens. The automatic lens meter is characterized by the use of a shading device to obtain the coordinates of the points at which respective light rays emitted from respective pin-holes of a multiple-pin-hole disc cross the second focal plane of an objective lens, according to a shading time lag among respective light rays. The shading device comprises a pair of deviated prisms respectively having substantially an equal apical angle, and disposed at a given spacing from each other between a lens set having an objective lens and a collector lens, with the apical angle of one prism directed opposite to that of the other vertically with respect to the optical axis; a rotary mechanism for rotating the pair of deviated prisms about the optical axis of the lens set at a given rate; a device for reading an angle of rotation of the pair of deviated prisms; and, a shading disc disposed at the rear of the pair of deviated prisms on the second focal point of the objective lens, and having opaque portions and transparent portions defined by two lines crossing at a right angle to each other at a point on the optical axis of the lens set.