Patent ID: 7230693

Claim:
A lens meter for measuring optical characteristics of a subject lens to be measured, the lens meter comprising: a measurement optical system including: at least three spot light sources for measurement disposed equidistant from a measurement optical axis of the measurement optical system; a projecting lens; a diaphragm having an aperture disposed at an anterior focal point of the projecting lens between the light sources and the projecting lens, a diameter of the aperture of the diaphragm being variable; and a two-dimensional photodetector which photo-receives measurement light bundles from the light sources passing through the subject lens after passing through the aperture of the diaphragm and the projecting lens to detect images of the light sources, wherein the projecting lens is disposed so that the light sources have a conjugate relation with the photodetector in a case where the subject lens with one of a specific diopter in the vicinity of 0 D and a frequently-used specific diopter is placed at a measurement position on the measurement optical axis; and control means for obtaining one of a difference of a light amount in the image of the light source and the number of the detected light source images based on an output from the photodetector, and changing the diameter of the aperture of the diaphragm based on a result of the obtainment.