Dioptrimeter

an instrument for measuring the refractive power of an optical glass (glass in spectacles) expressed in diopters (D) and for determining the positions of the principal meridians of an astigmatic lens in spectacles. It consists of a collimator, an optical tube, a reading microscope, a mechanism for holding the lens being measured, and a mechanism for measuring the diameter of, centering, and marking the lens. The dioptrimeter makes it possible to determine the power of an optical glass with an accuracy of ±0.12 D.