Ring spherometer
A ring spherometer is a measuring device used to determine the radii of curvature of spherical lenses . It essentially consists of a flat hollow cylinder on which the lens can be placed centrally. In the center of the hollow cylinder is a measuring sensor with which the lowering or curvature can be determined relative to the zero position. The zero position can be set by placing a plane-parallel plate on the spherometer and using it to calibrate the probe.
The radius of curvature can be calculated from the measured depression or curvature t and the inner or outer diameter of the ring d. According to the Pythagorean theorem :
