Spherometer

Gaertner spherometer is a precision made instrument to measure the radius of curvature of lenses. It has a weight balanced, zero force probe that pushes up against the lens surface, held at three points via an interchangeable lens holding platform. The bottom end of the probe carries a graduated linear scale, seen through a microscope with an adjustable reticule. The linear scale is illuminated by a built-in light source, and the measurements are read through the microscope with 0.01 mm accuracy. The modern version of this apparatus uses a digital scale, and a digital display to show the readout. There is a joystick-like lever that activates the probe to approach the lens from below.

Interchangeable measuring base for a cariety of lens diameters.