R Measuring Interferometer / DTM-RMFI

It is a device that uses an interferometer and measures the radius of curvature of the concave surface of the small curvature.
There are two positions where can be observed interference fringes reflected on the concave surface. One position is that the focus is on a concave surface of the achromatic lens, and the other position is that the focus is on the center of curvature of the concave surface. When reading the micrometer on the stage carrying the sample, the distance between the two positions can be observed the interference fringes of concave sample, and it can be used to determine the precise radius of curvature.