When put the lens on a lens called a prototype, you'll see the interference fringes of Newton's rings.

The gap between surfaces below microns will form interference fringes of light, and different overlapping effects of reflected light waves will form different fringes, which are called Newton rings. In order to check whether the curvature of the lens after fine grinding meets the specifications, the lens needs to be placed on the lens called the original, and the curvature quality of the lens can be judged by observing the Newton ring, i.e. interference fringes, from above.