In the polishing process, a glass raw material is processed into glass for a lens filter, just as a raw stone is polished up into a gem.
The lens filter exists on the way of a light beam delivered to the film and photographing element. Even a slight distortion of the lens causes impact on the photograph image. Even a small irregularity on the surface results in diffused reflection of light.
In order to process the surface of the lens filter completely flatly, polishing is performed by a special machine.