Plano-concave spherical surface mirror, the reflective surface is a part of the spherical surface, and the parallel incident light rays can be converted to a point by the spherical surface reflection and have a positive focal length. The focal length of a plano-concave spherical mirror is half the radius of curvature of the sphere. 1T Optics provides uncoated and reflective spherical mirrors. The reflective coating options include ordinary protective aluminum film, protective UV reflective aluminum film, protective silver film, protective gold film or dielectric high-reflection film.