After an overview of spherical and parabolic mirrors, let's study some technic terms about the spherical mirror.
1.P, pole, which is the center of the mirror
2.F, focus
3.f, focal length, which is the distance between P and F, f=R/2
4.R, radius of curvature, which is the radius of the (imaginary)sphere
5.C, center of curvature, which is the center of the sphere
6.Principle axis, all the light rays that could gather at the focus after reflection are all parallel to it
7.Aperture, which is the diameter of the mirror