StellarTypes of Mirrors & Focal Points
The most basic kind of mirror is a plane mirror. Plane mirrors are just flat mirrors that reflect light and have no curvature. The focus point of a mirror is where all of the light either converges to or seems to diverge from. Since a plane mirror is flat, its focus point can be thought of as being infinitely far away from the mirror since the light will never converge to a certain point nor appear to diverge from a certain point. The focus point is denoted with the variable .
A converging (concave) mirror will reflect all of the incoming light to a fixed point, known as the focus point. In a spherical concave mirror, the focus point will just be half the radius of the sphere that the mirror would be forming.
A diverging (convex) mirror will reflect all of the incoming light in a way where it looks like all the light could have originated from a single point behind the mirror, which is known as the focus point. In a spherical convex mirror, the focus point will just be half of the radius of the sphere that the mirror would be forming. The image below shows the difference between a converging and diverging mirror.