The principal focus of a concave mirror is a point on the axis of the mirror at which parallel rays of light are brought to focus after being reflected by the mirror. A concave mirror is a mirror with a curved surface that is shaped like the inside of a bowl, with the center of the curve facing outward. When light rays are reflected by a concave mirror, they are brought to a focus at the principal focus of the mirror. The distance from the center of the mirror to the principal focus is known as the focal length of the mirror. The principal focus of a concave mirror is an important concept in optics and is used in the design and operation of various optical instruments, such as telescopes and cameras.