A plane mirror produces a virtual image located as far behind the mirror as the object is in front of the mirror. The image is the same size as the object so the magnification of a plane mirror is 1.0 .

Incoming, parallel rays of light will be reflected by a spherical, concave mirror so they pass through a point called the focal point. Such light reflected by a spherical, convex mirror will appear to have originated at a point called the focal point.

Image formation may be understood by close observation of three principal rays that are easy to follow or to draw. All other rays will be bent (reflected by a mirror or refracted by a lens) to pass through the image position established by these principal rays.

Incoming, parallel rays of light will be refracted by a converging lens so they pass through a point called the focal point. Such light reflected by a diverging lens will appear to have originated at a point called the focal point.

The distance from the mirror or lens to the focal point is the focal length.

A concave mirror or a converging lens can produce either a real image or a virtual image depending upon the position of the object. The real image will be upside down and the virtual image will be right side up. The size of the image may be smaller or larger than the size of the object according to the position of the object.

A convex mirror or a diverging lens can produce only a right side up, virtual image of reduced size.