With spherical mirors, the focal length is inversly proportional to the sum of distances:
(1/f) = (1/di) + (1/do)
(Bauer and Westfall, pg 1035)
There are two kinds of spherical mirrors: concave or converging, and convex or diverging.
Examples:
Concave:
A concave mirror is known as converging because the rays all converge on one spot.
(Stoner, Ellen. "Mirror Ray Tracing")
This is only one way that an image in a concave mirror may appear. The image may be:
large and upright, large and inverted, the same size and inverted, or as shown: small and inverted.
Convex:
A convex mirror is know as diverging becasue the rays diverge.
(AZo Optics - The A to Z of Optics)
Home
References