Concave and Convex Mirrors

Curved mirrors, focus and the mirror formula.

Spherical mirrors are pieces of a hollow or bulging sphere. The centre of that sphere is the centre of curvature C, and the focus F lies halfway between C and the pole P of the mirror on the principal axis.

A concave mirror brings parallel rays together at a real focus and can magnify a close object. A convex mirror always spreads rays apart and gives a smaller, upright, virtual image, which is why it is used where a wide field of view matters.

• Focal length is half the radius of curvature: f = R/2.
• Concave mirrors converge light and can form real or virtual images.
• Convex mirrors diverge light and form only virtual, diminished images.

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