Lenses and Mirrors

Lenses are transparent materials bordered by two curved surfaces or one curved and one flat surface. They are typically made of glass or plastic and are used to refract light and form images. Depending on their shape, lenses can be:

Converging (Convex): Thicker in the middle, converge parallel rays to a focus.
Diverging (Concave): Thinner in the middle, diverge parallel rays outward.

Mirrors reflect light. A spherical mirror is a portion of a sphere and can be:

Concave: Converges light to a focal point. (Mirror surface curves inward)
Convex: Diverges light. (Mirror surface bulges outward)

Plane Mirrors form virtual, upright images the same size as the object and located the same distance behind the mirror as the object is in front.

Nature of Images Formed

Object Position (u)	Image Nature	Image Orientation	Image Size	Image Type
u < f	Behind the object	Upright	Magnified	Virtual
u = f	At infinity	--	Highly magnified	Real
f < u < 2f	Beyond 2f	Inverted	Magnified	Real
u = 2f	At 2f	Inverted	Same size	Real
u > 2f	Between f and 2f	Inverted	Diminished	Real

This table applies primarily to converging (convex) lenses and concave mirrors. Diverging lenses and convex mirrors always produce virtual, upright, and diminished images regardless of object distance.

Written by Albert Marin