Telephoto Lens
A lens with a focal length longer than the format's diagonal, magnifying distant subjects and narrowing the angle of view.
Measured in
mm
In depth
Strictly, 'telephoto' describes an optical design shorter than its focal length, achieved with a negative rear group; loosely it means any long lens. The narrow view isolates a subject, and shooting from further away flattens apparent depth, stacking foreground and background together. Long lenses also magnify camera shake in exact proportion to focal length.
Examples in practice
A 300 mm lens picks a single deer out of a herd and renders the hillside behind it as a smooth wash of colour.