The zoom lens for still cameras
1959 (Voigtländer-Zoomar, the first for 35mm still cameras)
A lens that changes focal length while keeping focus. The Voigtländer-Zoomar of 1959 brought it to 35mm still cameras; by the 1980s zooms were the normal kit lens.
How it began
Variable focal-length lenses were used for film and television cameras from the 1930s. In 1959 Frank Back of Zoomar designed, and Voigtländer made, a 36–82mm zoom for 35mm single-lens reflexes, the first for still photography.
How it works
Groups of elements slide along the lens. One group changes the magnification, and another moves to compensate so the image stays in focus, so the photographer can frame by zooming instead of walking or changing lenses.
Why it mattered
Early zooms were heavy and less sharp than fixed lenses, but computer-aided design and better coatings made them good enough for nearly everyone by the 1980s. A single zoom replaced a bag of lenses for most photographers.
Limits and what replaced it
Zooms are bigger, slower or more complex than prime lenses of similar quality. Phones combine several fixed-focal-length cameras with digital cropping instead.
Today
Most interchangeable-lens cameras are sold with a zoom, and phones imitate zooming with several fixed lenses.