The photoelectric exposure meter
1932 (Weston Model 617)
A hand-held meter whose selenium cell turned light into a small current, so photographers could measure exposure instead of guessing from tables.
How it began
Before meters, photographers judged exposure from experience, printed tables or extinction meters that relied on the eye. In 1932 the Weston company sold a meter built around a selenium cell, which makes a current when light falls on it.
How it works
The cell’s current grows with the brightness of the scene, and a needle shows it. A dial then converts that reading into pairs of aperture and shutter speed for the speed of the film loaded.
Why it mattered
It made exposure a measurement. It also led directly to meters built into cameras and then to automatic exposure.
Limits and what replaced it
Selenium cells were bulky and weak in dim light; CdS and silicon cells followed, and from 1963 meters moved behind the lens. Today the camera’s own sensor does the job.
Today
Almost every camera now meters by itself; hand-held meters live on in studios, cinema and film photography.