through-the-lens metering

(TTL) Cameras with built-in light meters date from c.1900, and cameras with meters to control the shutter or aperture from 1938. The first with TTL metering was Feinwerk Technik GmbH's Mec-16 camera of 1960. Although the Asahi Optical Co. (Pentax) had shown a prototype in 1960, the first production SLR camera with TTL metering was Tokyo Kogaku's Topcon RE Super (1963). The CdS cells on the back of the mirror made averaged readings at full aperture from c.7 per cent of the total light. Film speed, shutter, and aperture were all coupled. TTL metering—also for dedicated flash—is standard on most modern cameras.

— Michael Pritchard

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