There are plenty of major milestones in the history of the 35mm SLR, particularly when it comes to the integration of increasingly more and more automation. Of course, there were a number of important mechanical milestones along the way, including the pentaprism-based viewfinder – which delivered a correctly-orientated image – and the instant return mirror along with automatic shutter recocking.
However, it was the incorporation of built-in metering which represented the first big step towards more convenient – and potentially more accurate once the measurements were made through-the-lens (TTL) – exposure control. Once stopped-down metering – which required that the taking aperture be preset – was superseded by open-aperture measurements, the next step was to use this communication from the lens to the camera body to facilitate semi-automatic exposure control.
