The first SLRs had clip-on external light meters, and those meters eventually became standard components. Unfortunately with interchangeable lens cameras, the meter’s coverage only matched the standard lens and perhaps a 35mm wide-angle lens. It wasn’t through-the-lens (TTL) metering, but at least it eliminated the need to carry a separate light meter. The Topcon RE Super (1963) was the first SLR that had TTL metering.
In the early days, you would focus at full aperture for accuracy and then stop down the lens to taking aperture for metering. Or you could meter first and then focus if your camera supported a diaphragm that would automatically close down when you took your picture. The next step was obvious: TTL metering, automatic diaphragm, and a linkage that let you meter with the lens wide open. That was another innovation of the Topcon RE Super.
Contrast Light Compensation
Introduced in 1966, the Minolta SR-T 101 introduced a unique metering system designed to overcome a problem with simple average metering. If there was too much sky in your photo, and averaging meter would underexpose everything else. Minolta’s innovation was to use two meter cells, one for the lower portion of the photo, the other for the higher area (which was often that bright sky).
The camera would compare the output of the two Cadmium Sulfide photo cells. The genius of this system is that rather than use some complex circuitry to calculate an ideal exposure, the cell metering the bottom of the photo was twice as sensitive, so when the output of the two cells was averaged, the foreground had approximately one stop more weight than the sky.
Further, for other types of photography, CLC was not significantly different from an averaging meter. It remained a feature of the SR-T family of cameras until the last models were discontinued in 1981. CLC was also used on Minolta’s first professional system SLR, the XK/XM/X-1 designed to compete with the Nikon F2 and Canon F-1. Unlike its Nikon and Canon competition, the XK was a system camera with automatic exposure.
Most of the industry adopted center-weighted metering, although Canon used a central metering pattern thay only measured about 11% of the screen. Minolta switched to a center-weighted metering system when it introduced the XD and XG lines in 1977.
An even more sophisticated type of metering system was introduced with the Nikon FA in 1983. It was the first camera to meter various parts of the screen and use a microprocessor to calculate the optimal exposure for the scene. With today’s digital camera, it is possible to evaluate every pixel, but it all began with CLC in 1966.
The SR-T 101 remained in production with only minor changes until 1975. It was phased out, along with the SR-T 100 and SR-T 102, to make way for a new set of models with a slightly different feature set, including a hot shoe for flash. Minolta made a second round of minor feature changes in 1977, but the core of the camera was virtually unchanged for 15 years, and many parts traced their origin to earlier Minolta SLRs without TTL metering.