an outing at Craighleith beach in the 1950s – a Kodak moment!
Toronto. Photography by its very nature demands a certain amount of light. Surprisingly, measuring light was not an easy task until well into the last century. From photography’s inception, books and pamphlets gave suggested lens settings and timings for a variety of outdoor scenes. In fact, large companies like Kodak added an instruction sheet to each roll of film well into the last century.
Calculators came along to simplify the decision of exposure. Some meters were invented that let the amount of light determine the suitable camera settings. One such meter was the extinction meter. You looked at the subject while peeking in the meter and used the barely visible number as a reference. Unfortunately, the human eye grows quickly more sensitive in darkness possibly making the reading erroneous.
When selenium cell meters came along, for the first time the amount of light could be converted to electricity to cause a meter to record a setting. Great for daylight, but no value in dim light situations. And the size of the selenium cell was large.
This changed with cadmium sulfide (CdS) cells. In their case the resistance varied with the light rather than any current being created. With a suitable circuit and battery, the light meters worked well into the darkness.
Initially selenium and later CdS cells were used in meters that slid into accessory shoes and connected (usually) with the shutter dial. Setting the shutter would allow the meter to show the necessary f/stop for a given film speed. In time these became built-in meters, automatically changing the camera settings so the camera had to be set to ‘aperture priority’, ‘shutter priority’ or ‘program’ (a pre-selected sequence of shutter and lens settings).
Today smartphones do this automatically, freeing the photographer to concentrate on the subject matter and framing.
