Information on the types of meter, what is being measured, different methods of calibrating film speeds and film speed comparisons.
Simple exposure guides were often included in books of the period or supplied by manufacturers in boxes of film. Popular forms were included in diaries. More elaborate examples had sliding or revolving scales.
Actinometers or tint meters use sensitive paper to gauge the light. Popular especially in Britain from the 1890s to the 1930s, popular models were the Wynne and Watkins.
These were popular in the 1920s through to the 1950s. The light is judged by what is 'just visible' when looking into the meter. The tubular form, where the photographer looked into an eye-piece, was very popular in the 1930s. The open pattern was popular for a short time in the 1950s, it was cheap and answered the need of the rising number of amateur photographers.
Popular from the 1930s onwards; increasingly found built into cameras and coupled to the shutter and diaphragm settings.
The scene is compared to a standard light source such as a bulb. These designs were never popular with amateur photographers but were used professionally as spot meters from the 1950s.
Sensitometers and Densitometers were mainly used by commercial emulsion manufacturers but simplified forms were used by photographers to test sensitive plates and processes.
These are specialist meters for assessing the colour temperature (warm, cool) of the light.
Illumination Meters are non-photographic meters typically used to measure light levels in buildings. Late, photoelectric, models share many of the characteristics of photographic meters and are often mistaken for them.