As light darkened
silver - light meters were produced where a strip of photosensitive
paper was placed in a card calculator and the time taken for it
to change colour gave an indication of the length of time the
film should be exposed for. - Below is the imperial exposure meter.
 |
Another
form of exposure meter had a viewing window with a graduated
transparent material - when the operator looked though the
window the part of the transparent material that was most
easily viewable give a reading as to the exposure. |
Of course - these systems were open to a wide range of idiosyncrasies
and often quite inaccurate - so what was needed was a much more
reliable way of reading the intensity of the light source. In
1932 the first light meter with photoelectric cell introduced.
