Sequence viewing > Photographic Exposure - Resource - © Lloyd Godman

What is a light meter?

CDs Light Meter


This type of meter is externally similar to the selenium cell meter, but it has a smaller cell. It is driven by a battery instead of a solar cell. Cds or Cadmium sulphide cells are photo-resistance; meaning that its electrical resistance changes in proportion to the light it receives. This type of meter is much more sensitive and can even give readings in moonlight but only work when the battery is circuit.

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A supplementary light diffusing dome fits over the cell or slides along to cover it is often included for incident light readings which are readings from the light rather than the subject
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However they are rather slow to register their readings and bright light conditions tend to be remembered by the cell for some time, so you may have to wait a few minutes after measuring in bright sunshine before using the meter indoors. They may slightly over respond to red. Note a red needle indicates a number on the scale which is then transferred by turning the dial to match the number. The scale can be changed from high to low by moving the slide at the top of the meter. Once the dial is rotated to match this number the aperture setting (lower figure) and a the shutter speed (upper figure) can be selected from the dial.

Like all light meters, remember to set the film speed.

 

 

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