Light
Meters
Taking more accurate exposure readings is done with a light meter.
All meters work on this basis of converting light into electric current,
which can then be measured on a scale and translated into appropriate
shutter speeds and f numbers relative to the film ASA. While some meters
work on this basis of converting light into electric current like a
solar panel, others have a battery which provides power to a Cds or
Cadmium sulphide cell which are photo-resistance; meaning that its electrical
resistance changes in proportion to the light it receives.
Selenium
Cell light Meters
With
some meters, to help improve accuracy the needle moves over
two scales, 'high' and 'low'. In bright light conditions a perforated
flap restricts the light and numbers are read from the high
scale. Under dimmer conditions, this flap is removed and the
reading taken from the low scale. |
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Some
of these meters also allow the insertion of a invercone that
fits over the cell for taking incident readings. |
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