On Mon, 23 Dec 2002 02:25:25 GMT, AC/DCdude17
wrote:

>How can the light meter on cameras measure proper exposure without
>knowing the spectral response curve of films used?
>
>Let's say you want to photograph under monochromatic low pressure sodium
>lighting using panchromatic film. Since the light is almost pure 589nm
>sodium line. To get a proper exposure, the light meter needs to know the
>response characteristic of photographic emulsion to this spectra.

Yes. Under most conditions, the color saturation
of the metered material is low enough, and the
spread of colors is great enough, to average out
meter color errors. Common exceptions: the one you
cite, using colored filters in B&W, and shooting
flower close-ups where yellow, orange, and red
may be saturated and may predominate in the metered
area - these require compensation... BTW, the old
selenium-type meters have fewer problems with
color-error than "modern" cell types...;-) It is
interesting to see that most consider this to be
not a problem - but a simple test with colored
filters of known filter-factor will convince one
quickly that meters can be off rather noticeably
due to color error alone...;-)

David Ruether
d_ruether@hotmail.com
http://www.David-Ruether-Photography.com
Hey, check out www.visitithaca.com too...!