On Tue, 24 Dec 2002 12:55:01 -0500, Alan Browne wrote:

>The light meter in a TTL camera (or handheld meter) is very wideband and
>flat for the light across the visible spectrum (perhaps a bit
>more/perhaps a bit less). Except for minor discrepencies in sensitivity
>accross those wavelengths, the meter is for practical purposes flat. If
>you measure monochromatic light with it, you will still get the
>contribution of that light and get an exposure that is close to the
>meter reading.
[...]

The color response of many camera meters is so different
from film response that obviously-wrong exposures occur
if the meter reading is followed, without compensation.
On one side, using a number 25 red filter with a TTL
meter will about guarantee considerable underexposure;
on the other, photographing a nearly pure-red tulip
or car that occupies almost the entire frame will also
about guarantee underexposure. It is useful to do some
basic tests with a grey card and colored filters or
strongly-colored subjects. Afterwards, it is hard to
believe what you said (and, as others have pointed
out, our sight, film, and meters are not flat-response,
though some attempt is made to make the last two
*approximate* the first...).