You camera meter assumes that the light is bouncing off of an 18% gray subject. If the subject is darker than that the meter will over expose, if lighter the meter will under expose. So let's say you see a white rock and a black rock sitting side by side. The light falling on them is the same, so one camera setting will result in the correct exposure for both. But you camera's meter will be fooled by the tonal differences - the light reflecting off the white object will result in a recommended setting that will result in under-exposure. The black object reflect back less light, and tricks your camera into recommending an exposure that will be over exposed.
An icident meter will measure the light directly - no reflectivity factor. Put it over the white object and then again over the black object, and the meter reading will be the same - because it is reading the light directly. Or put a gray card into the scene - the gray card is the exact reflectivity that the camera expects - and meter off that.
the obvious drawback is that you have to be near the subject to use an incidnet meter. So with a telephoto, where you may be poking into a shadow here and direct sun there, it's not practical. But if the subject is still you can almost always get a good incident reading - either by going to it and reading or, for larger subjects under consistent light, just taking a reading where you are. If I'm shooting on a beach or a field and the light is pretty consistent, a hundred yards or so won't make a different in the light, and I can meter where I am for what I'm shooting. Not so in a city or the woods, though.
- MCC
At 06:59 PM 3/24/2003 -0500, you wrote:
OK, I'll ask the obvious question and "expose" my true ignorance. Why is the incident light a "better" reading? After all, it's reflected light that going to hit the film, no matter what is hitting the subject. It's also the reflected light that hits my eye.
Always wanted to ask this question . . .
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Mark Cassino
Kalamazoo, MI
[EMAIL PROTECTED]
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Photos:
http://www.markcassino.com
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