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Taking a meter reading from a part of the scene that does not include the sun is one way to ensure a proper exposure. Look for a good middle tone. Where in the scene would you meter?

Have you ever observed a photographer put the palm of their hand in front of the camera lens while looking through the viewfinder? You overhear them say something like “I'm metering my hand and opening up 1-stop.” Huh? Unwilling to appear like an ignorant photographer, you nod your head, mumble something that sounds like approval and turn your camera dial to the green idiot box, since you haven't the faintest idea what they are talking about.

If you've been hanging in there with this column, the days of joining the ranks of the “knowing” shooters is getting nearer.

We've covered a lot of informational territory in this column. We have discussed the function and control of aperture and shutter and their use in determining exposure. We have gone through the steps of understanding light and reflectance and that varying values of light in a scene determine contrast. We've learned how cameras come to suggest an exposure setting and the variables we must consider when overriding that suggestion. This column, and the next couple, will put this information all together and show how it is used to take a properly exposed image. Ready? Lets get on with it.

We know that camera meters insist on rendering a scene as a middle tonal value, or drab gray. Unless you live in Minnesota in the depths of winter, which I have, scenes around you are not drab gray. We are, therefore, forced to understand reflectance and control the camera in determining exposure.

Ansel Adams (1902-1984), known for his incredible black & white photography of Yosemite Valley, created the Zone System technique for mapping tonal values to exposure values. The system identifies a range of 9 stops of light for recording detail in a scene. Zone V, is smack dab in the middle of the range. Point your camera at any object and the meter recommends a combination of aperture and shutter speed to render that object at Zone V. Knowing that, the photographer then has the opportunity to modify the exposure, placing the object on a zone that makes more sense.

For example, point the camera at a white wall. The camera meter, lets say, suggests an exposure of f/16 at 1/500 of a second. This is the cameras attempt to render the wall at Zone V, or 18% gray. Being the intelligent photographers that we are, we say to ourselves, “this is a white wall, not a gray wall. I need to provide more exposure to render this wall properly.” But, how much more exposure? Referring to Table A, we see that in order to render white objects as white, the exposure of the white wall should be placed on Zone VIII, or 50% reflectance. Zone VIII is 3 stops more exposure then Zone V, so adjusting the recommended exposure to f/16 at 1/60s is the way to go.

Next time, we delve a bit deeper into the derivation of the Zone System and why it maps so readily to exposure and stops of light. Just a caution, read the next column with a full cup of coffee. Until then, keep shooting.