Here's some follow-up on metering that to me makes mastering exposure worthwhile.
Moving light values around—it’s an odd idea, but one that allows you to make creative choices about how light is recorded. You can work to get as much visual information and tonal richness as possible, or you can eliminate certain values for graphic effects. Though it's usually best to go for the former, the ability to juggle recorded tonal values is a key creative element in photography that brings a personal touch to an often forgotten skill—seeing and interpreting light as you shoot.
One of the ways to begin the process is to shun the “matrix” or “evaluative” metering pattern. Not that there’s anything incorrect or faulty with that pattern; it’s just that we want to be able to direct the exposure system to read values as middle gray. Move on over to spot metering pattern.
If you spot meter off a bright area in a tonally-varied scene and do nothing, the bright areas will record as middle gray and the darker areas will be compressed down into darker and darker tones. Conversely, if you meter and expose for the darkest area in the scene the brighter areas record brighter on film and may be driven up into overexposure. Think of the tonal scale as working in lock step, with the ability to record a range of values as having a fixed spread that can be moved up and down the grayscale “spectrum” of brightness values.
Once this idea becomes real to you the path toward being able to manipulate light should open. You can, as mentioned, read only from a bright value and record that as middle gray, and have the darker areas lose detail and become dark tones. Or, you can read the bright value as middle gray and then compensate exposure by opening up two stops; thus the birghter value will record as bright with texture and visual information. Or, you can open up three stops and have that value record as bright, textureless tone. (For example, plus two would keep the texture of wood in a brightly lit white picket fence; plus three would give you pure, driven snow.)
Conversely, you can read the significant shadow value and have it record as middle gray, which will make the brighter values record brighter still (or perhaps become overexposed.) You can also read the dark value as middle gray, close down two stops to have detail recorded in that dark value. Or, or you can use that same reading, close down three stops and just get a deep tone with virtually no visual information. In these ways you control what is recorded with detail, and what records as dark or bright tones without detail. Compensation is not limited to working with two stops--you can manipulate values by one stop, or by half stops if that serves your purposes.
The above assumes you are working in an autoexposure mode, like aperture priority. If you prefer working in manual so much the better, as you can dispense with using the exposure compensation and exposure lock features on your camera.
All this gives you control over highlights and shadows, and how the scene you have in front of you will record. Once you grasp the concept of value and tonal manipulation you have a wide range of choices that allow you to shape the exposure in many ways.
Spot metering for the highlight in this shot "drives down" the darker values into deep shadow, or pure tone.
Image and text copyright: George Schaub
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