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on Jun 24, 2009 in Tech Tips

Exposure

Exposure can be one of the most difficult aspects in photography to master. Even if you’re fortunate enough to own an F5 with its RGB meter, you still must understand exposure. Meters only give advice, you must know if it’s good or bad advice. Further more, being a photographer you must be able to communicate what you see to others. This requires a firm understanding of exposure and exposure compensation.

Coming to terms with exposure compensation requires understanding basic ambient exposure first. Ambient exposure is made of a combination of shutter speed and aperture (assuming no flash is in use). Using basic daylight (called the sunny 16 rule by some) your base exposure can be quickly calculated by combining f/16 and the reciprocal of the ISO in use (this is a sunny day exposure). For example, with ISO 100 film, your exposure should be 1/125 at f/16, or any combination that equals the same value (i.e. 1/60 at f/22 or 1/250 at f/11). This by the way, is an easy way to determine on your own if your camera meter is providing accurate readings. With your hand fully lit, take a meter reading off it and it should equal basic daylight (within 1/3 stop).

Now every meter, spot, center-weighted and even matrix, is balanced to render a scene 18% gray (for the new F5′s RGB meter, this doesn’t hold true). I’m sure you’ve heard that phrase before, but probably don’t understand what relevance it has to your photography. The most sited example to explain this is photographing a white wall; a camera meter will expose it to turn out 18% gray (a light gray tone). Most don’t bother to say that when photographing a black wall, the meter will try to turn it 18% gray as well, resulting in a flat black photograph.

If you looked at your camera meter while it’s pointed at the white wall, you’d see it isn’t giving you a reading equivalent to basic daylight. Rather, it’s probably reading f/22, equal to one stop underexposed. With a working knowledge and understanding of basic daylight, you would see the meter reading and understand you need to compensate by overexposing by one stop. This would make the white wall white.

This is a great theorem to have tucked away in your head, but all practicality precludes looking at the meter, comparing it to basic daylight and then compensating constantly when photographing wildlife. When that snow white Great Egret lands in dark blue water right in front of you, you might not have time to look at the meter and compare it to basic daylight. The same holds true if you’re photographing a brown bear fishing in the white water of a river. You must have a working set of compensation values in your head that you can instantly set your camera to without going through all the labor of calculating them mentally.

Experience is by far the best teacher for learning when and by how much to use exposure compensation. The drawback is all the great photographs lost in the process of building up your library of experiences. There is a way you can “jump start” your library of knowledge-using my infamous Teddy Bears.