In a previous article I questioned if the computer tech gadgetry found in modern digital SLRs would nudge us down one rung on the evolutionary ladder or at the very least, encourage laziness in our thought processes. To take it further I’m now wondering if new photographers are relying too heavily on the automation and intelligence found in today’s DSLR metering systems. Believe it or not, a good percentage of the time those sophisticated meters are wrong when computing an exposure. It’s just the nature of the beast.

DSLR meters measure luminance — the light reflected from the object you are photographing — not the amount of light falling on it. They calculate the exposure of the scene as an average tone of 18% gray. Thus, if your subject is predominantly black or predominantly white and fills up the composition, in both cases with a reflective type light meter, the subject will be exposed to appear gray. This type of meter only works correctly when your composition is a wide combination of tones and front lit… the situation in most compositions.

But what about the exceptions: the side lit or back lit scenes or the ones with the limited range of tones? This is where, as a photographer, you will need to out think your camera’s automation and where the Sunny F16 rule comes into play.

The Sunny F16 rule was used in the days when cameras didn’t have built-in light meters and a handheld one wasn’t available. The rule is as follows; when photographing a front lit subject of moderate size on a bright sunny day, set the aperture to f/16 and the shutter speed to the ISO (ASA in the past). In other words, if you are shooting at ISO 100, set the shutter speed to 1/100 (1/125 on a film camera). If you need a faster shutter speed, open up your aperture accordingly.

Of course if the subject is back lit, side lit, dark in tone, light in tone or if it is hazy or overcast one would need to compensate. For example, one needs to open up between 1 ½ to 2 stops if shooting in overcast conditions as there is less light.

In years past, most serious photographers understood the nature of light and used their meters as tools rather than as a crutch. So I propose a challenge. Since with digital, experimentation costs nothing but your time, go out and play around with the F16 rule. Try it on a sunny day and prove to yourself that it works. Experiment and discover what exposure compensations need to be made in varying lighting conditions with subjects of varying reflective properties. I guarantee you will walk away with a better understanding of exposure and that DSLR will become a tool under your creative control.

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