It’s All About the Light

(This article appeared in full on Rob’s website Strange, Geometrical Hinges and is represented here as part of the CMPG library.)

Here’s a startling revelation – photography is about light. (Surprise!) Not just how it falls on the subject and its aesthetic quality, but fundamentally how much of it you’ve got. Proper technique with regard to exposure comes down to making sure that enough light comes through the lens just long enough for the film or image sensor to record it. Ideally, you want to see the details in the darker areas of your photo without washing out the highlights. This balancing act is the key to good photography.

As cameras have grown more technologically advanced, you’d think that features like spot, weighted, and multi-segment metering would eliminate the guesswork for a photographer. In many cases, this is true. However, while they strive to achieve the “perfect exposure” for any average scene, they’re quite easily fooled. Whenever you depart too much from an “average” scene, you’re working outside the envelope of the camera’s through-the-lens (TTL) meter and exposure computer. You’ve embarked on a quest through unfamiliar territory in search of proper exposure.



In the image at the upper left, there are a number of challenges to this goal. First, the subject is very pale (and I don’t think a tanning booth will help her). Second, there needs to be separation between the subject and the background – you don’t want them to be of equal brightness or else the subject loses impact. Finally, the lighting is mostly directional – there’s three times as much light coming from the left of frame (1500W of flood), as opposed to the fill lighting on the right (500W off a gold-tone reflector).

In-camera meters take light readings through the lens. They depend on reflected light from the subject, and use it to create a balanced image. The accepted rule-of-thumb is that the average scene reflects 18% of the light striking it, and this is what the camera’s meter uses to calculate proper exposure. However, what happens when the shot contains subjects of widely varying reflectivity, or when there’s a large amount of contrast between subject and background?

In the example above, metering across the whole scene would create an average image – properly exposed all the way around. However, because of the compromises made by the meter to achieve this balance, you’d end up with poor subject/background contrast. Meter off the pale subject, and the background is underexposed. Meter off the background and the subject is overexposed and washed out. What to do? The photo below (cropped from 3:2 aspect frame) illustrates this principle – it was taken using multi-segment metering, and shows how the camera tries to achieve balance throughout the frame to the detriment of the overall picture.

So how do you you fix this? The obvious answer is by bracketing your exposures – taking a shot at the camera’s metered reading, and then a few more slightly over- and under-exposed. Then, pick the best image. The problem is that this takes extra time, and in the case of classic photography, extra film. If you’re not in a hurry and don’t care about wasting a few frames, this is a method worth trying. Some more advanced, automated camera bodies will even take a 3-frame bracketed series with each push of the shutter button.

Suppose, though, that you want to get it right the first time, or at least have a darned good chance of accomplishing your exposure balancing act. The best tool that requires the least amount of guesswork is the hand-held exposure meter. These are the little boxes with a white ball on the end that you’ll see studio photographers holding in front of their subjects. They don’t measure reflected light like a camera does. They measure incident light – the amount of light that’s falling on the subject before it’s reflected back to the camera. Thus, they’re not affected by the color or reflective qualities of the subject and background.

To use one of these meters, one stands at the subject’s position and points the ball of the meter at the camera lens (usually from face-level, if shooting portraits). A reading is taken, and the corresponding shutter speed and aperture are manually set on the camera. The photo below was taken with the same digital camera, from the same position, with identical lighting as that above. The only difference is that the metering was done off-camera with an incident meter.

Notice the better contrast separation between subject and background, and the more pleasing quality of the light. The in-camera TTL meter, due to the almost-white surface of the subject, was fooled into underexposing the first photo by a about 2/3 of a stop. By using the incident meter, which is unaffected by the bright subject, and setting the aperture and shutter speed manually, we were able to achieve a much better image.

Incident meters of decent quality run about $70 at a well-stocked photo store. Even if you use a digital camera, they are a worthwhile investment, especially if you do any serious shooting in studio with artificial light. While using a light meter and manually setting parameters may seem “old fashioned” in this high-tech era, sometimes it pays to forgo the automation and become a hands-on photographer. Happy shooting!