Even if you don’t use a handheld light meter, it’s still important to know if your camera’s built-in meter is measuring light correctly and delivering the best exposures possible. Remember, the goal of a calibrated meter is to produce images that are so well exposed that no tweaking or processing is necessary before going straight to proofs.

Fortunately, knowing how your meter is performing (and fixing it if it’s not quite right), is really easy.

You’ll need a manufactured neutral gray target. The best I’ve found are collapsible and sold (in various sizes) by Lastolite (the EZBalance, www.lastolite.com) and BalanceSmarter (www.balancesmarter.com). The only difference between the two is that the BalanceSmarter product has a target printed on both the white and gray sides so your auto focus can easily lock on either. At last look, Lastolite’s product target was only printed on the gray side. That’s fine for this test because gray will produce an easier to read result.

Begin by setting the target against a wall or attaching it to a light stand, making certain the light falling on it looks as even as possible. Mounting your camera to a tripod might make this easier but is not necessary. It won’t matter if the final image shows motion blur, we’re only interested in the overall exposure.

With the camera set to either Aperture Priority (Av) or Shutter Priority (Tv), and without any supplementary Exposure Compensation, fill the frame with the target and make an exposure.

Select the image and find the version of the Info image that shows the Histogram. The histogram is merely a representation of the spread of pixels over the various tones that make up an image but it can also indicate over or under exposure. Ideally, when you look at the histogram of a photo of a gray target, you’ll see the primary spike of tones dead center in the graph.

Often, the histogram will be skewed to left or right of center. Left of center means the images will be underexposed, right of center indicates overexposure. This is just a guess because no manufacturer would ever admit it, but from what I’ve seen in the numerous cameras I’ve purchased, cameras exhibiting slight underexposure are more apt to pass Quality Control because slight underexposure is easier to correct. Should your spike not be centered, here’s what to do:

If the spike is left of center, use Exposure Compensation and move the compensation indicator one mark to the right. Take another picture and evaluate the histogram. If it’s still left of center, try moving the indicator one more mark to the right, until the spike is as close to center as possible. Do this in reverse if the spike is right of center. The closer you can get to center, the better your automatic exposures will be. When you find the magic spot, leave it there (this camera required a plus exposure of two clicks right, or +2/3 stop to center the spike), and shoot automatic mode images with confidence. For many cameras, Exposure Compensation also works in Program mode, although that mode is very imprecise compared to Av or Tv.

It may be somewhat hard to believe that your precision camera would be off, but they do tend to drift, and for many reasons. It’s a good idea to repeat this test often.