Changing Your Camera's Mind

Testing Your Camera

Thanks to digital, you can easily test the latitude of your camera and find out exactly how it will render tones. Follow this process to find out at exactly which point your camera begins to lose detail in the highlights and shadows. With this knowledge you will know what you're camera will do to a scene before you trip the shutter.

Find any colorless, single-toned subject; a white wall works well. You're going to take a series of photographs of it at several different exposures. Switch into manual mode, meter the wall, and photograph it just at the settings your camera recommends. That's you're middle gray exposure. Now take exposures as you lower the shutter speed by each setting (1/3 or 1/2 stop) up to 3 stops overexposed. Repeat the process in the other direction from your middle gray down to 3 stops underexposed.

You've just created a gray chart that will tell you at what point your camera renders pure whites and blacks. Looking at the histograms of these images will tell you how your camera treats various exposures.

First look for which exposure shows your highlights (whites) beginning to clip on the right side of the scale. It's usually between 2-3 stops overexposed, depending on your camera. If my whites begin to clip at 3 stops over, then whenever I'm using that camera I would never want my whites to be more than 3 stops higher that my meter's middle gray reading. Knowing this tells me how to meter my highlights, and they are the most important tones to control in exposure.

Another thing to notice from the test is how your shadows react differently than your highlights. Look at your histograms in the underexposed frames. It takes the shadow frames reach a true black, as opposed to the highlights which race to the clipping point. Highlights lose detail quickly. With some cameras the highlights begin to lose detail only two stops over middle gray, while the shadows retain detail as much as 3.5 stops under.

Knowing your camera's limits will help you push things to the edge without falling off.

Exposure Compensation

There are times when it's a good idea to photograph in an auto-exposure mode. I'm thinking of situations where the lighting is changing quickly and you're trying to capture moments. In such situations you don't always have time to check your exposure. If you have to shoot in auto-exposure mode, learn to use your camera's exposure compensation setting.

Exposure compensation lets you tell your camera to under or overexpose by an amount you set. For example, if you are taking pictures on a family ski outing, the bright snow is going to throw off your meter. You can compensate for this by setting your exposure compensation to +1.5 stops, which will cause your camera to overexpose by that amount and keep the snow white. (Of course, make some test frames before you take my word for it! I don't want to be responsible for destroying the memories of your family ski trip.)

If you're photographing someone in front of a black wall, you can compensate by setting your exposure compensation to -1 or more stops, so that it underexposes. By making a few exposures and checking them on your LCD screen, you can narrow in on the exact setting for your situation.

WARNING!!! Don't forget to turn off exposure compensation when you no longer need it. As long as it's active, every photograph you take will be over or underexposed to the level you set. Most cameras have an indicator to remind you that exposure compensation is set, but I guarantee that you will forget that it's on from time to time.


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