When would I use exposure compensation?

Despite the high quality light meter in my camera, sometimes the images come out too dark or too light. Sometimes it is a matter of a subject that deviates from the 'norm' that my light meter has been designed to read. Other times, my images don't come out properly exposed because there is too great of a contrast range in my subject matter. And, occasionally my images don't come out well exposed, because the camera's choices are different from my artistic vision.

I'll explore these various situations with some examples.

In the example above, I was shooting on a heavily overcast morning. The sky was nearly white to my eye. The osprey was flying well over my head and was deeply shadowed underneath.

My camera's meter is designed to average subjects to an 18% (middle gray) value. I use the multi-pattern meter for greatest accuracy in the greatest number of situations, but sometimes it fails.

Since I photograph birds in flight regularly, I know the bright sky can present a problem for my camera's meter. To compensate, I ADD light to my exposure, either by increasing the aperture to a wider f-stop or increasing the shutter speed to a longer time. In the two compensated frames above, you can see the increase of brightness and detail with a + 2/3 f-stop and a + 1 and 1/3 f-stop increase in exposure.

In the example above, I made the choice to photograph in light that had too much contrast. The difference between the bright areas outside the window and the dark areas inside the house was too great to be captured in a single ambient light exposure. I could either a) add 2 stops of exposure (by adding time or widening the aperture) which would lighten the interior of the house or b) under expose by 1 stop to expose for the exterior.

There is one other option for the problem above - fill flash. If your subject is close enough to be illuminated with flash, you could under expose the image to get detail outdoors and add a flash to illuminate the interior.

Another reason to over or under expose an image is artistic vision. A couple of years ago, a friend and I were photographing at night in the Montlake neighborhood of Seattle. The lights from the street and the 520 freeway were bright, but the water of Lake Washington was black to our vision. I could see traces of shadows from the cottonwoods lining the lake. I decided to experiment with over exposing the image to see if I could see the trees reflected or shadowed in the lake. This is the result.

Of course, this is not at all what I saw at the time. Rather, it was what I envisioned the story to be. Using exposure compensation is one way of putting your own stamp on a story.

In this image, I underexposed to tell the story of the kayaker coming in at nightfall.

This image was overexposed to show the glow through the iris and to give the image an unworldly feel.