For the first six months of my relationship with my Canon 40D SLR, I did not know a quick way to correct exposure. I would take a photo that was too dark or too light, and I would start fumbling around with the f-stop and/or shutter speed to correct it and by that time my subject was in the kitchen eating lunch. I'd shrug my shoulders and set my camera down.
Then! I discovered the wonderful little secret that is exposure compensation. This handy little feature has made picture-taking a million times easier. Fumbling is a thing of the past for me, thankfully, because I don't like to fumble. Now when I take a photo that is too light or dark, I can easily make a correction in a matter of seconds. My subject doesn't have time to run away from me!
What is exposure compensation? Exposure compensation allows you to easily control the amount of light that enters the camera. It overrides the exposure setting that has automatically been chosen by the camera. Sometimes a camera's auto adjustments are not entirely accurate (or just not to your liking), so you must do a bit of your own adjusting.
Where on my camera can I find exposure compensation? First of all, exposure compensation can only be used in the following modes: Program (P), Aperture Priority (Av or A), Shutter Priority (Tv on Canon; S on Nikon) and Manual (M).
While in one of the above modes, look for a button on your camera that resembles the below image with a +/- symbol. It can be found either on the top or toward the top back side of your camera, depending on the brand and model.
First, press the shutter button half way down and release. Then hold down the +/- button while simultaneously turning the main dial, which can usually be found on the top of your camera near the shutter button. Turning the dial to the right will allow more light into the camera and will lighten your image. Turning the dial to the left will allow less light into the camera and will darken your image. (This applies to Canon SLR cameras. For Nikon SLRs, do the exact opposite. Turn the dial to the right to darken and to the left to lighten.)
On my Canon 40D, I make exposure compensation adjustments by holding my shutter button half-way down and simultaneously turning the back dial on my camera, as long as the back dial is active (turn power button past ON and to the line that points up toward the back dial).
The exposure adjustments you make will be visible on an icon on the top status panel or on the back LCD display (depending on the camera) that looks something like this:
Most cameras adjust exposure in third-step increments, and some in half-step increments. On my Canon 40D, if I turn my dial three clicks to the left, this is what I will see:
This shows that I have lowered (-) the exposure by 1 EV (Exposure Value) step.
And if I want to increase (+) the exposure by 1 EV step, I turn my dial three clicks to the right and this will appear on my status panel:
Here are a few examples of photos taken underexposed (-1 EV), autoexposed (0 EV) and overexposed (+1 EV):
When should I use exposure compensation? If there is a lack of natural or quality light, this would be a good time to experiment with increasing the exposure. I use exposure compensation on my camera a lot for this purpose. I take many photographs in and around our home, which happens to have very poor natural lighting, so I overexpose a good chunk of the photos I take. 95% of the food-related photos you see on this blog are overexposed, and a lot of my portraits are, as well.
Another good time to adjust a camera's exposure is if you are shooting a subject that is either backlit or that has a very bright background. The light from the background can confuse the camera and cause it to adjust its exposure according to that, instead of the foreground in which your subject is located. In this scenario, overexposing your photograph will help to lighten the subject.
If you are shooting a subject that has a strong front light that is causing some of the detail in the subject to be washed out (lost), underexposing the photo will decrease the amount of light glaring off your subject which will help to preserve some of the detail.
For high-contrast settings, it is beneficial to underexpose the photo so that the brightest parts do not become washed out. It is much easier to pull detail from dark areas than it is from washed out areas.
Get to know your camera's exposure compensation! It will save you a headache or two and you will be happier with the photos you take.