Photo Exposure 101

If you've ever wondered what makes up a picture, then find out all you need to know about photo exposure. Photo exposure is important because you need to learn how to adjust your exposure if you want to shoot great photographs.

What is Exposure?

You can think of exposure as the amount of time that a digital sensor or a piece of film has to absorb light. A long exposure will result in a washed out bright image, while a short exposure time will give you a dark or muddy looking image. In almost every situation, you can over or under expose a picture depending upon the amount of light that's available.

What Does Exposure Do?

Exposure affects quite a few elements of your final image. Most obviously, the length of a photograph's exposure will control how dark or light it turns out. In dark lighting situations, a longer exposure will be required to allow the camera more time to "see" the subject, whereas in bright lighting situations a fast exposure will prevent the film from being blinded. Exposure also has an impact on how blurry or sharp moving objects appear in an image. For example if you were to take a picture of a basketball player making a dunk, a fast exposure would give you a clear frozen image of the player making his shot. Don't worry about a little motion blur, but if the exposure isn't fast enough it's likely that the action shot will turn out bad.

And lastly, exposure also controls the depth of field. Depth of field determines how fast the background loses sharpness and how much of the picture is clearly focused. When our exposure time is short, your depth of field will be more shallow because your camera doesn't have as much time to absorb data. If you want a larger depth of field, you can always increase the exposure time but just remember that this may cause motion blur in your image.

How to Work with Exposure

By adjusting the shutter speed, you can control the exposure of any picture. Fast shutter speeds give you a very short exposure time whereas slow shutter speeds give you longer exposure times. Depending upon what you're trying to accomplish with your image and the type of available lighting will determine if you need to have a long or short exposure. For example, pretend you're taking a picture of a kid riding a bike. If you have a slower shutter speed or a long exposure, you will get motion blur as the child rides by on his bike but you may still see the background in focus. If you use a short exposure (or a high shutter speed) you will freeze the child in motion while blurring out the majority of the background.

In this particular case, a shorter exposure may be your best option if the light is so intense that a low shutter speed will over-expose your image. If you need to change your exposure you can always reduce the amount of light entering your lens by changing the f stop or aperture but sometimes your exposure will need to be determined by the quality of your light.

Dealing with exposure is just one of the many ways that you can control the final output of your images beyond framing a subject and hitting the shutter button. When you can think about what your shutter speed means, you will be able to purposefully change the amount of motion blur and depth in every photograph you take. And fortunately with SLRs these days you can select your shutter speed and the camera will figure out everything else.