Choosing shutter, aperture, or manual mode on your digital SLR

The tips below are for shooting the best existing-light (no flash) photographs possible without relying on the camera to decide what's more important between shutter speed and aperture size. Understanding and properly selecting between these two modes will empower you to get the most out of your camera, because only you know what's important on the other side of the lens.

SLR cameras with shutter priority and aperture priority modes are set up to do a good job of getting the proper exposure by adjusting one variable. The photographer's job is to tell the camera whether to stick to a set shutter speed (shutter priority) or stick to a set aperture (aperture priority). In other words, when you shoot in shutter priority mode, the camera will automatically adjust the aperture size to get the proper exposure. And when you shoot in aperture priority mode, the camera will automatically adjust the shutter speed to get the proper exposure.

So before each shot, decide what YOUR priority is. Here are two scenarios:

Dog catching a ball in his mouth on a sunny day. You want to freeze the action just as the dog jumps into the air to catch the ball. You want to select a fast shutter speed, and you do not want the camera to automatically adjust the shutter speed by slowing down or speeding up the shutter for the proper exposure. You should shoot this photograph in shutter priority. So you select a shutter speed of 500 (1/500 of a second) and toss the ball to your dog. As the dog jumps up, you take the shot, and the camera automatically selects the perfect aperture to let in the perfect amount of light to give you a perfect exposure without letting the shutter stay open any longer or any shorter than 1/500 of a second.

Night softball game under the lights. You want a sharp photograph of the pitcher just as the ball leaves her hand and her ponytail arcs over her head. Here, the challenge is to get as much light through the lens in the shortest amount of time possible. You should shoot this photograph in aperture priority. Here's why: If you choose the smallest aperture number (for example f2.8), which is the largest aperture size (the biggest opening), then the camera will choose the proper shutter speed for the amount of light available. And because you selected the largest aperture, whatever shutter speed the camera chooses will be the fastest shutter speed possible for the lens you are using and the light you are shooting under.

What about manual mode? In manual mode, your camera's exposure meter will tell you when the camera thinks you chose the correct combination of shutter speed and aperture size for the available light. In manual mode, the photographer leaves the camera with nothing to think about. No ability to make adjustments when a cloud passes in front of the sun or the light slowly fades from the evening sky. You might have guessed that manual mode works best in unchanging light. You have guessed correctly.