In the 2nd article in a series explaining DSLR camera settings, we'll cover what the letter "A" means on your camera setting dial. To be concise, we'll use Wikipedia's explanation...
Aperture priority, set by dialing to the letter(s) A or Av (for Aperture value on Canon DSLRs) on a camera mode dial, is a setting that allows the user to choose a specific aperture value while the camera selects a shutter speed to match. The camera will ensure proper exposure. This is different from manual mode, where the user must decide both values, shutter priority where the user picks a shutter speed with the camera selecting the aperture to match, or program mode where the camera selects both.
The main purpose of using aperture-priority mode is to control the depth of field. Aperture priority is useful in landscape photography, where a narrow aperture is necessary if objects in foreground, middle distance, and background are all to be rendered crisply, while shutter speed is often immaterial. It also finds use in portrait photography, where a wide aperture is desired to throw the background out of focus and make it less distracting.
Another common use of aperture priority mode is to suggest how the camera should determine a shutter speed, without risking a poor exposure. In landscape photography, a user would select a small aperture when photographing a waterfall, hoping to allow the water to blur through the frame. When shooting a portrait in dim lighting, the photographer might choose to open the lens to its maximum aperture in hopes of getting enough light for a good exposure.
In addition, aperture priority mode allows the photographer to force the camera to operate the lens at its optimum apertures within its aperture range for a given focal length of the lens. Commonly, lenses provide greatest resolving power with relatively medium-sized apertures.
Yup, that was concise, but I'm sure you'd like like some visual examples to help you out, so click here for a great article from wikihow.com that further explains this great mode to use on your DSLR. If you need some more help, join us for our monthly "Digital SLR Basics" class on Thursday (3/14) at 6:30 PM. Our classes have been fun, informative and very well attended this year and we're sure they will help you use your DSLR to it's full potential.
BTW, there are some great instant rebate savings from Canon and some new cameras from Nikon that we'll fill you in on later this week!