Aperture Priority Mode - Better Photos... Now!

While you can control the overall sharpness of your subject and photo by adjusting the shutter speed of your DSLR, you can control how much of your photo is in focus by adjusting the aperture. Most DSLRs have an aperture priority setting (usually called A or AV) that lets you select a constant aperture for your camera, while your camera adjusts the shutter speed to give you the correct exposure.

By adjusting the aperture of your camera, you can decide if you just want the subject to be in focus with an out of focus background, or if you'd like the subject and background to be in focus. For most portraits, a lower aperture setting is usually more desirable. How low you should set your aperture depends on your lens and your subject.

Let's say you've got a 50mm lens with an aperture of f/1.8. If you're just taking a photo of one person, you can use an aperture setting of f/2.8 which will give you a nice blurry background but a sharply focused subject. If, on the other hand, you're photographing 2 or 3 people, you might want to use an aperture of f/4 or f/5.6, which will give you a wider plane of focus and should ensure that no one is out of focus.

If you're using the same 50mm f/1.8 lens and are shooting a landscape instead of people, you'll probably want to make sure that everything in the photograph is in focus. To do this, you'll want to choose the highest aperture available on your lens, probably f/16 for this particular lens.

For either of these examples, once you choose the aperture you want to shoot at, your camera will choose a shutter speed that will give you the correct exposure. Be aware, though, that when shooting at your highest and lowest apertures, you may approach shutter speed limitations. For example, if you decide to shoot at f/1.8 in full sun, your camera might not be able to set a shutter speed high enough for a correct exposure and you'll end up with an overexposed image. If you decide to shoot a sunset at f/16, your camera might leave your shutter open for too long to shoot without a tripod. Imagine if you set your aperture, started shooting a bunch of photos, then later discovered that every photo was overexposed or blurry!

Shot at f/8 with a 12mm lens - notice how everything is in focus

Shot at f/1.4 with a 50mm lens - Notice how even her ears are out of focus.
 That's a brick wall  about 10 feet behind her.

Read all of my DSLR tips here.