Controlling the depth-of-field in your shots is one of the most important aspects of creative photography. It’s quick and easy to do, and mastering the process will give you a real ‘eureka’ moment on your path to better pics!
Shoot at your minimum aperture
Now rotate the command dial until you’ve set the highest f/number. This is the minimum aperture value and is again governed by the lens you’re using. On most lenses this will be f/22, but it could vary between f/16 and f/64 depending on what optic you have fitted, and how far zoomed in you are. Check the shutter speed in the view finder, and you’ll see that it’s much slower than your previous shot. This is a result of the aperture being closed to let the minimum amount of light through. The image in the viewfi nder won’t change, but take another shot, and when you check the screen you’ll see that the zone of sharpness now extends much deeper into the scene, despite the lens being focused in exactly the same place. Once you’ve run this easy exercise, think about the aperture value you use on every shot you take. Decide what your shot is about, and what you’re trying to express. This will help you choose between a large aperture that isolates the point of focus in a shallow band of sharpness, or a small aperture that gives great a great depth-of-field through the entire scene.
Set up your shot
Find a subject reasonably close to the camera, and make sure there’s a distance of at least a few metres between it and your background. With your camera on a tripod, compose your shot and focus on the subject by placing the active AF point over it and half pressing the shutter. Once you’ve established focus, switch the focusing selector switch to MF to lock the focusing distance. This will prevent the focus from changing, so your results will be determined by the aperture setting alone. Through the view finder, you’ll see the pic at maximum aperture, so your background will look blurred.
Shoot at your maximum aperture
Now set your main mode dial to Aperture priority (A or Av). Rotate your command dial until you’ve set the largest aperture available. This is governed by the lens you have attached, and will be the lowest f/number. On an 18-55mm kit lens, this will be between f/3.5 and f/5.6 depending on how far zoomed-in you are. Once you’ve done this, take the shot. Check the screen and you’ll see the image appears exactly the same as in the view finder, with a sharp subject and a fuzzy, out-of-focus background. Your shutter speed will vary, but make a mental note of it.