January 4, 2013

Focusing Tips for Digital SLR Cameras

Automatic focus on digital SLR cameras is a separate function from automatic exposure. Automatic or manual focus is typically a control on the lens itself but sometimes a control on the camera body. Usually there is a switch labeled “AF” for automatic focus and ”MF” for manual focus.

If you set the switch to AF, auto focus, you press the shutter button halfway down to ask the camera to focus. When it achieves focus, one or more of the squares in the viewfinder light up to indicate where in the scene the camera chose to focus. You also see a confirmation light, usually a solid green dot, inside the viewfinder along the bottom to indicate the camera is able to achieve focus. Then you can press the shutter button the rest of the way to take the photo.

Single vs. Continuous Auto Focus
Some cameras have multiple styles of auto focus. Single or one-shot auto focus sets the focus distance when you press the shutter button halfway. This distance doesn't change, even if the subject moves closer or farther from the camera. This type of auto focus is best for stationary subjects like landscapes or flowers.

Using single or one-shot auto focus can create blurry photos of moving subjects. Instead try your camera's continuous or servo auto focus choice. This can be a button near where the lens attaches to the camera or a menu choice. (Consult the camera manual for directions.)

Continuous auto focus locks focus when you press the shutter button halfway. If the subject moves, the auto focus tracks the movement, constantly updating or "predicting" the distance the subject will be from the camera when you press the shutter button all the way to take the picture. This type of auto focus works best for subjects moving toward or away from the camera, such as a child on a swing photographed from the front.

Using continuous autofocus


Some SLR cameras now provide Face Detection auto focus and Live View focusing. Check your camera manual for information on these styles of focus.

Changing the Active Auto Focus Point
Automatic focus is often programmed to focus on the object closest to the camera. There are several focus points or areas (little squares or brackets visible in the viewfinder) that the camera checks to determine where in the scene the closest object is. The camera may select a different object than the one on which you want it to focus. If you are trying to control where the camera focuses, this can be frustrating.

You can change the way the camera uses the auto focus points or areas. Instead of leaving all the focus points active, you can change the camera setting so that it uses only the center auto focus point or area (square). (Refer to your camera manual for instructions.) This way you can be sure the camera is focusing on the object you select instead of one the camera chooses.

After setting only one auto focus point or area to be active, you can reposition the active point to the right, left, top or bottom of the viewfinder instead of the center. This allows you to auto focus on a subject off to one side without having to change your composition.

When Auto Focus Doesn't Work
Automatic focus does not work in all situations. If you point the camera at a blank wall or a plain sky, the lens may go in and out as it seeks for something to focus on. Because there is not enough detail, the camera can’t focus. The confirmation dot in the viewfinder blinks and the camera may not let you take a picture.

To solve this problem, point the camera at something the same distance away that does have detail, for example, a break or corner in the wall or the edge of a cloud or the horizon. Press the shutter button halfway down to set the focus. Keeping your finger on the button, shift the camera back to your original scene and press the button the rest of the way. This technique is called focus lock.

Automatic focus may also choose to focus on something other than what you intended. This happens most frequently when there are objects between the camera and your subject, for instance, the bars or fence of a cage instead of the animal behind it, nearby grass or twigs instead of the animal or horizon, or glass instead of what you see through it. In this situation, you may need to change to manual focus in order to be able to focus where you want.

Using Manual Focus
To use manual focus, first set the focus switch to MF, manual focus, and then turn the focus ring on the lens. The focus ring has a different style of ribbing and is a separate ring from the zoom ring. As you turn the focus ring, hold down the shutter button halfway and check the focus visually through the viewfinder. When you see the focus confirmation dot appear, your subject is in focus and you can make the shot.

Give these focus techniques a try with your camera and see how you can improve the number of sharp pictures you take!