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Focus
With the auto focus mode available on most digital cameras the process of creating sharp images is hugely simplified but that doesn’t mean you will always get it right. Depressing the shutter button halfway, while training the lens on the subject, will allow the camera to set focus. Most camera’s have a small rectangular image visible centrally on the viewfinder or on the LCD screen to denote the point where focus will be concentrated.
A photograph where the entire scene is in focus is usually common in landscape images. Using the landscape scene mode on your camera will lock the focus at infinity, which means that the camera will attempt to ensure every part of the image is in focus, however this type of focus is not suitable for other photographic subjects.
It is essential that the main object of interest is in focus but it is generally more critical that a particular part of the subject be in focus. The general tendency of a snapshot taker is to focus on the middle part of the face, which is usually the nose, but focusing on the eyes will create more impact and ensure they remain clear and sharp.
Choosing an area of selective focus is a technique known as creating a Depth of Field. The depth of field is the area of sharpest focus around the subject of interest. A large depth of field means the most of the image is in focus, a small depth of field means that most of the image will be out of focus except for a specific area. Two manual controls allow you to control the depth of field. The focal length of the lens and the aperture, measured in f-stops. The longer the focal length and the wider the aperture, the smaller the depth of field.
Aperture works similarly to the way in which your eye focuses – by dilating and contracting to change the amount of light taken in. Larger apertures such as f2 have a selective depth of field while smaller apertures like f16 will result in most of the image being in focus.
Depth of field is very effective in portrait shots where the person is in sharp focus but the background is sharp and blurry. It is also effective to emphasize particular detail in a scene.
Controlling depth of field is a skill that requires practice. In high end digital cameras you may find you have a DOF preview button. This will allow you to view the depth of field before taking the photograph. Even if your camera doesn’t have the ability to change the aperture, automatic modes such as landscape, portrait and macro work by changing the aperture to pre programmed settings. Landscape mode puts the entire scene in focus, Macro mode narrows the depth of field dramatically, while the portrait mode reduces the depth of field, keeping the center of the image in focus while softening the background.
DC Mag UK Master Your Camera: Depth of Field
shortcourses.com Digital Photography Sharpness
Digihelp.com <a href="http://www.digicamhelp.com/digital-camera-focus-modes/" digital camera focus modes
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