Photography

Focusing

Focusing is a process at which the camera lenses are moved until the subject becomes very clear and very sharp. Most cameras come with Auto-focus, Manual focus or both depending on the class of camera. Although most auto-focus systems in cameras most often perform a very good job in acquiring a sharp images, understanding a little bit about them and to learn their limitations would help you to be able to use them more effectively.

Auto Focus

In Auto Focus mode, the focus is locked when you half-press the shutter release button, often accompanied by a confirmation beep and a green indicator on the viewfinder. Focusing is accomplished by the camera based on the sharpnes and contrast of the most prominent, high-contrast image (usually vertical) inside the pre-defined focusing area. The camera often fails to auto-focus if: there are no prominent, high-contrast vertical image in the focusing area; the lighting is not sufficient; the subject is moving; or if there is too much bright light or reflections within the focusing area. In these cases it is important to learn other auto-focus settings to see which one will work better in a given scene.

Single Area focusing - The camera uses the center portion of the image (usually indicated by lines) to determine the distance of the subject and adjust the focusing accordingly.

Multiple Area focusing - Some cameras provide more than one focus area, some 3-point, 9-point, 11-point and other variations. With this mode, the camera chooses the most significant focusing areas and adjusts the focus position based on the image in the selected areas. They are often indicated by a change in color of the area's border.

Spot Focus - In this focusing mode, the camera uses a much smaller center area of the screen as a reference for the focusing position.

Face Detection - Also called Face-Priority AF, this mode has a special digital detection program that can distinguish facial details on the screen and accordingly adjusts the focus based on the position of this image. Newer models are even capable of multiple face detection which is useful for group photos.

Some cameras have controls to allow the user to customize the position of the focus area (single, multiple or spot) depending on the individual shooting style as some photographers tend to position their subjects off the center of the screen.

Manual Focus

When using manual focus the camera turns off all automatic focus systems. The user controls the focus by adjusting the focusing ring (SLR) or designated focus buttons. The focusing is based on the distance of the subject and is usually monitored by displaying the current focusing distance. The central portion of the View finder or monitor is usually magnified so the user can see better if the subject is already focused or not.

In some cameras, specially SLRs, special focusing screens with specific patterns are placed in the viewfinder to help determine the best focus. The patterns are usually made up of different masks that makes the images inside these patterns to blur or misalign if it is not properly focused.