Good focus of objects is a key element in producing a high quality digital photograph. You can achieve proper focus by two different methods, manual or automatic. We will concentrate on one method in particular that falls into the automatic focus category: combined auto focus.

It takes a combination of many optical parameters being set perfectly to create a high quality sharp and crisp photograph. One of the most vital optical parameters is focus. A photograph with objects out of focus appears blurry and lacks details and clarity. When objects are in focus the result is both sharp and crisp.

The focus can always be set manually by the photographer, but in most events the digital camera’s automatic focus feature will prove much faster and simpler. Digital cameras incorporate many various algorithms and methods to automatically calculate the right focus for the situation. Passive and active auto focus are two such algorithms that used together create a combined automatic focus system delivering excellent automatic focus. Passive auto focus systems use software that runs on the digital camera built-in computer.

Active auto focus systems use distance sensors that measure the distance from the camera to the objects in the scene. Usually the camera measures the distance to the object or objects around the center of the photo. By knowing that distance the camera can then set the camera lenses to achieve good focus. One of active auto focus biggest advantages is that it can work in complete darkness. On the other hand active focus can fail in problematic scenarios such as when objects emit certain energies (like infrared) are photographed or when surfaces in the scene absorb the energy used to measure the distance.

Active auto focus systems use distance sensors that calculate the distance from the camera to the objects in the scene. Typically the camera measures the distance to the object or group of objects nearest the center of the photograph. In calculating this distance the camera then programs the lens to achieve the best focus. One of the biggest advantages to active auto focus is its ability to function in total darkness. Active focus can fail though in challenging situations such as when objects that produce certain energies (like infrared) are photographed or when surfaces in the scenario absorb the energy that is used to calculate the distance.

Cameras that are equipped with combined auto focus systems pick the right system for the specific scene or cross check by using both systems at the same time. The photographer can also manually decide to use one of the two options. For example when shooting blue skies the camera can try to use the active system and measure the distance. Since the distance is infinite the camera can set the focus and skip the passive focus. In other cases when the distance is not infinite the camera can use the active system to put the lens in approximately the right position and then use the passive system for fine tuning. In dark scenarios the camera can opt to use the active system since the passive system will not work.

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