Learn Digital Photography Now... Digital Cameras and Combined Auto Focus

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.

High quality sharp and crisp digital photos are a result of many optical parameters that need to be set right. One of the most important optical parameters is focus. When objects in a digital photo are out of focus they look blurry and are missing details and clarity. When objects are in focus they look sharp and crisp.

While the focus can be manually set by the photographer in most cases using the digital camera's automatic focus feature is much easier and faster. There are many different algorithms and methods that digital cameras use in order to automatically determine the right focus for a specific scenario. Such algorithms include passive and active auto focus. One type of combined automatic focus system uses these two algorithms to delivery superior automatic focus.

The camera performs image processing algorithms to establish a Focus Level number. This number is reached through a process much too detailed and difficult to tackle in this article. Let's just say that the camera can determine how good the focus is and then find the best focus for the scene. There are the occasions where the passive auto focus is restricted or does not work at all. It does not function well in low lighting conditions and does not work at all in dark scenarios. It is also difficult to focus on low contrast objects such as solid surfaces or walls.

Passive auto focus systems use software that runs on the digital camera built-in computer. The camera executes such image processing algorithms to determine a Focus Level number. The exact way in which such a number is calculated is out of the scope of this article. Suffice is to say that the camera uses some image processing algorithms with which it can calculate how good the focus is. Using these algorithms the camera can find the best focus for the scene. In some scenes the passive auto focus is limited or not functional at all. It does not work well in poor lighting conditions and does not work at all in dark scenes. It is also hard to focus on low contrast objects such as walls or solid surfaces.

Those cameras that are outfitted with combined auto focus systems have the ability to use the right system for the specific situation or cross check by using both systems at the same time. Of course, the photographer can also manually choose which option if they so desire. As an example, when shooting blue skies the camera can try to use the active system and calculate the distance. Since the distance is endless the camera can set the focus and skip the passive focus. In other cases when the distance is not endless the camera can use the active system to put the lens in about the right position and then use the passive system for fine tuning. In dark circumstances the camera can choose to use the active system given that the passive system will not work.

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