How can auto-focus work?

Many of us put it to use every time we go through the shutter button. Practically all modern cameras include some type of an automobile focus system. Because of the auto focus system we could enjoy a simpler photography experience and can concentrate on composing the right photo and capturing the moment as opposed to on manually setting the focus tập trung cao độ.

Automatic focus though has its limitations. Like sometimes one should produce photos which are a bit fuzzy as a creative expression. Also the auto focus implementation has its limitations and in some scenarios it will fail. One of these is using a top end SLR camera with a passive auto focus system to have a picture of blue skies. In most cases the camera will move its motor back and forth and will eventually quit and neglect to focus.

To better utilize the auto focus system it would help to know high it really works. Although implementations may vary we could divide them into two categories: passive and active. Most pocket cameras utilize the cheaper passive method while top quality professional cameras use either the active or a variety of both.

Passive auto focus:

Passive auto focus could be perceived as imitating how exactly we set the focus manually. The camera defines a number of regions in the picture (usually they are marked as rectangles on the viewfinder or the LCD). The camera then analyzes the picture seen through those regions and calculates a Focus Level number. The camera then tries to go its lenses back and forth as it recalculates the Focus Level. The camera looks for a situation where in actuality the Focus Level is the highest. For the period if the Focus Level is above a predefined threshold the camera would define this region of the photo to be in focus.

The Focus Level could be calculated in lots of ways. The most popular attribute of calculations is finding out how much Contrast is there in the photo. But not in the scope of this information one method to calculate this type of number is by running the photo by way of a high frequency filter - this really is based on the undeniable fact that high contrast is connected with high frequencies.

Active auto focus:

Active auto focus functions by measuring the length involving the camera and the thing in the picture. Technically if you knew the exact distance to the thing you are having a picture of you may set the lens to the exact focus position. The active focus system shoots a beam of invisible light, usually infrared, at the thing at the biggest market of the picture and measures the length compared to that object. Predicated on that distance the focus is set.

Combined auto focus:

Some top quality cameras combine both systems. The camera will pick the right system for the specific scenario or will cross check and use both at the same time. The photographer also can decide manually to use one of the two options. Like when shooting blue skies the camera can make an effort to utilize the active system and assess the distance. Since the length 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 utilize the active system to put the lens in approximately the right position and then utilize the passive system for fine tuning. In dark scenarios the camera can choose to utilize the active system since the passive one won't work.

Why doesn't the auto focus work all the time?

Even with the electronics and computing power in the camera there can be scenarios where in actuality the camera auto focus fails. Failure could be when the camera can not focus and the picture is fuzzy or sometimes when the picture is obviously in focus however the camera "thinks" that it is not.

The causes of such cases? The list is long but listed below are just a couple examples:

- Taking low light pictures: The passive auto focus system must "see" the picture to be able to work and in low light scenarios this is not possible. Some systems use a series of flashes to overcome this limitation but this solution fails many times. An energetic system can assess the distance to the thing such scenarios but will fail if the thing is not in the biggest market of the picture or if there are a few objects at different distances.

- Active systems can fail with objects that tend to absorb the infrared beam they are using. Some materials absorb infrared beams and can cause the active system to measure the wrong distance. In a few scenarios other infrared sources such as candles and open flame fires can render the active system useless.

- Low contrast objects such as white walls or blue skies. The passive auto focus relies on the fact that the Focus Level changes significantly when moving the lens back and forth. This enables the camera to stay on the right focus position. The Focus Degree of low contrast objects does not change much and fails the passive system tập trung cao độ.

Knowing how a auto focus system works helps a photographer understand why sometimes the camera can not focus. In such scenarios the photographer will look for other solutions. Sometimes the photographer must utilize the manual focus. In other cases concentrating on another object in the picture that's in the same distance but easier to target on and locking the give attention to that object will solve the problem.