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 How does auto-focus work?

Most of us put it to use every time we click on the shutter button. Practically all modern cameras include some sort of a car focus system. As a result of the auto focus system we could enjoy an easier photography experience and can concentrate on composing the proper photo and capturing as soon as rather than on manually setting the focus.tập trung cao độ

Automatic focus though has its limitations. For example sometimes one might want to produce photos which are a bit fuzzy as an imaginative expression. Also the auto focus implementation has its limitations and in certain scenarios it would fail. One example is using a high end SLR camera with an inactive auto focus system to have a picture of blue skies. Generally the camera will move its motor back and forth and could eventually stop trying and don't focus.

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

Passive auto focus:

Passive auto focus can be perceived as imitating how exactly we set the focus manually. The camera defines a number of regions in the picture (usually they're 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 posture where in fact the Focus Level could be the highest. For that time if the Focus Level is above a predefined threshold the camera would define this region of the photo as being in focus.

The Focus Level can be calculated in lots of ways. The normal attribute of calculations is working out how much Contrast will there be in the photo. While not in the scope of this information one method to calculate this type of number is by running the photo through a high frequency filter - that is on the basis of the proven fact that high contrast is related to high frequencies.

Active auto focus:

Active auto focus works by measuring the length between the camera and the thing in the picture. Technically if you knew the precise distance to the thing you are taking a picture of you may set the lens to the precise focus position. The active focus system shoots a beam of invisible light, usually infrared, at the thing at the center of the picture and measures the length to that object. Centered on that distance the focus is set.

Combined auto focus:

Some high end cameras combine both systems. The camera will pick the proper system for the precise scenario or will cross check and use both at the exact same time. The photographer may also decide manually to make use of among the two options. For example when shooting blue skies the camera can attempt to utilize the active system and measure the distance. Since the length is infinite the camera can set the focus and skip the passive focus. In other cases once the distance isn't infinite the camera can utilize the active system to put the lens in approximately the proper position and then utilize the passive system for fine tuning. In dark scenarios the camera can prefer to utilize the active system considering that the passive one will not work.

So just why doesn't the auto focus work all the time?

Even with the electronics and computing power in the camera there will always be scenarios where in fact the camera auto focus fails. Failure can be once the camera can't focus and the picture is fuzzy or sometimes once the picture is clearly in focus however the camera "thinks" that it's not.

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

- Taking low light pictures: The passive auto focus system needs to "see" the picture in order to work and in low light scenarios this isn't possible. Some systems use a series of flashes to overcome this limitation but this solution fails many times. An active system can measure the distance to the thing such scenarios but will fail if the thing isn't in the center of the picture or if there are certainly a few objects at different distances.

- Active systems can fail with objects that have a tendency to absorb the infrared beam they're using. Some materials absorb infrared beams and may cause the active system to measure the wrong distance. In certain scenarios other infrared sources such as for instance candles and open flame fires can render the active system useless.

- Low contrast objects such as for instance white walls or blue skies. The passive auto focus depends on the fact that the Focus Level changes significantly when moving the lens back and forth. This allows the camera to settle on the proper focus position. The Focus Amount of low contrast objects doesn't change much and fails the passive system.

Knowing how the auto focus system works helps a photographer realize why sometimes the camera can't focus. In such scenarios the photographer can look for other solutions. Sometimes the photographer will need to utilize the manual focustập trung cao độ. In other cases emphasizing another object in the picture that is in the exact same distance but easier to focus on and locking the focus on that object will solve the problem.