tập trung cao độ

[Jane Maria]

So how exactly does auto-focus work?

All of us use it every time we click the shutter button. Practically all modern cameras include some kind of an automobile focus system. Thanks to the auto focus system we are able to enjoy an easier photography experience and can pay attention to composing the best photo and capturing as soon as as opposed to on manually setting the focus tập trung cao độ.

Automatic focus though has its limitations. Like sometimes one may want to produce photos which certainly are a bit fuzzy as an imaginative expression. Also the auto focus implementation has its limitations and in some scenarios it might fail. One example is using a high end SLR camera with a passive auto focus system to take a picture of blue skies. Generally the camera will move its motor back and forth and could eventually give up and neglect to focus.

To raised utilize the auto focus system it'd help to comprehend high it actually works. Although implementations may differ we are able to divide all of 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 mix of both.

Passive auto focus:

Passive auto focus could be perceived as imitating exactly how we set the focus manually. The camera defines one or more 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 since it recalculates the Focus Level. The camera looks for a situation where the Focus Level is the highest. For that point 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 could be calculated in several ways. The most popular attribute of calculations is working out just how much Contrast can there be in the photo. But not in the scope of this short article one way to calculate such a number is by running the photo through a high frequency filter - this is based on the undeniable 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 object in the picture. Technically in the event that you knew the actual distance to the object you are taking a picture of you might set the lens to the actual focus position. The active focus system shoots a beam of invisible light, usually infrared, at the object at the center 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 best system for the precise scenario or will cross check and use both at the exact same time. The photographer also can decide manually to utilize among the two options. Like when shooting blue skies the camera can try to utilize the active system and measure the distance. Since the length is infinite the camera can set the focus and miss 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 best position and then utilize the passive system for fine tuning. In dark scenarios the camera can opt to utilize the active system since the passive one won't work.

Why doesn't the auto focus work constantly?

Even with all the current electronics and computing power in the camera there can be scenarios where the camera auto focus fails. Failure could 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.

What can cause such cases? The list is long but here are just a few 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 isn't possible. Some systems use some flashes to overcome this limitation but this solution fails many times. An active system can measure the distance to the object in such scenarios but will fail if the object 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 will cause the active system to measure the incorrect 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 relies on the fact that the Focus Level changes significantly when moving the lens back and forth. This permits the camera to stay on the best focus position. The Focus Level of low contrast objects doesn't change much and fails the passive system.

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