To What Extent and for What Reasons does the Camera's Autofocus Function

When we press the shutter button, it's there for all of us to see. All current cameras have some kind of auto-focus feature built-in. Because of the auto-focus technology, we can now focus more on crafting the perfect shot and capturing the moment rather than worrying about manually adjusting the focus.

However, there are certain restrictions to autofocus. As an example, one can choose to take blurry images as an artistic statement. Also, the implementation of auto focus has its limits and may fail in specific cases. Take a photo of the blue sky using a high-end SLR camera that has passive autofocus. When a camera is unable to focus, it will often move its motor in an erratic manner until finally giving up and crashing.

Understanding how auto focus works will make it easier to put it to good use. It is possible to categorize all of the implementations into two groups: passive and active. The cheaper passive approach is used by most pocket cameras, but the active one or a mix of the two is used by high-end professional cameras.

Passive Auto Focus

Auto focus may be seen as mimicking the way we manually adjust the focus. When photographing, the camera creates one or more areas in the image (usually they are marked as rectangles on the viewfinder or the LCD). The focus level is then calculated by analyzing the image that is viewed in certain places. As it attempts to compute the focus level, the camera moves its lenses back and forth. The highest focus level is sought for by the camera. It would be considered in focus if the focus level was over a certain level at that instant.

There are several techniques to figure out your focus level. In all computations, the amount of contrast in the image serves as a common denominator. One technique to determine this number is to pass the picture through a high frequency filter, which is based on the idea that strong contrast is related to high frequencies. However, this method is beyond the scope of this article.

Autofocus That's on

The distance between the camera and the subject of the photograph is used to calculate the effectiveness of active auto focus. In theory, if you know exactly how far away the thing you're photographing is, you can set the lens to the precise focal point. The active focus technology uses an infrared beam to measure the distance to the item at the center of the image. Focus is determined by the distance from the camera to the subject.

All in One Focus

Some high-end cameras combine the two technologies into one unit for greater efficiency. Depending on the situation, the camera will employ either one of the two systems or a combination of the two. The photographer may also choose to employ one of the two alternatives at their own discretion. Using the active system, the camera may, for example, estimate the distance while capturing images of blue sky. Because the distance is unlimited, the camera is able to establish focus and avoid the passive focus that would otherwise be necessary. Cameras may also utilize the active system to place a lens in an estimated location and then fine-tune the position using the passive system when the distance is not infinite. Because the passive system is ineffective in low-light conditions, the camera may employ the active system instead.

So Why isn't the Camera's Auto Focus Always Working

There will always be situations when the camera's auto focus fails, despite all the electronics and computational power within. In certain cases, failure might occur because the camera is unable to focus and the image is blurry, while in other cases, the image is in focus but the camera "thinks" it is not.

What is the Reason for These Incidents? Even If the List is Lengthy, A Few Instances will Suffice

It is impossible for the passive auto focus system to operate in low light since it has to "see" the image in order to work. To get around this, some systems employ a succession of flashes, although this has been shown to be ineffective again and again. In these cases, an active system can estimate the distance to the item, but it will fail if the object is not in the center of the image or if there are many objects at varying distances.

Active systems may fail if the infrared beam they are employing tends to be absorbed by things. Infrared photons may be absorbed by certain materials, causing the active system to incorrectly calculate distance. Candles and open flame flames, among other infrared sources, may make the active system ineffective in certain situations.

White walls and blue skies are examples of low-contrast items. When shifting the lens back and forth, the focus level fluctuates dramatically. This is the basis for passive autofocus. This enables the camera to find the proper focus point and lock on. Low-contrast objects show little variation in the focus level, indicating a failure of the passive system.

The inability of a camera to properly focus may be explained in part by understanding how the autofocus technology works. The photographer has options in these situations. The photographer may have to employ manual focus at some point. It is possible to fix the difficulty by concentrating on another item in the image that is at the same distance, but it is much simpler to concentrate on.