Auto Focus in Cameras

Auto Focus - The camera will automatically focus the lens for a sharper picture and it helps to improve the quality of the pictures.

The working of auto focus in camera, we have small computer operated motors to move lens to get sharper images in this procedure the lens in the camera will move in and out till they calculate the distance from the object to get the sharper image. To calculate the distance from the object to camera, the infrared signal will be sent from the camera’s emitter, and when the infrared signal reflect back the camera will detect the signal and measures the intensity of infrared of light bounced back and measures the amount of time it takes to reflect back from object and the microprocessor in the camera will calculate the time and set the lens in the suitable position to capture the sharper image, this procedure is called active autofocus. today's cameras uses an infrared signal, and is great for subjects within 20 feet (6 m).

In this auto focus system we have passive systems, in this passive system to calculate the distance form the object we use the computer analysis of the image it self. This type of systems we can find in single lens reflex ( SLR) cameras with inter changeable lenses, and uses sensors that compute the contrast of the image. In this camera uses charge coupled device(CCD) to see light from the scene in this CCD we have strip of 100 to 200 pixels . In this passive system the camera continuously adjust the lens to capture the sharper image, the microprocessor searches for the greatest difference in intensity between lights and darks in adjacent pixels. This system will read vertical objects, so you should focus on a vertical edge like face of person or we can hold the camera in the vertical position for the horizontal objects like mountains. Now days we have a new cameras sensors which can focus on both vertical and horizontal objects.

Before the discovery of the auto focus cameras the people were using the manual focusing to get the sharpest picture and normal lens which are fixed in the cameras and not much expensive which gives the normal image.

We haves some defects with the auto focus system in cameras, In active auto focusing system the infrared sensing can get confused like if we take picture through window the infrared ray will reflect back because of the glass in the window and open flames in front of the camera like birth day candles can also confuse the sensors and drake surface will absorb the infrared ray.