Focusnig the camera involves adjusting the lens to adapt to the light.
For cameras to create images or photos, light must pass from the subject through a convex lens onto the film surface or sensor in the camera. The film surface or sensor creates a negative or upside down copy of the image. Photos are out of focus when the light from the subject passing through the lens hits the negative at a different point from the real image.
Manual Focus
When an image is out of focus on a camera the light passing through the convex lens of the camera is not hitting the same spot on the upside down negative as it is the real image. Moving the lens closer or farther from the real image changes where the light hits the negative, focusing the negative image.
Autofocus
Cameras with autofocus move the lens closer or farther from the real image automatically. Autofocus technology is very accurate, although most autofocus technologies struggle shooting dark settings or objects with no contrast or a single color. There are two types of autofocus: passive or active.
Passive Autofocus
Passive autofocus mimics the way people focus their cameras by selecting a focal point of the image and adjusting the lens. The autofocus typically focuses around the center of the image and the camera then directs the lens to move closer and farther from the image to decide on the best focus. Passive autofocus cameras struggle in dark settings because there isn't enough light entering the camera for it to see the object, adjust the focus and decide on the best focal point. Usually the camera will use a flash which white washes images and can distract from the subject. Passive autofocus cameras need contrast to find the focal point.
Active Autofocus
Active autofocus bounces a beam of infrared light from an emitter on the camera body to the subject and back to the camera. The beam measures the distance between the camera and the subject and sets the lens for the correct focus. Active autofocus struggles in settings with heat sources like candles that emit infrared light and other objects can absorb the invisible light causing out-of-focus shots. However, active focus doesn't have the same problems with no contrast subjects like white fences or walls because it measures distance rather than mimicking the human eye.
Tags: real image, closer farther, closer farther from, farther from, focal point, from real, from real image
