What is Focal Length for a Camera Lens?

Focal length is a number (typically measured in millimeters) that determines the magnification power of the lens. Combined with the sensor size, the focal length can be used to determine the field (angle) of view of the camera. The number itself refers to the distance between the point where the light converges (Focal Point) and the image plane (sensor) when the subject is in focus at infinity. Shorter focal lengths correspond to a wider angle of view, and a longer focal length corresponds to a narrower angle of view.