ABSTRACT
Focal Length The focal length of a lens determines the degree of magnification or de-magnification of the scene being shot. Different lenses offer different focal lengths. Focal length is determined by the distance between the optical center of the lens (the point at which the image flips) and the focal plane, φ. This distance is usually measured in millimeters (25mm, 75mm, 150mm, etc.), although older lenses may be marked in inches. The focal length of a lens affects both the image size within the frame and the angle of view, which means how much of the scene the lens takes in horizontally (x-axis) and vertically (y-axis).
