What Does Focal Length Mean?
In optics and photography, the focal length is the distance from the optical center of the lens to the imaging sensor when the lens if focused at infinity. The focal length is measured in millimeters. Focal length directly affects the size of the image captured, as it changes the angle of view. Wider angle view and greater area are captured when the focal length is shorter.
Techopedia Explains Focal Length
In most cases in photography, lower optical power or longer focal length provides higher magnification. The angle of view in this case would be narrower. Conversely, higher optical power or short focal length is associated with lower magnification and wider angle of view. Focal length of the lens used in photography has many determining factors such as the radii of curvature, the medium in which the lens resides and the refraction index of the glass used for making the lens.
