Focal length is a term used in optics and photography to describe the distance between the optical center of a lens and the camera sensor or film where light information is recorded. It is a measure of how strongly an optical system converges or diverges light, and is the inverse of the systems optical power. A positive focal length indicates that a system converges light, while a negative focal length indicates that the system diverges light.
In photography, focal length is usually represented in millimeters (mm) and is not a measurement of the actual length of a lens, but a calculation of an optical distance from the point where light rays converge to form a sharp image of an object to the digital sensor or 35mm film at the focal plane in the camera. The focal length of a lens is determined when the lens is focused at infinity.
The focal length of a lens affects the angle of view and magnification of the image captured. The longer the focal length, the narrower the angle of view and the higher the magnification, while the shorter the focal length, the wider the angle of view and the lower the magnification.
In summary, focal length is a measure of how strongly an optical system converges or diverges light, and is represented in millimeters in photography. It affects the angle of view and magnification of the image captured.
