From this definition, it can be shown that the AFOV of a lens is related to the focal length ( Equation 1 ), where f f is the focal length and H H is the sensor size ( Figure 1 ). German: Brennweite. The focal length of a lens is the optical distance (usually measured in mm) from the point where the light meets inside the lens to the camera’s sensor. The focal length is part of another formula which allows for calculating the focal ratio of a telescope. Category: general optics. Encyclopedia > letter F > focal length. Definition: a measure of how strongly an optical system focuses or defocuses light. . This is because the perspective of a 50mm lens closely resembles that of … The focal length defines the magnification and field of view for a given lens. Let’s say you have a reflecting telescope with an aperture of 6 inches (152.4mm) and a focal length of 1000mm, your focal ratio is 1000/152.4= 6.56! The focal length of a lens is a measurement (in millimeters) that indicates the distance between the center of a lens and its focus point. Focal length is a well known word in optical physics. Focal length is the distance between the optical center of the lens, and the camera sensor or film plane when focused at infinity. Formula symbol: f Units: m. How to cite the article; suggest additional literature. From selecting the right lens, to getting those picture-perfect shots, read on to learn more about focal length and how it impacts photography. The optical center is where light rays converge inside the body of your lens. This time, you will need to divide the focal length by the aperture of the telescope. The focal length of a lens determines what your camera can focus on, and how your images are going to turn out. Focal Length. Thus, for convex lens, the focal length is a distance over which all the parallel rays will converge. On the other hand, the focal length of concave lens is negative. • The back focal length BFL is the distance between the rear vertex V’ of the lens, and the rear focal point F’. That’s just cropping your photo before you actually take it,” … Understanding focal length is key to understanding how your camera works. (1) AFOV = 2×tan−1( H 2f) AFOV = 2 × tan − 1. Meaning of Focal length. The simplest focal length definition is a description of the distance between the center of a lens and the image sensor when the lens is focused at infinity. Information and translations of Focal length in the most comprehensive dictionary definitions resource on the web. ( H 2 f) Figure 1: For a given sensor size, H, shorter focal lengths produce wider AFOV’s. Generally speaking, it refers to how long the lens is. “You can zoom in on your phone, but that’s not changing your focal length. Focal length is distance over which the parallel rays either converge or diverge. FOCAL LENGTH DEFINITION What is focal length? On super 35mm film, or an equivalent-sized sensor, such as on the ALEXA, a 50mm lens is typically considered a “normal lens.”. • By definition, the effective focal length EFL is the distance between the rear principal point P’, and the rear focal point F’ of the lens. Definition of Focal length in the Definitions.net dictionary. If you would put a 35mm lens on the Canon 70D, you would roughly get a look of a 50mm on a full-frame camera. Author: Dr. Rüdiger Paschotta Various types of optical systems (e.g. For convex lens the focal length is positive. Focal Length Definition. That technical definition isn't really what's important when learning about focal length, however. • The front focal length FFL is the distance between the front focal But, with a Canon 70D the focal length of the lens is multiplied with the crop factor (50×1.6), resulting in a focal length or angle of view of 80mm. 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