focal length
Quick Summary
In optics, focal length is the distance from the center of a lens to the point where parallel rays of light converge to form an image. This distance is determined by the curvature of the lens's surfaces and the properties of the material it's made from.12
A lens's focal length is crucial for determining the size of the image it produces. A longer focal length lens will create a larger image of a distant object, while a shorter focal length lens will produce a smaller image. This principle is fundamental in various optical instruments, such as cameras, microscopes, and telescopes, where precise control over image formation is essential. The focal length is typically engraved on the lens mount, often in millimeters.132
Ask Britannica AI about this topic
Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.
telescopeRefracting telescopes…of refraction and the term focal length. The focus is the point, or plane, at which light rays from infinity converge after passing through a lens and traveling a distance of one focal length. In a refractor the first lens through which light from a celestial object passes is called…
Read More…of refraction and the term focal length. The focus is the point, or plane, at which light rays from infinity converge after passing through a lens and traveling a distance of one focal length. In a refractor the first lens through which light from a celestial object passes is called…
Read More- opticsThe Gauss theory of lenses
…respective focal points being the focal lengths of the lens, and, furthermore, that the two focal lengths are equal to one another when the refractive indices of object and image spaces are equal, as when a lens is used in air.
Read More…respective focal points being the focal lengths of the lens, and, furthermore, that the two focal lengths are equal to one another when the refractive indices of object and image spaces are equal, as when a lens is used in air.
Read More