focal length

American  

noun

Optics.

1. the distance from a focal point of a lens or mirror to the corresponding principal plane. f

2. the distance between an object lens and its corresponding focal plane in a telescope.

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focal length British  

noun

1. the distance from the focal point of a lens or mirror to the reflecting surface of the mirror or the centre point of the lens

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focal length Scientific  

/ fō′kəl /

1. The distance between the optical center of a lens or mirror to its focal point.

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focal length Cultural  

1. The distance between the focal point of a lens (that is, the point at which the lens will focus parallel rays of light) and the lens itself.

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Etymology

Origin of focal length

First recorded in 1745–55

Example Sentences

It’s up to me then to define the focal length and the background and the angles, but it’s all based on his design.

From Los Angeles Times • Feb. 15, 2024

"They have a fixed focal length, a fixed size. They are made from materials that give you the lensing property you want, but they don't really have any dynamic characteristics."

From Science Daily • Oct. 23, 2023

The museum includes a camera the C.I.A. built for Mr. Tolkachev, with a fixed focal length to ensure his pictures would be less blurry.

From New York Times • Sep. 24, 2022

This also allows Apple to crop the sensor in different ways to deliver true 2x zoom at a 48mm focal length.

From The Verge • Sep. 7, 2022

He experimented in physical optics; took up astronomy in 1816; and in 1820, assisted by his father, he completed for a reflecting telescope a mirror of 18 in. diameter and 20 ft. focal length.

From Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 4 "Hero" to "Hindu Chronology" by Various