Original sentence: Aperture diameter defines to the amount of light allowed through a lense system, and this is related to the length of time the sensor must be exposed to the in-coming light.Covering the lense partially prevents the focused beam from burning the paper because the intensity of light is reduced.Eventually, cameras opened and reduced the aperature automatically, and one only set the size to which the reduction would be stopped.F-number is a technical term used to describe the amount of light allowed through a lense system.Focal length is a simple way to describe the magnification capability of a lense.In order to make the preview as bright and easy to see as possible, the photographer would open the lense aperture as large as possible.Many people have an intuitive grasp of this because it can be demonstrated by burning paper with a magnifying glass in direct sunlight.Synonyms of f-number have been introduced over the years, many of which survive today.The aperture starts open and is "stopped down" to the appropriate diameter just prior to exposing the sensor.The focal length of the lense system is used because the intensity of light is concentrated at higher magnifications.The relationship between aperture diameter and exposure time is often quoted as lense speed.The term was originated when photographers used cameras that allowed the photographer to view the scene before exposing film.Then, before exposing the film, the photographer would close the aperture to account for film speed, motion, and depth of focus.These include: focal ratio, f-ratio, or relative aperture
Edited sentence: In optics, the f-number  (sometimes called focal ratio, f-ratio, or relative aperture) of an optical system expresses the diameter of the entrance pupil in terms of the effective focal length of the lens.It is the quantitative measure of lens speed, an important concept in photography