what is aperture in camera

 

Aperture is an opening within the lens of a camera that limits the amount of light that enters the camera to make an exposure, it can be adjusted so as to change the depth-of-field. The size of this opening can be expressed in various ways such as f-stop or T-stop. It is one of three photographic components (along with shutter speed and ISO) that affect exposure. The other two components are generally referred to as the "exposure triangle".

The size of aperture affects not just the amount of light entering the camera, but also how much the lens acts to shape that light, since a small aperture produces a wide depth-of-field (DOF), and a large aperture makes the subject very sharp and in focus.

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The f-number is named for its usefulness in representing the ratio between focal length and focal depth of field. It is equal to f/2.8 or f/32 where "f" stands for focal length and "n" stands for one over that number. In 35 mm film photography, with a camera lens attached to a 35 mm camera body, typical starting values of aperture range from around f/2.8 to f/4 for wide-angle lenses, and from around f/4 to f/5.6 for normal and telephoto lenses, although many lenses are capable of taking considerably more extreme photographs. The smaller the number is the greater the depth of field is: large numbers indicate a narrow depth of field, small numbers indicate a large one. Aperture also affects exposure (see exposure triangle).

An optical system typically has many elements (lenses and other optical components), each with its own aperture stop that limits how much light passes through it. This aperture stop can be adjusted by the photographer while taking a photograph, in order to determine the size of the aperture opening, which in turn determines the amount of light that enters or is allowed to pass through the lens.

The name and concept of "aperture" is already quite old, dating back at least to Albertus Magnus (12 AD), who described how to use it as a factor in judging a picture's depth-of-field. The Italian scientist Leonardo da Vinci first described aperture as a function sometime before 1459: he did not call it such then, but later commentators have referred to it as "apertura" ("opening/gap"). Johannes Kepler described aperture in his "Dioptrice" (1611) as synonymous with entrance pupil, and the term became current in English in the late 18th century.

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The derivation of "aperture" from Latin "aperire", meaning 'to open', refers to increasing the area of the entrance pupil by reducing its size (the aperture stop) or increasing distance between lens and stop, or both. The opening can be as small as a few millimetres (with a 28mm f/2.8 lens, for example) to over an inch. The large aperture and short exposure times typical of SLR cameras and lenses make such apertures useful for photography in dim conditions, or with moving subjects.

Lenses with small maximum aperture, such as f/22, allow much more light to pass through the lens than larger lenses of the same focal length. The full width at half maximum (FWHM) of the photographic field is then determined by this aperture. The smaller the aperture, the greater this percentage will be. For example, an 18 mm lens set to f/22 admits 46% of the light that a 35 mm lens would with its aperture wide open at f/2.8 (the 35 mm is 46% of 18 mm).