In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are, which is of great importance for the appearance at the image plane. If an aperture is narrow, then highly collimated rays are admitted, resulting in a sharp focus at the image plane. If an aperture is wide, then uncollimated rays are admitted, resulting in a sharp focus only for rays with a certain focal length. This means that a wide aperture results in an image that is sharp around what the lens is focusing on and blurred otherwise. The aperture also determines how many of the incoming rays are actually admitted and thus how much light reaches the image plane (the narrower the aperture, the darker the image for a given exposure time).

An optical system typically has many openings, or structures that limit the ray bundles (ray bundles are also known as pencils of light). These structures may be the edge of a lens or mirror, or a ring or other fixture that holds an optical element in place, or may be a special element such as a diaphragm placed in the optical path to limit the light admitted by the system. In general, these structures are called stops, and the aperture stop is the stop that determines the ray cone angle, or equivalently the brightness, at an image point.

In some contexts, especially in photography and astronomy, aperture refers to the diameter of the aperture stop rather than the physical stop or the opening itself. For example, in a telescope the aperture stop is typically the edges of the objective lens or mirror (or of the mount that holds it). One then speaks of a telescope as having, for example, a 100 centimeter aperture. Note that the aperture stop is not necessarily the smallest stop in the system. Magnification and demagnification by lenses and other elements can cause a relatively large stop to be the aperture stop for the system.

Sometimes stops and diaphragms are called apertures, even when they are not the aperture stop of the system.

The word aperture is also used in other contexts to indicate a system which blocks off light outside a certain region. In astronomy for example, a photometric aperture around a star usually corresponds to a circular window around the image of a star within which the light intensity is assumed.

Read more about Aperture:  Application, In Photography, In Scanning or Sampling

Other articles related to "aperture":

Aperture - In Scanning or Sampling
... The terms scanning aperture and sampling aperture are often used to refer to the opening through which an image is sampled, or scanned, for example in ... The sampling aperture can be a literal optical aperture, that is, a small opening in space, or it can be a time-domain aperture for sampling a signal waveform ... of film density fluctuations as seen through a 0.048 mm sampling aperture ...
Selenium Meter - Types of Meters - Coupled Meters
... More sophisticated cameras have the match-needle instrument coupled directly to aperture and shutter speed setting rings on the lens tube instead to a separate analog. 1960) the instruments were even used for setting exposure settings directly, mainly for automatic aperture setting ... gripped the meter needle, then moved an aperture control up to hit the needle, setting the aperture to a value controlled by the meter ...
Lenses For SLR And DSLR Cameras - Aperture and Depth of Field
... The aperture of a lens is the opening that regulates the amount of light that passes through the lens ... The relative aperture is specified as an f-number, the ratio of the lens focal length to its effective aperture diameter ... Aperture settings are usually not continuously variable instead the diaphragm has typically 5–10 discrete settings ...
Aperture Foundation
... The Aperture Foundation was founded in 1952 by Ansel Adams, Minor White, Barbara Morgan, Dorothea Lange, Nancy Newhall, Beaumont Newhall, Ernest Louie ... The first issue of Aperture (magazine) was published in spring 1952 in San Francisco ... Aperture's efforts increased respect for photography and its popularity among contemporary artists soared ...
Synthetically Thinned Aperture Radar
... Synthetic Thinned Aperture Radiometry (STAR) is a method of radar in which the coherent product (correlation) of the signal from pairs of antennas is measured at different antenna-pair spacings (baselines) ... Furthermore, aperture thinning reduces the overall volume and mass of the antenna system ... in signal-to-noise for each measurement compared to a filled aperture ...

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