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, apertures":
... perfectly a finite plane (the object) onto another plane (the image) through a finite aperture ... and the deviation from the sine condition small throughout the whole aperture, there is given to a ray with a finite angle of aperture u* (width ... The rays with an angle of aperture smaller than u* would not have the same distance of intersection and the same sine ratio these deviations are called zones, and the constructor endeavors to reduce these to a minimum ...
... Aperture sights, also known as peep sights, range from the ghost ring sight, whose thin ring blurs to near invisibility (hence ghost), to target aperture sights that use large disks or other occluders with pinhole-size ... the sight picture taken through large and small diameter apertures ... The large diameter aperture provides a much brighter image of the target, and the ghosting of the rear ring is evident ...
... For a given numerical aperture (NA), the resolution of microscopy for flat objects under coherent illumination can be improved using interferometric microscopy ... recording of the distribution of the complex optical field, the large aperture image can be reconstructed numerically ... Microscopy uses two opposing objectives to double the effective numerical aperture, effectively halving the diffraction limit ...
... The angular aperture of a lens is the apparent angle of the lens aperture as seen from the focal point where is the focal length is the diameter of the aperture ...
... 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 a Drum ... 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 ... as graininess via a measurement of film density fluctuations as seen through a 0.048 mm sampling aperture ...
Famous quotes containing the words stop and/or aperture:
“The mastery of one’s phonemes may be compared to the violinist’s mastery of fingering. The violin string lends itself to a continuous gradation of tones, but the musician learns the discrete intervals at which to stop the string in order to play the conventional notes. We sound our phonemes like poor violinists, approximating each time to a fancied norm, and we receive our neighbor’s renderings indulgently, mentally rectifying the more glaring inaccuracies.”
—W.V. Quine (b. 1908)
“Animals used to provide a lowlife way to kill and get away with it, as they do still, but, more intriguingly, for some people they are an aperture through which wounds drain. The scapegoat of olden times, driven off for the bystanders’ sins, has become a tender thing, a running injury. There, running away ... is me: hurt it and you are hurting me.”
—Edward Hoagland (b. 1932)