Collimator

A collimator (Latin colinear " straight aim, judge" originally incorrectly read as colli mare ) is used to generate a parallel beam path, so for collimation. In technical optics is mapped using visible light with a collimator and a measuring scale at infinity.

Collimator for visible light

When using visible light is basically a hand in the technical optics, on the other hand, spoke in particular of a collimator:

  • Basically, by means of a lens L (see figure above ) turns the light of a more or less point source into a parallel beam. The light source is arranged in the front focal plane of the lens. Example is the dispersion prism a prism spectrometer upstream collimator lens ( see illustration ).
  • In particular, is located in the front focal plane of the lens, an illuminated measuring scale (eg a reticle ), which is mapped by means of a parallel beam path after the lens to infinity ( ∞). Such artificial target at an infinite distance is suitable for angle measurements, because it is insensitive to parallel displacement of the collimator. The measuring scale is in the focal plane of a telescope lens, an auxiliary device is created for review and adjustment of optical instruments. The connection of a collimator with its own lens with a superior telescope allows multiple applications in measurement tasks, especially in direction and angle determinations. A special collimator is the autocollimator (or autocollimator ), in which the light is reflected back from the rotatable measuring mirror to his starting point ( see illustration ). The sensitivity at the direction and angle determination is twice as large as the combination of a collimator and a telescope.

The focal length of a lens is defined for a mapping from the infinite. With the help of a collimator, a befindliches at a finite distance measurement object can be imaged with a lens to be examined from the infinite, with the main outer layers of the lens can be determined in addition to the focal length.

Light source / aperture / measuring scale and lens are often of an internally blackened tube ( tube) surrounded to keep out stray light. In order to reduce aberrations, either an aspheric lens or a system can be used from multiple lenses.

A similar function as the collimator lens, the collector of an illumination system for transmitted light microscopes. That with the collector initially directed parallel ( collimated ) light is then focused by a condenser lens in the lens.

Collimator for X-ray, gamma or particle

The simplest, most suitable choice of material suitable for almost any kind of radiation of the collimator is a block of a shielding material - for example, for X-ray or gamma radiation usually lead - with many thin, straight holes. Only radiation which extends approximately in the direction of the holes can pass through the collimator, all other rays are absorbed. Depending on the type ( thickness of the block and the diameter of the holes) and the type of initial beam passes, for example, less than one percent of the incident radiation through the collimator.

If the radiation source is almost point-like, is used as a collimator in simple cases, a block of material with a single bore.

Areas of application

Collimators are, inter alia in imaging in astronomy and medical applications, eg as a multileaf collimator in radiation therapy. Collimators look for radiation detectors used in which a pronounced preferential direction is needed. Using Autocollimators precise angle measurements can be made.

In the X-ray optics field as the collimator aperture can be used to control x-ray collimators, which are based not (only) on absorption, but at grazing reflection. In medical images, a collimator ( Buckyblende ) helps eliminate scattered radiation. Thus, the structure of the collimator is not mapped with, this can be moved during the exposure time, back and forth, which can be felt as a rumble audibly and on the pressed body.

In the military field, see collimators in reflective visors application to simplify the targets with firearms much. Originally also developed for military use, head- up displays can be found for representing information in the field of view of the pilot and nowadays also in civilian cars.

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