As the beam path of the geometric course of light rays through optical instruments ( microscopes, telescopes, projectors, Umbildegeräte, spectrographs, etc.) is called. The associated field is the geometrical optics ( ray optics ). It is assumed for simplicity that light consists of tiny particles ( photons) moving on a straight path, as long as they do not by lenses, mirrors (plane - curved), prisms or other optical components are distracted. And for the running direction of X-rays, this term is used.
In most optical instruments, the incident light is converged by an objective consisting of lenses and a primary mirror to the focal point, where it ( etc. camera, CCD sensor spectrograph ) is supplied either viewed through an eyepiece visual or other radiation detector. Often the beam is deflected by a plane mirror to make it more accessible to observation.
Astronomical mirror telescopes are usually in addition to the secondary mirror ( s) equipped to extend the focal length, astrographs also to their shortening. In photography, this contrast displaceable lens systems in use, such as a zoom lens.
In the design of an optical device is often the choice of lenses or mirrors to as main picture elements. Lenses have the advantage of a rather straight overall structure, with greater distances between them are easily bridged. Mirror there have advantages where the aim is compact, " folded " design and when it comes to observing broad spectral ranges, because with them, a typical lens errors such as chromatic aberration does not occur in principle.
In technical terms, mirrors have the advantage that they can be installed over the entire surface (not just at the edge, such as lenses ). They can be produced in larger dimensions, whereas telescope lenses are limited because of the lens bend to a maximum of 1m diameter. For glass lenses are more thermally stable than most of the mirror materials, as far as the focal length and shape changes.
Optical devices with optical path
In the projection optical systems, a concatenated beam is often used. Telecentric beam paths can be used when the image scale should be independent of the object distance or image distance or if distortions are to be avoided. In pericentric beam paths more side faces of an object can be recorded with a single figure.
The following is a selection of optical devices in which the beam path plays an important role:
- Light microscope
- Refracting telescope
- Reflecting telescope, especially those with folded beam path, among other things, Cassegrain, Coudé, Gregory and Nasmyth telescope
- Geometrical optics