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Collimated (parallel) light waves converge through a lens, then diverge to be collimated by another lens, converging again through the lens of the eye. In geometrical optics, vergence describes the curvature of optical wavefronts. [1] Vergence is defined as =,
A perfectly collimated light beam, with no divergence, would not disperse with distance. However, diffraction prevents the creation of any such beam. [1] Light can be approximately collimated by a number of processes, for instance by means of a collimator. Perfectly collimated light is sometimes said to be focused at infinity.
A simple example of an afocal optical system is an optical telescope imaging a star, the light entering the system is from the star at infinity (to the left) and the image it forms is at infinity (to the right), i.e., the collimated light is collimated by the afocal system. [2]
If a collimated beam is focused with a lens, the diameter of the beam in the rear focal plane of the lens is related to the divergence of the initial beam by =, where f is the focal length of the lens. [1]
For a thin lens in air, the focal length is the distance from the center of the lens to the principal foci (or focal points) of the lens.For a converging lens (for example a convex lens), the focal length is positive and is the distance at which a beam of collimated light will be focused to a single spot.
The collimated transmission method has been used to measure the optical properties of biological tissues since the early 1980s. A collimated light source was generated by a laser or with a diffuse source and a collimator. Unscattered light transmission through the tissue was detected and Beer's law was used to estimate the extinction ...
Afocal photography works with any system that can produce a virtual image of parallel light, for example telescopes and microscopes. Afocal photographic setups work because the imaging device's eyepiece produces collimated light and with the camera's lens focused at infinity, creating an afocal system with no net convergence or divergence in the light path between the two devices. [2]
A refracting telescope commonly used is the Galilean telescope which can function as a simple beam expander for collimated light. The main advantage of the Galilean design is that it never focuses a collimated beam to a point, so effects associated with high power density such as dielectric breakdown are more avoidable than with focusing ...