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Mangin mirrors were used in searchlights, where they produced a nearly true parallel beam. Many Catadioptric telescopes use negative lenses with a reflective coating on the backside that are referred to as “Mangin mirrors”, although they are not single-element objectives like the original Mangin, and some even predate Mangin's invention.
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Objective: The first lens or curved mirror that collects and focuses the incoming light. Primary lens: The objective of a refracting telescope. Primary mirror: The objective of a reflecting telescope. Corrector plate: A full aperture negative lens placed before a primary mirror designed to correct the optical aberrations of the mirror.
A convex secondary mirror is placed just to the side of the light entering the telescope, and positioned afocally so as to send parallel light on to the tertiary. The concave tertiary mirror is positioned exactly twice as far to the side of the entering beam as was the convex secondary, and its own radius of curvature distant from the secondary.
In ray diagrams (such as the images on the right), real rays of light are always represented by full, solid lines; perceived or extrapolated rays of light are represented by dashed lines. A real image occurs at points where rays actually converge, whereas a virtual image occurs at points that rays appear to be diverging from.
An oblique projection of a focus-balanced parabolic reflector. It is sometimes useful if the centre of mass of a reflector dish coincides with its focus.This allows it to be easily turned so it can be aimed at a moving source of light, such as the Sun in the sky, while its focus, where the target is located, is stationary.
Light path in a Cassegrain reflecting telescope. The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas, the main characteristic being that the optical path folds back onto itself, relative to the optical system's primary mirror entrance aperture.
Each optical element (surface, interface, mirror, or beam travel) is described by a 2 × 2 ray transfer matrix which operates on a vector describing an incoming light ray to calculate the outgoing ray. Multiplication of the successive matrices thus yields a concise ray transfer matrix describing the entire optical system.