Projector

A projector (Latin proicere "forward throw, throw " ) is an optical device that allows a two-dimensional template (usually on a screen ) is imaged onto an image surface. In contrast to photography, the figure does not take place with the light of external light sources. A projector includes a light source other than a own lens. The original is a photographic or otherwise generated image. It is transparent (slides, negatives ) or non- transparent ( book pages, manuscript papers, paper pictures ), resting or moving ( motion picture ). It is mapped mostly increased. In overhead projectors the template is typically projected ( writing and drawing on transparent foil) while creating it.

Projectors for connecting digital template sources such as computers are called video projector or beamer shortly. At the site of the original one such projector has a device that converts the code of the electronic document at a photograph ( for optical imaging by means Projektonsobjektiv is the object ).

Laser projectors have no template that is projected. On the image surface of an image by controlling a laser beam is generated.

• 4.1 Classical projectors with real pictorial presentation
• 4.2 projectors with electronically coded template

By light and front projection

The terms rear projection and front projection relate to the type of lighting to be projected template.

Rear Projection Schematic of the illumination system of a slide projector, Slide immediately after right condenser

Rear Projection Overhead projector in operation, right: picture wall

Rear Projection Beam path in an overhead projector, Image the right (mirroring because submission of the screen facing )

Front projection Episkop, opaque template is pressed from below and lit from above

Front projection Beam path in a periscope, Image the right (mirroring because submission of the screen facing )

Rear Projection

Other transmitted light projectors are microfilm readers, overhead projectors, gobos, film viewers and magnifying devices.

For example, a slide - - In the rear projection to project the object is translucent. It is appeared from the light from the projector 's illumination device. The lighting can be optimized by means of interlaced with the imaging beam path illumination beam path: peak brightness, on the presentation of uniform illumination.

Front projection

In the front projection opaque templates ( flat items, paper images or illustrations from books ) project.). In contrast to the rear projection while the original is illuminated and viewed from the surface of the image side facing out. In the beam path there is an additional mirror, so the page is not shown reversed. Since only the reflected light from the document is to picture that the projection result is much less bright rear projection. The device's own light source is directed generally not perpendicular to the template, to avoid glare areas of the image on a glossy surface of the template. Illumination beam and imaging beam path are independent of each principle.

Template decoding

The decoder counteract the displayed image corresponding to light from a light source contained in the projector. The light is selectively into the beam path of the lens is deflected ( mirror at positions on / off or continuously variable reflectance). Other decoders allow light to pass through or not ( positions open / partially open / closed).

Video projector with DMD, schematically, Mirror array (DMD ) at the bottom right

Modern devices for decoding ( electro-optical conversion ) and large-area projection of an original electronically stored image are variants of the classical projection equipment. For them, the decoder takes the place of the generally non-variable real pictorial template. The decoder is a small area of deformed oil film at Eidophor device, a small area misaligned micromirror array (short DMD ) or an LCoS - matrix display with the video projector, the incident light as a function of the deformation of the oil film or the position of the mirror or the deformation of the LC - Molecular Structure the LCoS pixels reflect. Another common type of decoding is done when using the LCD video projector that let light through or not pass. The corresponding projectors are large areas displaying computer output devices.

Eidophorgerät with an analog composite image is generated. The video projectors produce since about 2005, only digitized (pixel ) images with the constructions mentioned above.

Laser projection

In laser projection are generated directly on the screen raster or vector-based graphics. There is no imaging optical lens by means of a rule. The laser projector to three grid-like (mostly by moving mirrors ) used across the projection guided laser beams of the primary colors red, green and blue, which can be individually modulated in their brightness.

The other hand, laser scanners generate one or more colored Illustrations.

A laser can be generated at light shows projections of individual lines and multiple lines. When used in single-line refractive optics ( Powell lenses, cylindrical lenses ), diffractive optical elements provide in combination with Powell lenses, the projection of multiple lines and matrices.

History

Traditional projectors with real pictorial presentation

By B. Della Porta in 1589, the magic lantern, a mirror - shadow device, described in detail. This equipment has been supplemented by Athanasius Kirchner in Rome with a converging lens, so was the first projector, led by improvements to the magic lantern of scholars Christian Huygens in 1659. The development was primarily driven by improved lighting systems with new lamps. 1872 replaced Marcy in Philadelphia " Skioptikon " oil lamp with a wick lamp kerosene flat, which were then replaced by the first projection bulbs. These units were built in various designs, fade, image change, fog projectors, wheel of life, endless projection, and more. By the early 20th century were offered combined projectors that worked both as a transmitted light as well as front projectors, ( epidiascopes ).

At the beginning of photography, it was only possible from photographic plates by contact copy to develop and look at photos. Later, techniques were developed to produce magnified images with a magnifying device or make it as a slide to a wider audience. Thus the way was paved for the small picture, as it was no longer necessary to photograph in the format of the resulting image.

The first small -screen slide projector comes from Leitz ( Wetzlar ) and published in 1926, a year after the first miniature camera ( Leica) was put on the market. This projector ( Uleja ) was the ancestor of all the slide projectors, with the magazine guide, autofocus, blending in technique and remote control enabled the viewing of slides later. In the course of digitization in photography, there are only a few manufacturers of these projectors.

In the European cinema projectors Ernemann, Goerz, Zeiss, Gaumont and AEG were most widespread in the silent 1920s. In the cinema of the so-called Abwinkler was very popular, a device which causes the images to fly to a certain extent out of space on the screen and back away from her.

A Vorführapparat, the particularly spared the footage in which the film band went through not jerky, but continuously, Ernst Leitz before: the Mechau projector, named after its inventor Emil Mechau. Despite some advantages, he was ultimately too big and too expensive to catch on in the cinemas can.

Projectors with electronically coded template

The first successful large-scale projection electronically coded images has been made possible by the ETHZ Professor Fritz Fischer in 1939 invented Eidophor method. On the market Eidophor systems were the early 1960s ( Swiss Gretag AG). Until the 1980s, this was the only way to large-scale video images in cinema size display. One of the customers was the U.S. space agency NASA, which used this system in a Space Operations.

CRT projectors used particularly bright cathode ray tubes whose image was projected through a lens onto a screen (Home cinema). More expensive models had three tubes, one for each primary color. Such 3CRT projectors were offered shortly after the introduction of color TV. The light intensity of such projectors was limited, so that only relatively small projection brought satisfactory results in darkened rooms.

In 1968 John A. van Raalte tried to deform instead of the oil layer used in Eidophor a liquid crystal layer according to the image content to modulate on this reflective layer the light in the RCA laboratories with an electron beam ( e-beam addressing engl. ).

With a transparent matrix form passively driven liquid crystal display ( LCD), mounted in a Diapositivrähmchen, Peter J. Wild led the research center of Brown, Boveri & Cie in 1971 in Baden and on a SID conference in 1972 an experimental LCD projector in transmitted light before. However, only a modest resolution with relatively few pixels was possible at that time with the liquid crystal displays available at that time.

Although the concept of active - matrix displays was tested with control via switching transistors assisted by Bernard J. Lechner at the RCA Laboratories in 1968 and known since 1971 and a Westinghouse team led by T. Peter Brody, the first laboratory version of an LCD matrix with control over thin film transistors ( TFTs) realized, it took several years until suitable TFTs integration of such combinations of LCD and TFT allowed for commercial products. First LCD video projectors this technique came from 1988 by the U.S. company Projectavision, Inc. and the Japanese vendors Sharp and Epson on the market and soon replaced the Eidophor systems.

The genesis of the various projection displays has been compiled in an English documentation from Texas Instruments (TI), with special emphasis on TI- invention of the Digital Light Processing (DLP ) using the Digital Micromirror Device (DMD ). Initially, printers and other applications have been developed with the original technology from around 1980. From 1989, a program was launched to develop appropriate projectors. The first commercially available DLP projector from TI was introduced in April 1996. The manufacturing of DLP projectors in Germany was of Liesegang with the projector " ddv 800" started in 1997.