CRT projector
A CRT projector is a projector for playback of video and computer signals.
Technology
Unlike digital projectors such as LCD projector or DLP projector CRT projector does not use incandescent or metal halide lamp to produce light, but reflects the light produced by three electron tubes by means of very strong light optics directly on a canvas or in rear projection screen via a mirror and a Fresnel lens onto a screen. In principle, a CRT projector thus consists of three interconnected, each monochrome television sets whose images are congruent projected on a common canvas.
Advantages of CRT projectors are the natural color reproduction, ideal black level, long service life in video mode and an extremely high contrast. Due to the absence of a screen, as it is found in normal tube color TVs, also eliminates the festzustellende there and in LCD and plasma TVs screening, what a hassle scaling of all TV standards, including PAL, NTSC and HDTV (the latter only Multiscan units, horizontal frequency higher 15.75 kHz ) and allows an image with no flyscreen structure results. However, the devices in the so-called sweet spot should be operated in an area in which they deliver very bright images, while still able to map the required resolution sharp. Resolutions up to 1920x 1080 pixels are not uncommon, but these are merely an addressable resolution, not the optical. The optical resolution is dependent on many factors, a properly adjusted instrument provided the most important here: technical realization of the electrical focus of the electron beam electrostatically or better electromagnetically, the active tube size, ie unused image area on the tube, the phosphor mixture and the quality of the lenses.
However, direct activation of high-resolution multi-scan equipment is not readily possible because there will be more or less visible line structure of each video standard. There are scaler, line doubler or earlier quadrupler needed, interpolate the possible an integer multiple of the number of rows. The lifetime of the tubes is substantially higher than that of the lamps in the other types of projectors with up to 30,000 hours in the video mode.
As positive as well as negative values to the very short, fixed ratio of the distance from the screen is the image width; an image width of 2 meters is to accomplish distance without perspective distortion depending on the lens already at 2.2 meters. As mentioned, there is no zoom functionality. Otherwise, the convergence consuming to be set ( the three cathode ray tubes) would have to be readjusted again and again. A short distance from seat to the screen can be so really only by a ceiling-mounted unit realized.
Disadvantages are high weight ( from 35 kg), high price (NP from 10.000 € ), complicated installation (fixed installation is required, and the three images using test images through various analog or digital controller to get congruent, see convergence ), as well as the low absolute brightness, which makes the device useful only in relatively dim environment for desktop operation ( presentation). The latter is, however, in video mode not come to fruition due to the high peak brightness ( Kontrastverhältnis! ) and the small amount of white in video mode (film). To understand the effect of the peak brightness of the CRT projector: A 10 cm ² large white space on the screen is much brighter lit than one over the entire screen area distributed white space, depending on the device, the image is thus usually appear even brighter in video mode than in an equivalent digital projection. The tubes are also well as other tubes sensitive to penetration, so no possible still images should be displayed for a long period of time.
CRT projectors are manufactured by only a few manufacturers ( Barco, Runco, DC). Because of the high price and the video operation almost ideal characteristics but there is a very active market for used equipment.