A CRT projector is a video projector

Video projector

A video projector is an image projector that receives a video signal and projects the corresponding image on a projection screen using a lens system. All video projectors use a very bright light to project the image, and most modern ones can correct any curves, blurriness, and other...

 that uses a small, high-brightness CRT (or picture tube)

Cathode ray tube

The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...

 as the image generating element. The image is then focused and enlarged onto a screen using a lens kept in front of the CRT face. Most modern CRT projectors are color and have three separate CRTs (instead of a single, color CRT), and their own lenses to achieve color images. The red

Red

Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 630–740 nm. Longer wavelengths than this are called infrared , and cannot be seen by the naked eye...

, green

Green

Green is a color, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 520–570 nanometres. In the subtractive color system, it is not a primary color, but is created out of a mixture of yellow and blue, or yellow and cyan; it is considered...

 and blue

Blue

Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440–490 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal...

 portions of the incoming video signal are processed and sent to the respective CRTs whose images are focused by their lenses to achieve the overall picture on the screen. Various designs have made it to production, including the "direct" CRT-lens design, and the Schmidt

Schmidt-Cassegrain telescope

The Schmidt–Cassegrain is a catadioptric telescope that combines a cassegrain reflector's optical path with a Schmidt corrector plate to make a compact astronomical instrument that uses simple spherical surfaces.-Invention and design:...

-CRT, which employed a phosphor

Phosphor

A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...

 screen that illuminates a perforated spherical mirror, all within an evacuated "tube."

The image in the Sinclair Microvision "flat" CRT is viewed from the same side of the phosphor struck by the electron beam. The other side of the screen can be connected directly to a heat sink, allowing the projector to run at much brighter power levels than the more common CRT arrangement.

Advantages

• Long service life; CRT tubes maintain good brightness to 10,000 hours.
• High-end CRT projectors can precisely display images up to 1920 x 1200 with accurate color reproduction. A few projectors can scan at even higher resolutions up to 3200 x 2560, although their ability to resolve fine detail at this resolution is greatly reduced.
• Superior black level
  Black level
  Video black level is defined as the level of brightness at the darkest part of a visual image or the level of brightness at which no light is emitted from a screen, resulting in a pure black screen....
  
   compared to LCD and DLP based projectors.
• As with CRT monitors, the image resolution and the refresh rate are not fixed but variable within some limits. Interlaced material can be played directly, without need for imperfect deinterlacing
  Deinterlacing
  Deinterlacing is the process of converting interlaced video, such as common analog television signals or 1080i format HDTV signals, into a non-interlaced form....
  
   mechanisms.
• Very fast response time (especially when compared to LCD-based projectors), resulting in minimal (if any) motion blur
  Motion blur
  Motion blur is the apparent streaking of rapidly moving objects in a still image or a sequence of images such as a movie or animation. It results when the image being recorded changes during the recording of a single frame, either due to rapid movement or long exposure.- Photography :When a camera...
  
   when showing video with fast motion.
• CRT projectors do not show a Rainbow effect seen with single chip DLP projectors.

Disadvantages

• CRT projectors are both considerably larger and heavier than comparable LCD and DLP projectors.
• CRT projectors require far more time to set up and adjust than LCD and DLP based projectors.
• Absolute ANSI brightness achievable with CRT projectors is lower than with comparable LCD and DLP projectors.
• Low-end or poorly tuned CRT projectors may suffer from color divergence or geometric distortion (for example, straight lines may not always appear completely straight, especially near the corners).
• CRT projectors use more power / cost more to run than LCD and DLP units.
• Unlike LCD or DLP projectors, CRT projectors are somewhat prone to burn-in. This can lead to issues in brightness uniformity on projectors that frequently use both a full 4:3 and widescreen aspect ratio.

See also

• LCD projector
  LCD projector
  An LCD projector is a type of video projector for displaying video, images or computer data on a screen or other flat surface. It is a modern equivalent of the slide projector or overhead projector...
  
  
• DLP
• Barco
  Barco
  Barco N.V. is a display hardware manufacturer specialising in video projectors, LCD projectors, DLP projectors, LCoS projectors, LED displays, video walls, flat panel displays, automated luminaires, digital lighting and lighting controls....
  
  
• List of CRT video projectors

External links

• http://www.eisemann-theater.com/index.php?option=displaypage&Itemid=73&op=page] CRT Projector and Mod Specialist.