CRT projector
A CRT projector is a video projector that uses a small, high-brightness cathode ray tube 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. The first color CRT projectors came out in the early 1950s. Most modern CRT projectors are color and have three separate CRTs, and their own lenses to achieve color images. The red, green and blue 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-CRT, which employed a phosphor 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.
Though systems utilizing projected video at one time almost exclusively used CRT projectors, they have largely been replaced by other technologies such as LCD projection and Digital Light Processing. Improvements in these digital video projectors, and their subsequent increased availability and desirability, resulted in a drastic decline of CRT projector sales by the late 2000s. As of 2012, very few new units are manufactured, though a number of installers do sell refurbished units, generally higher-end 8" and 9" models.
Advantages and disadvantages
Advantages
- Long service life; CRT's maintain good brightness to 10,000 hours.
- No bulbs to replace after only a couple thousand hours, however CRT projectors can accumulate burn-in if set to a high contrast value and/or displaying static content over time
- High-end CRT projectors can precisely display images up to 1920 x 1200 The Barco 912 claims an addressable resolution of 3200 x 2560, however with a bandwidth of 180 MHz it is not able to resolve fine detail at this resolution with the same clarity as other display technologies would
- Because of the good black levels, CRT projectors are good contenders to be used in edge-blend setups. DLP and LCD projector edge blend setups show a visible gray seam in the middle in dark scenes. Because of their 4:3 picture tubes, edge-blended CRTs use a larger surface area of the tubes when showing video in a cinemascope aspect ratio, which reduces uneven wear and yields higher total brigtness. CRT projector stacking is also possible.
- Superior overall black level compared to LCD and DLP based projectors, however some smaller air-coupled CRT projectors exhibit an effect known as blooming or haloing around bright objects displayed on a dark background
- 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 mechanisms.
- Zero input lag and zero motion blur, which makes them very suitable for video games of all kinds, as well video with fast motion
- Many CRT projectors are multiscan-capable, with a horizontal frequency range starting at 15KHz in the bottom end, on some projectors going all the way up to 150 or 180KHz. This means that CRT projectors are resolution compatible with a lot of video sources, including standard definition TV and retro games, VCRs, arcade games, older VGA computers, modern computers, HDTV, modern video game consoles, and more, without the need for upscaling or downscaling. This is advantageous over for example CRT computer monitors, of which all the ones from the mid-90s or later are also multisync capable, but have a lower frequency limit of 30KHz, making 480p60 or 240p120 the lowest resolution possible, thus needing upscaling to work with retro games and arcade games.
- CRT projectors do not show a rainbow effect seen with single chip DLP projectors.
- CRT projectors are made of three separate monochrome picture tubes, aimed, focused, converged on the same screen, thus there is no screen-door effect whatsoever is able to show distinctly sharp scan lines with black areas in between
- Some CRT projectors, like the Dwin 500 and 700, include no fans and are much quieter than comparable LCD or DLP projectors. Many CRT projectors feature large-size fans and temperature control and some can be easily modified for quieter and/or better performing cooling. The components in CRT projectors feature large surface areas compared to compact, bright Xenon-bulb lit DLP or LCD projectors.
- Three separate lenses reduce the risk of running into chromatic abberation problems in the corners of the picture, because each lens can be adjusted separately to account for three different wavelengths
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 lamp-powered LCD and DLP projectors.
- Low-end or poorly tuned CRT projectors may suffer from color divergence or geometric distortion.
- CRT projectors use more power / cost more to run than LCD and DLP units. It is however comparable to Plasma displays, which are also comparable in picture quality and performance.
- Unlike LCD or DLP projectors, CRT projectors are more prone to burn-in, if set to relatively a high contrast value and/or displaying static content for extended periods of time. This can lead to issues in brightness uniformity on projectors that frequently use both a full 4:3 and widescreen aspect ratio, as well as a change in colour temperature as the blue phosphors wear faster than the red. Overall burn-in is also a problem when moving or buying/selling CRT projectors, as different locations and different setups end up using different portions of the surface of the picture tubes.