Educational Significance of Projected Audio Visual Aids

Lesson in Glance

Classification
    Episcope or Opaque Projector
 Diascope
 epidiascope
EPISCOPE OR OPAQUE PROJECTOR
Episcope displays opaque materials by shining a bright lamp onto the object from above.
Opaque projector is the only projector on which you can project a variety of materials ex: - book pages, objects, coins, postcards, or any other similar flat material that is non-transparent.
Parts Of Episcope
1.Reflector- Plane mirror
2.Projection Lens-Converging Lens
3.Source of Light or Projection Lamp
4.Objects and Image

Advantages Of Episcope
Stimulates attention and arouses interest. 
Can project a wide range of materials like stamps, coins, specimen, when one copy is available.    
Can be used for enlarging drawings, pictures and maps.  
Does not require any written or typed materials, hand-written material can be used.
Helps students to retain knowledge for longer period.
Review instructional problems.
Test knowledge and ability.
Simple operation
 
Disadvantages Of Episcope
   Costly equipment.
   Needs to use it with care.
   Needs a dark room for    projection.
 
DIASCOPE
Diascope is used for projecting transparent materials.
 

The important diascopes

Slide Projector
Filmstrip Projector,
Over Head Projector

Slide Projector

A slide projector is an opto-mechanical device to view photographic slides
A projector has four main elements:
A fan-cooled electric incandescent light bulb or other light source
reflector
"condensing" lens to direct the light to the slide
slide holder
focusing lens
Slides
Slides are a form of projected media that are easy to prepare.

Types Of Slides

Photographic slides: Both  black and white and colored slides.
Hand made slides: can be made with
a)      Acetate sheet
b)      Cellophane
c)      Etched glass
d)      Plain glass
e)      Lumarith       
 

 Advantages:

1.      Requires only filming, processing and mounting by self or laboratory.

 2.      Results in colorful, realistic, reproduction original subject.

3.     Preparation with any 35mm camera for most uses.

4.      Easy to revise and up-date.

 5.      Easily handled, stored and re-arranged for various uses.

 6.      Can be combined with tape narration or can control time for discussion.

7.      May be adapted to group or individual use

 
Filmstrips and Filmstrip Projector,
Film strips are sequence of transparent still pictures with individual frames on 35mm film.
Each strip contains from 12 to 18 or more pictures. It is a fixed sequence of related stills on a roll of 35mm film or 8mm film
Film strips accompanied by commentary are called Sound filmstrip
Advantages:
1)      Are compact, easily handled and always in proper sequence.
2)      Can be supplemented with recordings.
3)      Are inexpensive when quantity reproduction is required.
4)      Are useful for group or individual study at projection rate are controlled by instructor or user.
5)      Are projected with simple light weight equipment.
 
Over Head Projector
The over head projector projects transparencies with brilliant screen images suitable for use in lighted room.
The name comes from the fact that the projected image is behind and over the head of the speaker

An overhead projector typically consists of

A large box containing a very bright lamp and a fan to cool it.
A large Fresnel Lens  that collimates  the light.
A mirror and lens that focuses and redirects the light.
Over Head Projector
Advantages Of OHP
It permits the teacher to stand in front of the  class while using the projector, thus enabling her to point out features appearing on the  screen by pointing to the materials at the projector itself  and at the same  time, to observe the students reactions to her discussion.
 Gains attention of the student.
Lighted Room.
Large image
Flexibility and versatility
 
EPIDIASCOPE
The epidiascope is a type of opaque projector developed in the early years of the 20th century. Epidiascopes can project images of both transparent and opaque images.
An epidiascope serves two purposes. It works as episcope when it is used to project opaque objects and works as diascope when it is used to project slides.
LCD PROJECTOR
An LCD (Liquid Crystal Display) projector is a type of video projector for displaying videos images or computer data on a screen or flat surface

 

To display images LCD Projectors send light from a halogen lamp through three LCD panels –one each for red blue and green components of video signal.
Educational values of LCD
LCD projector technology enables educators to present multimedia content appropriate for a variety of students with different learning styles. Students with auditory, visual or kinesthetic learning styles benefit from engaging multimedia lessons that correlate with their strengths.
Students can participate in real-time, interactive activities. Problem-solving activities promote the development of critical thinking skills.
Students work collaboratively in groups and make their own presentations to the class. They can learn valuable social-emotional, technology and communications skills.
 
 DLP PROJECTOR
Digital Light Processing (DLP) is a display technology developed by Texas Instruments.
The first DMD chip was invented by Larry Hornbeck in 1987.
In DLP projectors, the image is created by microscopically small mirrors laid out in a matrix on a semiconductor chip, known as a Digital Micro mirror Device (DMD). Each mirror represents one or more pixels in the projected image. The number of mirrors corresponds to the resolution of the projected image.
Creation of color image in DLP
There are two primary methods by which DLP projection systems create a color image, those utilized by single-chip DLP projectors, and those used by three-chip projectors.
In a projector with a single DLP chip, colors are either produced by placing a color wheel between the lamp and the DLP chip or by using individual light sources to produce the primary colors, LEDs or LASERs for example.
A three-chip DLP projector uses a prism to split light from the lamp, and each primary color of light is then routed to its own DLP chip, then recombined and routed out through the lens.
DLP Features
Clarity
Brightness
Colour
Reliability
Life-span:
Disadvantages of DLP Projector
Some viewers are bothered by the "rainbow effect" - particularly in older models .
Rear projection DLP TVs are not as thin as LCD or plasma flat-panel displays
Replacement of the lamp / light bulb in lamp based units. The average life span of a mercury lamp averages 2000–5000 hours and the replacement cost for these range from $99 – 350, depending on the brand and model. Newer generations' units use LEDs or lasers which effectively eliminate this issue, although replacement LED chips could potentially be required over the extended lifespan of the television set.
Some viewers find the high pitch whine of the color wheel to be an annoyance  though the drive system can be engineered to be silent and some projectors don't produce any audible color wheel noise.
 
Disadvantages of DLP Projector
Dithering noise may be noticeable, especially in dark image areas. Newer (post ~2004) chip generations have less noise than older ones.
Error-diffusion artifacts caused by averaging a shade over different pixels, since one pixel cannot render the shade exactly.
Response time in video games may be affected by upscaling lag. While all HDTVs have some lag when upscaling lower resolution input to their native resolution, DLPs are commonly reported to have longer delays. Newer consoles such as the  do not have this problem as long as they are connected with HD-capable cables.
Reduced viewing angle as compared to direct-view technologies such as CRT, plasma, and LCD
May use more electricity, and generate more heat, than competing technologies.
Some people may be able to observe a phenomenon in which the projected contents appear to be cycling through it colours for the duration of the presentation. This is most easily seen by using a camera's 'live view' mode on projected content.
 
CRT(Cathode Ray Tube) 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.
Advantages of CRT projector
Long service life.
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  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. Interlace material can be played directly, without need for imperfect deinterlacing mechanisms.
Very fast response timer. 
CRT projectors do not show a Rainbow effect  seen with single chip DLP projectors.

  Disadvantages of CRT projector

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.
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.

 

 

1.      EPISCOPE OR OPAQUE PROJECTOR

 Opaque projector is the only projector on which you can project a variety of materials ex: - book pages, objects, coins, postcards, or any other similar flat material that is non-transparent. The opaque projector will project and simultaneously enlarge, directly from the originals, printed matter, all kinds of written or pictorial matter in any sequence derived by the teacher. It requires a dark room, as projector is large and not reality movables.

Episcope displays opaque materials by shining a bright lamp onto the object from above. A system of mirrors, prisms and/or imaging lenses is used to focus an image of the material onto a viewing screen. Because they must project the reflected light, opaque projectors require brighter bulbs and larger lenses than overhead projectors. Care must be taken that the materials are not damaged by the heat generated by the light source.

Advantages

  • Stimulates attention and arouses interest. 
  • Can project a wide range of materials like stamps, coins, specimen, when one copy is available.    
  • Can be used for enlarging drawings, pictures and maps.  
  • Does not require any written or typed materials, hand-written material can be used.
  • Helps students to retain knowledge for longer period.
  • Review instructional problems.
  • Test knowledge and ability.
  • Simple operation

Disadvantages:

         costly equipment.

         needs to use it with care.

         needs a dark room for projection.

  1. 2.      DIASCOPE

Diascope is used for projecting transparent materials. The important diascopes are slide projector, filmstrip projector, OHP etc.

i)     Slide Projector

A slide projector is an opto-mechanical device to view photographic slides. A projector has four main elements: A fan-cooled electric incandescent light bulb or other light source , reflector and "condensing" lens to direct the light to the slide, slide holder, focusing lens. A flat piece of heat-absorbing glass is often placed in the light path between the condensing lens and the slide, to avoid damaging the latter. This glass transmits visible wavelengths but absorbs infrared. Light passes through the transparent slide and lens, and the resulting image is enlarged and projected onto a perpendicular flat screen so the audience can view its reflection. Alternatively, the image may be projected onto a translucent "rear projection" screen, often used for continuous automatic display for close viewing. This form of projection also avoids the audience interrupting the light stream by casting their shadows on the projection or by bumping into the projector.

Slides

Slides are a form of projected media that are easy to prepare. They are still pictures on positive film which you can process and mount individually yourself or send to a film laboratory. The standard size of the slides is 2 “X 2 “any 35mm camera will make satisfactory slides.

 Types of slides

1.   Photographic slides: Both  black and white and colored slides.

2. Hand made slides: can be made with

a)      Acetate sheet

b)      Cellophane

c)      Etched glass

d)      Plain glass

e)      Lumarith       

Slides can be made from photographs and pictures by teachers and pupils taking photographs and snapshots when they go on fieldtrips for historical, geographical, literacy or scientific excursions. The arrangement of slides in proper sequence, according to the topic discussed, is an important aspect of teaching with them.

Advantages:

1.      Requires only filming, processing and mounting by self or laboratory. 2.      Results in colorful, realistic, reproduction original subject.

 3.     Preparation with any 35mm camera for most uses.

4.      Easy to revise and up-date.

 5.      Easily handled, stored and re-arranged for various uses.

 6.      Can be combined with tape narration or can control time for discussion. 7.      May be adapted to group or individual use

ii)    Over Head Projector:

The over head projector projects transparencies with brilliant screen images suitable for use in lighted room. The teacher can write or draw diagrams on the transparency while he teaches; these are projected simultaneously on the screen by the over head projector (OHP). The name comes from the fact that the projected image is behind and over the head of the speaker. An overhead projector typically consists of a large box containing a very bright lamp and a fan to cool it. On top of the box is a large fresnel lens that collimates the light. Above the box, typically on a long arm, is a mirror and lens that focuses and redirects the light forward instead of up.

Transparencies are placed on top of the lens for display. The light from the lamp travels through the transparency and into the mirror where it is shone forward onto a screen for display. The mirror allows both the presenter and the audience to see the image at the same time, the presenter looking down at the transparency as if writing, the audience looking forward at the screen. The height of the mirror can be adjusted, to both focus the image and to make the image larger or smaller depending on how close the projector is to the screen.

Focal-length adjustment

Better-quality overhead projectors offer an adjustment wheel or screw on the body of the projector, to move the lamp towards or away from the fresnel lens. When the mirror above the lens is moved too high or too low, it moves out of the best focal distance for an evenly white image, resulting in a projected image with either blue or brown color fringing around the outside edge of the screen. Turning the adjustment wheel moves the lamp to correct the focal distance and restores the all-white projected image.

Illumination

The lamp technology of an overhead projector is typically very simple compared to a modern LCD or DLP video projector. Most overheads use an extremely high-power halogen lamp that may consume up to 750 watts yet produces a fairly dim, yellowed image. A high-flow blower is required to keep the bulb from melting itself due to the heat output. Further, the intense heat usually causes the halogen lamp to fail quickly, often lasting less than 100 hours before failing and requiring replacement. A modern LCD or DLP uses an arc lamp which has a higher luminous efficacyand lasts for thousands of hours. A negative to LCD/DLP technology is the warm up time required for arc lamps.

Older overhead projectors used a tubular quartz lamp body containing the filament only, which mounted above a bowl-shaped polished reflector. However because the lamp was suspended above and outside the reflector, a large amount of light was cast to the sides inside the projector body that was wasted and required a very large lamp for sufficient screen illumination. More recent projectors use an integrated lamp and conical reflector assembly that allows the lamp to be located deep within the reflector so that more light is focused towards the fresnel lens, allowing for a lower-power lamp.

For effective presentation using OHP

   Keep the screen above the heads of the participants.

   Keep the screen in full view of participants.

   Make sure you are not blocking any ones view when presenting.

   Darken the room appropriately by blocking out sunshine and dimming nearby.

   Turn the screen off between slides if you are going to talk for more than two.

   Talk to the audience, not to the screen

Purposes of using OHP

  To develop concepts and sequences in a subject matter area.

  To make marginal notes on the transparencies for the use of the teacher that can carry without exposing them to the class.

  To test students performances, while other classmates observe.

  To show relationships by means of transparent overlays in contrasting color.

  To give the illusion of motion in the transparency.

Advantages

  It permits the teacher to stand in front of the  class while using the projector, thus enabling her to point out features appearing on the  screen by pointing to the materials at the projector itself  and at the same  time, to observe the students reactions to her discussion.

  Gains attention of the student.

Over Head Transperencies:

     Transparencies are popular instructional medium. They are simple to prepare and easy to prepare and easy to operate with the over head projector which is light weight. A 10*10 inches sheet with printed, written or drawn material is placed on the platform of the projector and a large image is projected on a screen behind you. The projector is used from near to the front of the room with the teacher standing or sitting beside, facing the student.

Guidelines for making effective transparencies:

         Have one main idea an each transparency.

         Include only related figures and diagrams.

         Use simple lettering style in writing.

         Use diagrams in proposition to its lettering.

         Keep the message clear and simple.

         Emphasize the key messages.

         Use color and lettering with discretion.

Advantages

         Permits face to face interaction with the students.

         Can be used in daylight conditions.

         Can present information in systemic developmental sequences.

         Requires limited planning and can be prepared in variety of inexpensive methods.

         Easily available.

Guidelines for making effective transparencies:

         Have one main idea an each transparency.

         Include only related figures and diagrams.

         Use simple lettering style in writing.

         Use diagrams in proposition to its lettering.

         Keep the message clear and simple.

         Emphasize the key messages.

         Use color and lettering with discretion.

Advantages:

         Permits face to face interaction with the students.

         Can be used in daylight conditions.

         Can present information in systemic developmental sequences.

         Requires limited planning and can be prepared in variety of inexpensive methods.

         Easily available.

iii)  Film Strips and Film Strip Projector                

Film strips are sequence of transparent still pictures with individual frames on 35mm film. A tap recorded narration can be synchronized with film strip. Each strip contains from 12 to 18 or more pictures. It is a fixed sequence of related stills on a roll of 35mm film or 8mm film.

Principles

1.      Preview filmstrips before using them and selected carefully to meet the needs of the topic to be taught.

2.      Show again any part of the filmstrip needing more specific study.

3.      Use filmstrip to stimulate emotions, build attitudes and to point up problems.

4.      It should be introduced appropriately and its relationship to the topic of the study brought out.

5.      Use a pointer to direct attention, to specific details on the screen.

Types of filmstrip:

1)      Discussion filmstrip: it is continuous strip of film consisting of individual frames arranged in sequence usually with explanatory titles.

2)      Sound slide film: it is similar to filmstrip but instead of explanatory titles or spoken discussion recorded explanation is audible, which is synchronized with the pictures. Advantages:

1)      Are compact, easily handled and always in proper sequence.

2)      Can be supplemented with recordings.

3)      Are inexpensive when quantity reproduction is required.

4)      Are useful for group or individual study at projection rate are controlled by instructor or user.

5)      Are projected with simple light weight equipment.

iv)    Magic Lantern

The magic lantern used a concave mirror in back of a light source to direct as much of the light as possible through a small rectangular sheet of glass—a "lantern slide"—on which was the painted or photographic image to be projected, and onward into a lens at the front of the apparatus. The lens was adjusted to optimally focus the plane of the slide at the distance of the projection screen, which could be simply a white wall, and it therefore formed an enlarged image of the slide on the screen.

Apart from sunlight, the only light sources available at the time of invention in the 16th century were candles and oil lamps, which were very inefficient and produced very dim projected images. The invention of the Argand lamp in the 1790s helped to make the images brighter. The invention of limelight in the 1820s made them very much brighter. The invention of the intensely bright electric arc lamp in the 1860s eliminated the need for combustible gases or hazardous chemicals, and eventually the incandescent electric lamp further improved safety and convenience, although not brightness.

The magic lantern was not only a direct ancestor of the motion picture projector, but it could itself be used to project moving images, which was achieved by the use of various types of mechanical slides. Typically, two glass slides, one with the stationary part of the picture and the other with the part that was to move, would be placed one on top of the other and projected together, then the moving slide would be hand-operated, either directly or by means of a lever or other mechanism. Chromotrope slides, which produced eye-dazzling displays of continuously cycling abstract geometrical patterns and colors, were operated by means of a small crank and pulley wheel that rotated a glass disc.

  1. 3   EPIDIASCOPE

The epidiascope is a type of opaque projector developed in the early years of the 20th century. Epidiascopes can project images of both transparent and opaque images. This quality made the device especially useful in educational circles for most of the century.The basic functionality of the epidiascope involved harnessing the power of light to create the images. In the earliest models of the epidiascope and other similar projectors, limelight was used as the medium. The light would be directed downward onto an object, creating the image. To focus the light and create a viable image, a series of lenses or mirrors would be used to direct the image onto a screen. While somewhat costly to produce at first, the epidiascope became more affordable as the device was refined. Along with commercial models, low powered versions were produced and marketed as toys for school age children.By the middle of the 20th century, the typical epidiascope was produced using incandescent light as the source for creating the image. Desktop models of the device were in common use in schools and colleges across the globe. Within a few years, halogen lamps began to replace the incandescent bulbs, providing an even sharper projected image.

With the help of any epidiascope, any chart, diagram, map, photograph and picture can be projected on the screen without tearing it off from the book. No slide is needed for this purpose. An epidiascope serves two purposes. It works as episcope when it is used to project opaque objects and works as diascope when it is used to project slides.  It works on the principle of horizontal straight line projection with a lamp, plane mirror and projection lens. A strong light from the lamp falls on the opaque object. A plane mirror placed at an angle of 45" over the project reflects the light so that it passes through the projection lens forming a magnified image on the screen.

                                            LCD PROJECTOR

Educational values of LCD

  • LCD projector technology enables educators to present multimedia content appropriate for a variety of students with different learning styles. Students with auditory, visual or kinesthetic learning styles benefit from engaging multimedia lessons that correlate with their strengths.
  • Students can participate in real-time, interactive activities. Problem-solving activities promote the development of critical thinking skills.
  • Students work collaboratively in groups and make their own presentations to the class. They can learn valuable social-emotional, technology and communications skills.

 

                                          DLP PROJECTOR

Digital Light Processing (DLP) is a display technology developed by Texas Instruments. The first DMD chip was invented by Larry Hornbeck in 1987. Larry, a scientist at Texas Instruments, had been exploring the manipulation of reflected light since 1977. He developed the Digital Micro mirror Device, or DMD: an optical semiconductor capable of steering photons with unparalleled accuracy. This digital micro-mirror - greatly refined - is the basis of modern DLP technology.

In DLP projectors, the image is created by microscopically small mirrors laid out in a matrix on a semiconductor chip, known as a Digital Micro mirror Device (DMD). Each mirror represents one or more pixels in the projected image. The number of mirrors corresponds to the resolution of the projected image. 800x600, 1024x768, 1280x720, and 1920x1080 (HDTV) matrices are some common DMD sizes. Rapidly toggling the mirror between these two orientations (essentially on and off) produces gray scales, controlled by the ratio of on time to off time.

There are two primary methods by which DLP projection systems create a color image, those utilized by single-chip DLP projectors, and those used by three-chip projectors. In a projector with a single DLP chip, colors are either produced by placing a color wheel between the lamp and the DLP chip or by using individual light sources to produce the primary colors, LEDs or LASERs for example. A three-chip DLP projector uses a prism to split light from the lamp, and each primary color of light is then routed to its own DLP chip, then recombined and routed out through the lens. Three chip systems are found in higher-end home theatre projectors, large venue projectors and DLP Cinema projection systems found in digital movie theatres.

DLP Features

 Clarity: DLP technology comes closer than any other display solution to reproducing the exact mirror image of its source material. That’s why images projected by DLP technology are always crystal clear. The thousands of mirrors making up the DMD at the heart of DLP technology are spaced less than one micron apart, resulting in a very high ‘fill factor.’ By

minimising the gaps between pixels in a projected image, DLP projection systems create a seamless digital picture.

Brightness: DLP projection systems outshine the alternatives because, being mirror-based, they use light more efficiently. While other technologies lose a certain amount of light in transit, the microscopic mirrors in a DLP projection system bring more light from lamp to screen.

Colour: DLP technology reproduces a range of colours up to eight times greater than of analogue projection systems. In televisions and home theatre systems, DLP projection creates

rich blacks and darker shades than is possible with other technologies. At the movies, DLP Cinema technology projects no fewer than 35 trillion colours. DLP colours are becoming even more brilliant with the introduction of sequential colour recapture or SCR—an innovation that will enable DLP projection systems (video projectors) to bring up to 40 per cent more lumens to the screen than was possible earlier.

Reliability: DLP technology makes video projectors, home theatre systems and televisions more robust and more reliable. The digital nature of DLP technology means that, unlike other display solutions, it’s not susceptible to heat, humidity or vibration—environmental

factors that can cause an image to degrade over time. DLP projection systems display

an original-quality picture time and again with no hassle and minimal maintenance. More than one million systems have been shipped since 1996.

Life-span: A DLP-based HDTV set should last indefinitely because the digital micromirror device behind it is very reliable. There is no maintenance or alignment required for DLP-based sets as they age. The only consumer replaceable component is the DLP light source (lamp), which will last for 8000 hours and costs around $250 to replace.

 Advantages of DLP Projector

 a) Brighter: DLP projectors are among the brightest available because DLP technology brings more light from lamp to screen, resulting in more effective presentations—even when ambient light is difficult to control.

 b) Sharper: DLP projection’s unique reflective technology comes closest to producing the exact mirror image of an incoming video or graphic signal, resulting in projection that’s seamless.

 c) Versatile: DLP technology allows projectors to be small and light, often weighing as little as 1 kg—making them versatile enough for use in conference rooms, living rooms and classrooms.

 d) More reliable: Display systems using DLP technology are able to recreate their incoming source material with each projection, ensuring a full-impact projection experience that will not fade over time.

 e) Consistent picture quality: A data projector based on DLP technology delivers knockout picture quality again and again because, being all-digital, it recreates its image source every time of use. Unlike competing analogue technologies such as LCD, the semiconductor that makes DLP projection possible is virtually immune to heat, humidity, vibration and other factors.

 Disadvantages of DLP Projector

  • Some viewers are bothered by the "rainbow effect" - particularly in older models .
  • Rear projection DLP TVs are not as thin as LCD or plasma flat-panel displays (although approximately comparable in weight), although some models as of 2008 are becoming wall-mountable.
  • Replacement of the lamp / light bulb in lamp based units. The average life span of a mercury lamp averages 2000–5000 hours and the replacement cost for these range from $99 – 350, depending on the brand and model. Newer generations' units use LEDs or lasers which effectively eliminate this issue, although replacement LED chips could potentially be required over the extended lifespan of the television set.
  • Some viewers find the high pitch whine of the color wheel to be an annoyance  though the drive system can be engineered to be silent and some projectors don't produce any audible color wheel noise.
  • Dithering noise may be noticeable, especially in dark image areas. Newer (post ~2004) chip generations have less noise than older ones.
  • Error-diffusion artifacts caused by averaging a shade over different pixels, since one pixel cannot render the shade exactly.
  • Response time in video games may be affected by upscaling lag. While all HDTVs have some lag when upscaling lower resolution input to their native resolution, DLPs are commonly reported to have longer delays. Newer consoles such as the  do not have this problem as long as they are connected with HD-capable cables.
  • Reduced viewing angle as compared to direct-view technologies such as CRT, plasma, and LCD
  • May use more electricity, and generate more heat, than competing technologies.
  • Some people may be able to observe a phenomenon in which the projected contents appear to be cycling through it colours for the duration of the presentation. This is most easily seen by using a camera's 'live view' mode on projected content.

                                         CRT PROJECTOR

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 (instead of a single, color CRT), and their own lenses to achieve color images. The redgreen 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 early 2000s.

Advantages of CRT projector

  • Long service life; CRT's maintain good brightness to 10,000 hours.
  • High-end CRT projectors can precisely display images up to 1920 x 1200 [3][4] 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 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 mechanisms.
  • Very fast response time (especially when compared to LCD-based projectors), resulting in minimal (if any) motion blur when showing video with fast motion.
  • CRT projectors do not show a Rainbow effect seen with single chip DLP projectors.
  • CRT projectors are both considerably larger and heavier than comparable LCD and DLP projectors.[5]
  • 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.

 Disadvantages of CRT projector

 CRT projectors are both considerably larger and heavier than comparable LCD and DLP projectors.[5]

  • 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

No courses in this category