Opaque projection is a method of enlarging and displaying nontransparent material on a screen, e.g. pages from books or magazines, maps, etc. It makes a wide range of visual materials available for group viewing. The opaque projector is used to project photographs, drawings, book pages and the like onto screen for group viewing. It performs this function by using a strong 1000 watt incandescent lamp to reflect light off the surface of the material. The image is reflected through a lens onto a screen. As the light is reflected off the material rather than passing through it, opaque projection is classed as an indirect projection system.
Indirect projection is less efficient than the direct projection process used for showing slides, filmstrips, motion picture film and overhead transparencies. Much of the light is absorbed by the material being projected, thus making the screen image dim. The room must be completely darkened to view the material properly.
Advantages:
- Materials such as pictures which lose much in reproduction processes can be viewed naturally.
- Colour can be projected.
- No special preparation of material is required.
- Relatively flat three dimensional objects such as coins, plant leaves, and insect specimens can be projected for group viewing.
- Prints, pictures, etc. can be viewed with minimum damage due to handling by numerous people.
- Student work such as drawings, solutions to math problems, compositions, etc. can be viewed and discussed by a group.
- Tracings and enlargements of printed or pictured materials can be made by projecting onto a blank sheet of paper.
Disadvantages:
- Dim image means the room must be almost completely dark.
- Machine is bulky, heavy, cumbersome to move.
- High wattage lamp generates a lot of heat, making parts of the projector unsafe to touch. The heat may also damage materials being projected if they are exposed too long. Laminated or plastic book covers can bubble or melt, and the glue on paperbound books may melt.
- Pictures must be flat or parts of the image will be out of focus.
Troubleshooting
Problem: No light after flipping switch
Solution: Be sure projector is securely plugged into an electrical outlet.
Check lamp. If burned out, replace it. Since you must push down very hard on the lamp while twisting it, be sure to use a cloth.
Switch may also be defective. If so, have a media technician replace it.
Problem: Line through picture
Solution: The piece of glass between the material and the lamp may be broken. Be sure to replace if with the manufacturer’s glass since this glass has special properties for resisting heat and pressure.
Problem: Glass is broken
Solution: Someone applied too much pressure when loading the material. The material should be snug in the projector – not tight.
Problem: Brown spot appears within projected image.
Solution: The material is beginning to burn. GET IT OUT!
Problem: Image won’t focus, even with lens out all the way.
Solution: Projector is too far from screen, move it closer, or material is not held flat, adjust the height of the platen.
Maintenance
Little maintenance is required.
Clean lens with a soft dry cloth.
Blow off foreign matter or dust if it gets on the mirror inside the projector.
The mirror scratches easily if touched.
Operating instructions
- Plug in.
- Place item to be shown on platen (stage). Place material face up with bottom edge toward screen.
- Use platen lever to raise and lower stage.
- Turn on projector with ON/OFF switch.
- Focus image.
- To enlarge image, move projector away from screen, to make smaller, move projector closer to screen.
- Warning! Because of the heat generated by the bulb, do not leave photos or other paper material on the platen area for too long.
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