Most machines have a large, circular button on the front for this purpose, but on/off switch locations can vary. Alternatively, a transparency can be fed into a laser printer, and information from programs such as spreadsheets and databases can be directly printed on the transparency. Transparencies can be written on directly with a wet erase overhead pen. Place an overhead transparency on top of the flat glass surface of the projector. Make sure the overhead projector is plugged into a reliable power source. Situate the overhead projector on a low table that is 2 to 3 feet off the floor. A negative to LCD/DLP technology is the warm up time required for arc lamps.
A modern LCD or DLP uses an arc lamp which has a higher luminous efficacy and lasts for thousands of hours. Further, the intense heat usually causes the halogen lamp to fail quickly, often lasting less than 100 hours before failing and requiring replacement. A high-flow blower is required to keep the bulb from melting itself due to the heat output. Most overheads use an extremely high-power halogen lamp that may consume up to *750 watts yet produces a fairly dim, yellowed image. The lamp technology of an overhead projector is typically very simple compared to a modern LCD or DLP video projector. Turning the adjustment wheel moves the lamp to correct the focal distance and restores the all-white projected image. 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 colour fringing around the outside edge of the screen. Focal Length Adjustmentīetter-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. 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. 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 light from the lamp travels through the transparency and into the mirror where it is shone forward onto a screen for display. Transparencies are placed on top of the lens for display. Above the box, typically on a long arm, is a mirror and lens that focusses and redirects the light forward instead of up. On top of the box is a large fresnel lens that collimates the light. Cover your overhead projector when not in use because it can collect dust easily and affect the focus of your images, as well as clog the cooling fan.An overhead projector typically consists of a large box containing a very bright lamp and a fan to cool it.
Do not turn on and off the overhead projector simultaneously or you risk blowing the small lamp in your projector.This will enable you to place the projector back in the exact spot as before. If you have to store away your projector before you have completed tracing your image, you can mark the area on the floor where the table or chair legs stood with painters tape or a marker.That way you can easily move the projector forward or back as you adjust the size of your image. It is better to have the room dimly lit, and the overhead projector sitting on a small table or chair.To trace and outline your projected image on to your paintable surface. A canvas, wall, or any paintable surface to project your image on to.
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