Too much information about: Overheads
Overhead Projectors. What can we say about the workhorse of the AV world? Long suffering, frequently misused and always underappreciated. We'd like to rectify that with this tribute to the Overhead Projector.
We have three types of Overheads:
The Stage Overhead
is the large, free standing unit with the power cord hidden in the
base. The light source is in the base and shines up through the transparency
and is reflected out the head lens to the screen.
Pluses: Better imaging, spare bulb, color correction.
Minuses: Heavy and cumbersome. You'll need a cart to transport. Also has a fan to cool the bulb (but it's not too noisy).
The Portable Overhead
folds down and has a cover. The light source is in the head of the
unit. It works by shining the light down through the transparency
where it is reflected off the base back up to the head where it is
focused with a lens and a mirror to bounce the image to the screen.
Pluses: Better imaging, spare bulb, lightweight, no fan.
Minuses: None that we can think of.
The Briefcase Overhead
folds down into a case about the size of a briefcase. The top of
the case doubles as a reflective surface and it works like the Portable
Minuses: No spare bulb, gets hot, the base plate must be seated properly or the image won't look right.
The Stage and Portable Overheads are pretty self-explanatory and trouble free.
However, the Briefcase Overhead needs a few tips. Since a picture is worth a thousand words...
Set-up: An overhead should be set up on the table at the front of the classroom. We do not recommend using a classroom desk, because the top is tilted back slightly and the overhead will slide off. (Really, it happens more times then you might think.)
Power Sources: When you check out your classroom before the semester starts, locate the closest power outlet to the front of the room. NOTE: not all classrooms have a power outlet at the exact center front of the room. Most overhead power cords are six feet long or LESS. Ask for an extension cord to prevent what is called "clotheslining" (where the cord is stretched off the floor like a clothesline) or having to place the projector so close to the screen the image is too small to see.
Distance from the Screen: About 6 feet or so (which makes an extension cord a necessity) to get an image large enough for those students who try to hide in the back of the room.
Angle to the Screen: Must be at right angles. If you try to set it up at any other angle, you get an image that is too wide on one side. Also, use the mirror in the head to tilt the image up and down and the focus knob to sharpen the image. Try not to tilt the image too far up or the image will "keystone" which means the top is much larger than the bottom and the image will be distorted.
A Word About Transparencies:
When creating your transparencies, remember these tips:
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