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Overhead Projectors
The overhead projector is a versatile tool that can be used in either normal or dimmed lighting. When used simply with a marker and a blank transparency, a projector serves some of the same functions as a chalkboard, but with several advantages. An overhead can adequately project in large classrooms. Like a chalkboard, it can be used to record student responses to an open question as a way of focusing the discussion, but as an added feature, a transparency allows you to save such responses, either for your own use or to display again in a later class period. It also allows you to face the students while presenting the content.Perhaps the real advantage of overheads, however, is the ability to prepare transparencies in advance. With computers and laser printers and software such as PowerPoint (which comes with ready-to-use templates), it is easy to produce quality transparencies that can display more than just text. Davis (1993) suggests that overheads can be used to present the day’s outline; difficult names or terminology; diagrams, charts, maps, graphs, drawings, or other illustrations; chronologies of important dates; formulas, theorems, computations, or steps in mathematical proofs; and major points of lecture. Cartoons are an excellent way of simplifying complex ideas and adding humor. With a little effort, spatial, statistical, and structural relationships can all be visualized on an overhead. Overlaying several transparencies allows you to illustrate changes, processes, or alternatives.
With all these possibilities, the temptation is to put too much on the overhead, so it is important to limit the amount of information on each page. Overheads are not a good means, for example, of displaying an entire page of a book. Use at least an 18-point font size and plenty of white space to make your transparency less cluttered and easy to read. An instructor should keep in mind visibility from the back row, since students often will not speak up to say that type is too small. Highlighted outlines with clearly defined headings work particularly well, and color can be used to create emphasis.
During presentation, it is particularly helpful if the instructor covers up the sections that are yet to be introduced and displays only the content being discussed. This technique, called progressive disclosure, can help students follow the instructor’s train of thought, concentrate on what is being discussed, and avoid becoming distracted. For similar reasons, it is best to turn off the projector altogether when it is not being used or directly referred to.
Instructors should also be aware that standing in front of the screen may block students’ view and thus work against one of the advantages of the technology, i.e., the ability of the instructor to face the class when writing and pointing to the text material. Therefore, it is very helpful to stand to the side during the presentation.
Some Ohio State instructors have offered these additional tips for using overhead projectors:
- Know how to replace an overhead bulb and where to get a replacement.
- Keep extra overhead pens handy.
- Use no more than 10-12 transparencies in a 50-minute lecture class.
- Wait briefly before speaking after you put up a new transparency.
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