The Overhead Projector (Ohp)

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  • Topic: Overhead projector, Opaque projector, Slide projector
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The Overhead Projector (OHP)

August 24, 2012


Overhead Projectors are still being used in a lot of schools, like in the Philippines. It is not as modern as other equipments, but it still serves its purpose which is to show enlarged images on screen.

I. Description

The Overhead Projector is an optical device for showing images on screen, usually for group viewing. The OHP is mainly used for projecting charts, sketches, and other material prepared on sheets of transparent plastic.

II. Techniques

• You can show pictures and diagrams, using a pointer on the transparency to direct attention to a detail. The silhouette of your pointer will show in motion on the screen.

• You can use a felt paper or wax-based pencil to add details or to make points on the transparency during projection.

• You can control the rate of presenting information by covering a transparency with a sheet of paper or cardboard (opaque material) and then exposing data as you are ready to discuss each point. This is known as the Progressive Disclosure Technique.

• You can superimpose additional transparency sheets as overlays on a base transparency so as to separate processes and complex ideas into elements and present them in step-by-step order.

• You can show three-dimensional objects from the stage of the projector-in silhouette if the object is opaque or in color if an object is made of transparent color plastic.

• You can move overlays back and forth across the base in order to rearrange elements of diagrams or problems.

• For special purpose, you can simulate motion on parts of a transparency by using the effects of polarized light.

• You can simultaneously project on an adjacent screen other visual materials, usually slides or motion pictures, which illustrate or apply the generalization shown on a transparency.

Other reminders on the effective use of the OHP are:

• Stand off to one side of the OHP while you face the students.

• Don’t talk on the screen. Face the students when you talk, not the screen.

• Place the OHP to your right, if you are right handed, and to your left if you are left handed.

• Place the OHP on a table low enough so that it does not block you or the screen.

• Have the top of the screen tilted forward towards the OHP to prevent the “keystone effect” (where the top of the screen is larger than the bottom).

• Avoid the mistake of including too much detail on each image. A simple layout makes an effective slide. If an audience needs to be given details, provide handouts to be studied later.

• Avoid large tables of figures. Come up with graphic presentations.

• Don’t read the text on your slide. Your audience can read.

• Avoid too much text. Rely sparingly on printed text. Come up with more graphs, diagrams, or pictures.

• Your presentation must be readable from afar.

• Simple use of color can add effective emphasis.

III. Advantages

• The projector itself is simple to operate.

• The OHP is used in the front of the room by the instructor who has complete control of the sequence, timing, and manipulation of this material.

• Facing his class and observing student reactions, the instructor can guide his audience, control its attention, and regulate the flow of information in the presentation.

• The projected image behind the instructor can be as large as necessary for all in the audience to see; it is clear and bright, even in fairly well-lighted rooms.

• Since the transparency, as it is placed on the projector, is seen by the instructor exactly as students see it on the screen, he may point, write, or otherwise make indications upon it to facilitate communication.

• The stage (projection surface) of the projector is large (10 by 10...
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