Projecting Ideas On The Overhead Projector (1960)

The overhead projector has proved to be an effective visual aid to learning in many teaching situations in business and industry in the military and in highter is due largely to its effective use of good teaching techniques in class situations. s. It enlarges the material on the screen so that everyone in the class is able to read it easily. Normal room lights can be left on when the projector is in use, making it easier for the students to take notes. During the presentation, the instructor is able to remain in the front of the room facing the class. Because he also serves as the projectionist, he can control the rate of development of the material and can vary the presentation both orally and visually. Age of the projector turns on the light and focuses the lens by turning the focusing knob. This schematized diagram shows how the image of the material is projected onto the screen. The light leaving the projector bulb is reflected by a mirror and passes through the materials on the horizontal stage. It then passes through the focusing lens and is reflected by another mirror onto the screen. When the projector is used in the center of the room with the picture elevated on the screen, some distortion known as keystoning may occur. This can be corrected by tilting the screen until the picture assumes a normal appearance. Again, a similar effect is caused by projecting from the side of the room. For illustration purposes, we shall lower the image on the screen to eliminate any distortion. The type of materials to be used on the overhead projector may be either transparent, translucent, or opaque in nature. Transparent acetate is available in clear sheets and in a variety of colors. Frosted acetate is a good translucent medium. Materials such as a piece of writing paper are opaque and will not transmit light. Many types of presentations can be made using all three types of materials. They may be prepared before class begins or they may be developed by the instructor as he teaches. For instance, a theme which has been typed on a specially coated sheet can be placed on the stage for examination and discussion. Transparent plastic or acetate may be laid on top of the theme to avoid marking directly on the material. A China marking type of pencil produces a good opaque image for this purpose. Errors are easily erased with a dry cloth. A copy of the material on clear acetate will provide even more contrast in the projected image. Colored drawings are often used effectively to create interest in the presentation. The drawings may be as elaborate or as simply done as time and ability permit. Colored pencils, crayons, and plastic base inks may be used for these drawings depending upon the instructor's preference. Clear acetate is the best medium for use with ink. Materials developed during class should be simple in form and as easy as possible to read and understand. The use of color helps to unify various sections of the drawing and adds to its attractiveness as well. Crayons and colored pencils show up well when used on specially treated translucent sheets. Clear acetate is also available in rolls. When installed on the projector, the roll may be used for an entire presentation or for several presentations. The material may be developed in two ways. For example, it may be written by the instructor as he lectures, adding spontaneity to the presentation. If a great deal of material is to be presented, previously prepared information may be included as well. In this way, the role reduces the time needed for writing during class and allows the instructor to present more material in a shorter length of time. When completed, the material may be rolled ahead. The normal black and white relationship of the projected image may be reversed by the use of a carboncoated plastic sheet. As the stylus is drawn across the sheet, it removes the carbon and produces a white tracing. This technique often lends a very dramatic quality to the presentation. The white images produced in this manner show up well when projected on a chalkboard. In this case, a grid work is used as a guide for making graphs. If a mistake is made, the chalk can be erased without disturbing the grid. This is an example of the versatility of the projector when it is used in conjunction with other teaching aids. X-ray films are a type of black and white transparency and may be projected. Enlarging the image for group showings greatly facilitates the presentation of this type of information. Variety and interest can be added to a presentation on the projector through the use of opaque materials. In this illustration, construction paper was used for making silhouettes of Civil War caps and cannons to represent opposing sides in a battle. By moving them around, the progress of the battle can be shown. Colored acetate is used for accent. A colored sheet contributes to the mood and interest of the entire transparency. Distinctions in color as well as in the shape of the cutout models are often helpful. Maneuverability is one of the advantages of this technique. Contrasting color adds emphasis when needed. The overlay technique is an interesting way to present material. This type of transparency generally consists of a basic drawing and several clear acetate sheets. Each of the sheets contains additional drawings which when laid on top of the basic drawing add to the development of the illustration. Color helps to isolate and emphasize the area of discussion. While some transparencies may use only two or three overlays, others may use as many as six or eight. And as is true of most materials used on the projector, the instructor may control the rate of development to suit his delivery. A particular advantage of the overlay technique is that entire sections of the drawing may be removed or replaced for review or contrast as the instructor desires. Many demonstrations may be performed on the overhead projector. These are Polaroid filters. When pressure is applied to materials such as plexiglass, the polarized light reveals the stress marks within the material. In this way, one demonstration may be performed so that the entire class can observe it at the same time rather than having to repeat it for a number of groups. Another application of polarized light involves this motor-driven Polaroid disc which is placed over the projector lens. The disc is used in combination with strips of polarized tape which are placed on the acetate sheet of an overlay. When the disc rotates, the drawing is not affected. But when the polarized tape covers the drawing, the appearance of movement is obtained. The tape may also be placed so that the movement appears to be in the opposite direction. Devices such as this transparent slide rule have been designed to help the instructor present specialized information. The problem is written on an acetate sheet. The convenient size of the rule makes it easy for the instructor to manipulate the device. The most important feature of the rule of course is that it functions exactly as a standard slide rule does and simple operations can be performed using its scales. An example of a more complex device is this working model of a signal generator. Here, many parts are seen functioning at the same time. The relationship of the parts and their movements can be more easily explained and discussed because the instructor is able to repeat the cycle as often as necessary. Even chemical reactions can be shown on the overhead projector by shining a light through the side of a test tube and reflecting the image from a mirror through the projector lens onto the screen. The vertical view of a reaction can be observed. Many other interesting demonstrations can be shown on the projector when the instructor stops to consider the possibilities. Transparencies may be projected onto a sheet or piece of muslin for backgrounds for plays. The actors may perform in front of the setting or behind it if a shadow effect is desired. The following sequence is a visual interpretation of a ballet using transparencies. The artist has skillfully used transparent, translucent, and opaque materials to augment his impressions. Heat. Heat. [music] [music] [music] >> [music] >> Heat. Heat. [music] >> [music] [music] [music] [music] >> There are many ways to teach with the overhead projector. The progressive instructor will find that it is truly a versatile and effective aid to learning. Heat. Heat. [music] [music] [music] [bell]