Relation of Screen Siie and Viewing Area. Since the size of the viewing urea is a function of the unage width, it follows that the proper screen size for any given space will be determined by the number of viewers intended. Conversely, a given type and size of screen automatically establishes the size of the viewing area, and consequently the size ol audience that can be properly accommodated The viewing area is the pattern which determines the seating arrangement in any learning space where projected images are to be used, and in the larger spaces, at least, it also in fluences the shape of the roam, (Fig 11)
Planning the Projection System Steps in Design. Whether front or rear projection is to be used, the design of the projection system itself involves determining:
1 The size of viewing area required
2. The appropriate screen size
3. The proper type of screen
4 The appropriate projector(s) — the required lumen output, focal length and location
5. The maximum permissible level of ambient fighting on the screen.
Trial and Error at First. The desired audience size is usually predetermined. In some cases, the size of the viewing area, too. may be established by existing conditions. Otherwise, its size and shape should be tentatively
approximated in accord with Ihe principles already discussed. Because of the relationship between its dimensions and the width of screen to be used, the inexperienced designer necessarily proceeds by trial and error until he arrives at a satisfactory arrangement accommodating Ihe specified audience in proper relationship with the screen. Sometimes, the problem may be reversed, requiring a determination of the optimum audience and seating arrangement for projection equipment already at hand
Standards Professional standards accepted by the Society of Molion Picture and Television Engineers have been developed for viewing front and rear projected images These standards provide excellent imeges. However, for the purpose of economy in classroom use ol projected media, it is felt that some standards based on the poorest seat in the room can be lowered, particularly for gross images The following resume ol standards indicates by asterisk (*) those that are less than the professional standards.
Screen Brightness Motion pictures:
5 ft L —Minimum* (gross images) 10 ft L— Satisfactory 1 5 ft L — Excellent
20 ft L - Maximum (flicker threshold for some observers)
5 ft L— Minimum for slides with detail 10 ft L— Satisfactory 20 H L Excellent
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