We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
A
Types of Visual Aids and Their Uses 1 25
In the case of the opaque screen, the projector is usually placed toward the back of the classroom with the screen hanging in the front of the room. The required distance from the screen to the projector will be determined by the size of the screen and the focal length of the lens used.* Ordinarily the classroom screen is from 3x4 feet in size to 6x8 feet in size, and any screen within the limitations of those dimensions will be reasonably satisfactory. Too large a screen should not be used as it will have a tendency to tire the eyes of those who may be obliged to sit close to it. At the same time, the screen
should be large enough to provide a clear / \
picture when viewed from the back of the
_ f Photo Courtesy Society for
room. Une of the rules of long standing among Visual Education, inc.
theaters is that the width of the screen should Tripod Projection Screen
be approximately one-fifth the distance from
the screen to the person in the audience farthest away from it. In other
words, if a screen is being selected for use in classrooms approximately
twenty-five feet from front to back, a screen five feet wide would be
desirable.
Beaded Screens. The beaded screens which have been developed within the past few years, and which are used extensively in schools, are similar to other screens except that the surface is covered with small glass beads. This type of screen has the highest direct reflective qualities of the three general types — beaded, silver, and mat-white — but the picture when viewed from various angles in the room is not entirely satisfactory. If a beaded screen is to be used at one end of a long narrow room it will be entirely satisfactory. On the other hand, if it is to be used on one side of a short or square room, those who are seated at wide angles from it will receive a poor reflection of the picture. Tests which have been conducted by the Electrical Testing Laboratories in New York City indicate that the beaded screen gives
*Screen image tables for single and double frame filmslides, 16 mm. motion pictures, and lantern slides will be found on pages 226 and 227.