Fisheries Extension Education (2+1)

2.8.1 Projected Visual Aids

Extension educator needs to know some basic things about the projection equipments since simple adjustments will often yield greatly improved pictures on the screens or improvements in the sound. Projected aids help for the effective transfer of the message from one source to another. However, the extension educator relates the effectiveness to the appropriate selection of the equipment.  

The principle involved in projection is that “when light falls on a transparent or translucent or opaque object, it passes through the object or is reflected by it; then if it is made to pass through a convex lens and allowed to fall on a screen at a convenient distance, an inverted image of the object will appear on the screen”. If the object is initially kept inverted before the source of light, the image will be straight and comprehensible.

There are three major projection systems:

1. Direct projection.

2. Indirect projection.

3. Reflected or opaque projection.

1. Direct projection

Direct projection is the most commonly used system. By this method, the light is passed directly from the projection bulb through the objective lens on to the screen. A minimum light is lost in this method. The most commonly used direct projection equipments are  slide projector, 8 mm/ 16 mm/ 35 mm motion picture projectors.

2. Indirect projection system

With an indirect light source and using mirrors, the projector can be used in front of the room. The materials being projected are placed on a flat platform above the light source. Although in some instances, there is a loss in the amount of light passing through an indirect projection system, as compared with direct system, the loss is negligible. The overhead projector works on this system of projection.

3. Reflected/Opaque projection system

Projection by reflection is used in the opaque projector. Materials which are flat or semi-flat materials can be used here. Opaque materials such as pictures, book pages, and objects can be projected. In the opaque projector, condenser lens are not used to spread the light evenly over the object being projected, instead a series of mirror surround the platen of the projector. The mirror reflects all possible light onto the object. The image is reflected in a large mirror placed immediately above the object through a large objective lens to the projection screen. The reflected system absorbs great deal of light, making it mandatory to use the opaque projector in a darkened room for the most satisfactory projection.