Principles and Techniques of Veterinary and AH Extension

Handling and Use of Overhead Projector

EXERCISE-2: HANDLING AND USE OF OVERHEAD PROJECTOR AND SLIDE PROJECTOR

• Overhead projector projects any transparent instructional item such as charts, graphs, drawings, pictures etc., on to the screen.

Aim

• To promote group understanding of the information material.
• To create effectiveness where the chalk board technique is ineffective.
• To show the facts and figures clearly and in an effective way.

Principle

• Overhead projectors function under the principle of indirect projection.

• Rays of light come from a projection lamp, enter one element of the condenser lens unit and are reflected by a plane mirror placed at an angle of 45 degree with either of the axis of the condenser unit. The reflected rays enter the other element of the condenser unit, pass through the slide or transparencies, enter the objective lens and are again reflected by another plane mirror placed at an angle of 45 degree with the axis of the objective lens to form an enlarged image of the material on the screen. The loss of light is more when compared to direct projection.

Materials required

Transparent sheets

• Variety of transparent materials can be used
  • Acetate sheet
  • Cellophane paper
  • Used x-ray films
  • Glasses
• Subject matter
• Writing pens:
  • Any pens having transparent colours can be used. Specially manufactured OHP pens are available. These are of 2 types viz. oil based and water based. Even glass marking pencils and crayons can be used.
• Overhead Projector