Overhead projectors has replaced the need of a chalk box and the black board which needs to be cleaned manually everyday. Instead of writing on the boards presenters feel more comfortable to present through the overhead projectors and instead of improving the handwritings they prefer to improve the communication and the presentation skills. Therefore overhead projectors provide an easy access to a successful presentation.

Introduction

Who invented the overhead projector? The first overhead projector was invented by Suaing Chong from China and was used for the police identification work. Its use increased when the US Army planned to use it for training purposes in the II World War 1945. But its use keeps on increasing in institutions and the businesses in the late 1950s and the early 1960s. 3M Overhead Projectors are famous because in the early period 3M Company was the major manufacturer of the Overhead Projectors. But nowadays 3M, Buhl and Apollo Overhead projectors are widely used.

Construction

Overhead Projector Parts consists of a large box which contains an Overhead Projector Lamp or overhead projector bulbs bulb and a fan to cool it. A Fresnel lens is present on the Top of the box. Above the box there is another lens and a mirror. The lens controls the path of the light while mirror controls the display of the image both for the presenter and the audience.

Uses

Overhead projectors are used to display images. But it requires special techniques for its installation. The distance between the Overhead Projectors and the Overhead Projector screens is supposed to be 6 to 12 feet that is called the projection distance or the thrown distance. But the distance beyond that requires special installation techniques. Nowadays LCD panel for overhead projector are in demand but they are expensive therefore overhead projector rentals are also available in market at different rates.

Performance Versus Cost

Overhead Projectors are available in different optical configurations and prices depending on performance. They are available in three optical designs which are as follows:

Folded Optics/ Chamber Optics

This optical design interposes the surface mirror between the light and the Fresnel lens. It is the most specialized optical design and the most costly Overhead Projector because of the following reasons:

• An expensive lens is used in it
  
• Improved resolution
  
• It is user friendly in terms of its use and maintenance
  
• It has superior light collection
  
• It reduces the temperature when a transparency is projected because it uses a reflector lamp that uses a Diachronic coating which transfers the heat
  

Direct Optics

This Overhead Projector is designed in such a way that light source and the associated optics are positioned in the straight line that is called the optical axis. The Overhead Projector lamps for this design are usually two pin halogen lamps. The power requirement for this Overhead Projector is from 250 to 600 watts.
This Overhead Projector is the lowest cost projector for a number of users.

Reflected Optics

This Overhead Projector is famous for its portability because in this Overhead Projector the light source, cooling device and the projection optics are configured in a single unit which makes it a Thin Overhead Projector. It is significant because of easy carriage but at the same time it sacrifices the resolution, reduces the light output and increases the chances of doubling the image.

Advantages Of Overhead Projectors


It has following advantages:

• It provides a direct interaction of presenter with audience
  
• Provides easy material access to the speaker and audience
  
• The transparencies can be used many times
  
• The sequence of the presentation can be changed according to the point of discussion
  

To build an Overhead projector following things should be kept in mind:

• It should be low enough so that it does not block the speaker on the screen
  
• Overhead Projector Screen should be placed diagonal to make a clear view for the audience
  
• It should be placed on the left for the left handed and vise versa