Over the past 25 years I have had the unique opportunity to talk directly with many of the professionals and instructors who use Overhead Projectors as an integral part of their profession. Through these interactions I have accumulated notes and information that has inspired me to write these articles that pertain to some of the most common problems experienced by owners of today's and yesterday's Overhead Projectors. This is the eighth article in a series of articles that will be written from a professional Electronics Technicians point of view in regards to some of today's most common Overhead Projector problems and questions

There is a lot of confusion with end users of Overhead Projectors in regards to what type of focus head their Overhead Projector has, whether or not this was properly explained to them when they made their purchase, or if it really wasn't even an issue when they made their purchase. Yet when it comes time to purchasing replacement parts for the focus head of their projector, it will be vital information them to have an understanding, so that they are sure to purchase the correct parts.

Starting with the basics, there are two types of focus heads for Overhead Projectors and they are as follows:

An Open Head Overhead Projector allows the user to be able to touch the internal components of the head assy. In most cases the Reflective Front Surface Mirror is hinged and allows the user to flip it up or down.

A Closed Head Overhead Projector does not allow the user access to the front surface mirror of the head assy. It usually consists of a shell as

The focus head usually consists of three main parts:

Entrance Lens: This is the lens that the light shines up trough from the bottom of the projector.

Exit Lens: This is the lens that the light shines out of and on to the wall where you are projecting your image. There would be no Exit Lens in the case of an open head Overhead Projector, only an entrance lens.

Front Surface Mirror: This is what reflects the light (your image) from the base through the exit lens on to wall or screen you are projecting to.

When ordering parts for the focus head of your Favorite Overhead Projector this information will be invaluable to both you and the Service and Parts Technician who is helping you to determine exactly what parts you will need to repair your Overhead Projector.