Overhead Projectors

By AudioMan Updated on Thursday, January 14, 2016

Features to Consider Before Purchasing an Overhead Projector

Overhead projectors combine an old technology with new technology options to create machines which are both reliable and versatile. Available Buhl and 3M overhead projectors give you a wide range of choices to supplement almost any presentation. The question is which overhead projector is right for you?

To help you decide we put some of the best in class to the test. Let’s start with an explanation of what overhead projectors are and what overhead projectors do.

What are Overhead Projectors?

Simply stated, an overhead projector displays images to an audience. Overhead projectors typically consist of a large box containing a very bright light-source, a fan for cooling the box, and a large lens that focuses the light. Above the box, typically on a long and folding arm, is a mirror that redirects the light forward instead of up. Page sized sheets of transparent film are placed on top of the lens for display. The light from the lamp travels though the transparency and into the mirror where it is reflected onto a viewing screen. The mirror allows both the presenter and the audience to see the image at the same time, with the presenter looking down as if writing and the audience viewing the screen.

Overhead projectors were once a common fixture in most classrooms and business meetings. Increasingly overhead projectors are being replaced by larger computer monitors or LCD projectors. Critics feel that these newer systems are more expensive, much more prone to failure and have a steeper learning curve than the traditional overhead projector. As a result the overhead projector continues to be a popular presentation accessory.

The History of Overhead Projectors

The first projector used as a presentation device was not the overhead but the opaque projector. The opaque projector displays non-transparent materials by shining a bright lamp onto the object from above. A system of mirrors, prisms and/or lenses is used to focus an image of the subject onto a viewing screen. Opaque projectors require brighter lamps and larger lenses than overhead projectors. Moreover, care must be taken that the materials are not damaged by the heat generated by the light source. Suitable objects for display and projection include book pages, drawings, mineral specimens, leaves, etc.

In the early and mid 20th century, opaque projectors were produced as low cost toys for children. They were also marketed as an artist’s enlargement tool to allow images to be transferred to a prepared canvas. Eventually they came into widespread use for lectures and presentations. In its modern incarnation the Mark IV Opus Opaque Projector by Buhl still has a loyal following. For the most part, however, there is greater demand for overhead projectors than opaque projectors in the modern market.

Features of Overhead Projector

All overhead projectors share standard features which should be considered as the basis for your purchasing decision. The most important are lens type, brightness (lumens), lamp life and of course, price. Let’s consider how these features can be measured and compared, as well as one additional variable which I will call innovation.

Lens Type:

The most significant factor in overhead projection image quality is the type of lens being used. We offer projectors that feature the three most common lens types: singlet, doublet, and triplet. Image quality increases as you progress from the basic singlet lens type, to the advanced triplet lens type, though price generally increases, as well.

Brightness (Lumens):

Each overhead projector is rated on brightness by “lumens typical.” For rooms where the ambient light can be lowered, the standard 2000 lumens will suffice. When you are projecting in a room where ambient light is significant or when projecting complex images (including color), 2,500 lumens or greater is recommended.

Lamp Life:

Each overhead projector has an estimated lamp life that is primarily determined by the rating in lumens and lamp type. The common ENX lamp type, for example, offers the longest lamp life while the higher lumens and more specialized nature of other lamp types (FXL, EHA, ENG) offer shorter lamp lives.
In the case of Buhl, we have found that some newer and more innovative features have given them them a decisive edge over 3M and other manufacturers.


As an industry pioneer, 3M has been responsible for many of the major advances in projector technology. In recent years, Buhl has siezed the initiative and successfully innovated new features like 360 degree rotating heads, double fresnel lenses, rack and pinion focusing, ambidextrous operation, auto lamp changers, and Hi-Lo switching. As some of these innovations are patented Buhl has gained an advantage in innovation over 3M.

If you have questions about this or wish further advice on overhead projectors or other AV equipment please call us at 1-800-263-0112Ā or email us.