Overhead Projectors

Looking for an easy way to share your presentation with an audience or a useful tool in classroom learning? Overhead projectors remain one of the most popular presentation accessories. Although they are increasingly being replaced by computer monitors and LCD projectors, critics feel that these newer systems are more expensive, more prone to failure, and have a steeper learning curve than the traditional overhead projector. Consider purchasing an easy-to-use overhead projector instead.

Contents [Hide] 1 Opaque vs. Overhead Projectors 2 Features of Overhead Projectors     2.1 Lens Type     2.2 Brightness (Lumens)     2.3 Lamp Life     2.4 Innovation 3 Overhead Projector Configurations

Opaque vs. Overhead Projectors

The first projector used as a presentation device was not the overhead but the opaque projector.

• Opaque Projectors

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 screen. Opaque projectors require brighter lamps and larger lenses than overhead projectors. Care must also be taken that the materials are not damaged by the heat generated by the light source.

• Overhead Projectors

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. A mirror, on a long and folding arm, redirects the light forward instead of up. The mirror allows both the presenter and the audience to see the image at the same time, with the presenter looking down at the sheet of paper and the audience viewing the screen.

Features of Overhead Projectors

Lens Type

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

Brightness (Lumens)

Each overhead projector is rated on brightness by a term called the "lumens." For rooms where the ambient light can be lowered, the standard 2,000 lumens will suffice. When you are projecting in a room where ambient light is significant or when you are looking to project complex images (namely images with 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 offers the longest lamp life.  Other lamp types (FXL, EHA, ENG) with higher lumens offer shorter lamp lives.

Innovation

The industry pioneer 3M has been responsible for many of the major advances in projector technology, making their overhead projectors some of the most popular in the market. In recent years, however, projectors such as Buhl have gained some advantages over 3M. Their projectors offer amenities such as 360 degree rotating heads, double fesnel lenses (good quality), ambidextrous operation, and auto lamp changers.

Overhead Projector Configurations

Although most overhead projectors are used for displaying images in rooms where the distance from the projector to the screen is 6-12 feet (the "throw distance"), some projectors are specialty-made to go beyond this range.

For the most part, however, overhead projectors can be found in the following optical designs:

Overhead Direct Optics Projector  The most common kind of overhead projector, with the lowest cost. The lamps are usually two pre-focused Halogen lamps. The surface mirror on the projection head can be articulated to better direct the image.

Overhead Chamber Optics Projector  Also known as a "Folded Optics" projector. Superior light collection; a 50% increase versus similarly powered direct optics units. Improved resolution. Stylish housing design - more user friendly for use and maintenance. Better cooling. Slightly higher cost (due to the extra components and specialized lamp).

Overhead Reflected Optics Projector  More portable - the assembly has a mechanical release device allowing the entire unit to break down into a slim profile. Easy transport - carrying case provided. Double imaging can be a problem. Reduced resolution and light output. Slightly higher cost (due to the extra components and specialized lamp).

Don't forget, you'll also need a projector screen  for optimal viewing.