es

Overhead Projectors

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 6made to go beyond this range. For the most part, however, overhead projectors can be found in the following optical designs: Don't forget, you'll also need a '''projector screen''' for optimal viewing.