What Is an Overhead Projector?

Garry Crystal

An overhead projector is a very basic but reliable tool used to display images onto a screen or wall. It consists of a large box containing a cooling fan and an extremely bright light, with a long arm extended above it. At the end of the arm is a mirror that catches and redirects the light towards the screen.

Projectors can be mounted to ceilings or used as mobile devices.
Projectors can be mounted to ceilings or used as mobile devices.

This type of projector can be used to enlarge images onto the screen or wall for audiences to view. Transparencies can be placed onto the base to be viewed by both the audience and the speaker. The device was once a common feature in both classrooms and business meetings, although it has seen a decline in use as more sophisticated computer based projectors are favored.

Overhead projectors usually project images onto a screen or wall.
Overhead projectors usually project images onto a screen or wall.

Overhead projectors were used during World War II as a tool to train groups of servicemen. In the 1950s and '60s, it crossed over into the classroom as an educational tool, and then into the business world as a training tool. It reached its sales peak in the 1990s, when almost every classroom and business place in America had one installed.

The projector is best used when the screen is approximately 6 to 12 feet (about 2 to 4 meters) from the projector. There are overheads that can increase the distance between projector and screen, but these are usually custom built and the cost is greatly increased. The biggest difference that can be seen between projectors is the type of optics used.

There are three main types of optics that can be used in the overhead projector. A direct optics projector puts the optics and light source in a straight line, allowing the image to be reflected from a mirror onto the screen. It's a very common form, and relatively inexpensive, but it can get quite hot.

Folded optics or chamber optics have a mirror placed in between the lamp and the lens, and a light source that is surrounded by an elliptical faceted reflector. This has a number of benefits, including making the resolution quite clear, and making more light available to project the image. This model is usually cooler than direct optic versions.

Another type is the reflected light optic, which has a specially designed lens that is backed by a mirror. The light source directs light to the lens and is reflected by the mirror. The reflected light is directed back through the lens and onto the main projective lens. The light is then focused to a second mirror and onto the screen.

The reflected light optic is used more in portable overhead projectors, and the cooling system, light source, and main projection optics are all placed in one unit. The entire projector can be folded down into a case for portability. Although still used in many classrooms around the world, these devices are on the decline. Some critics still favor them for their reliability, however, and claim that they are far easier to use than the more sophisticated digital versions.

Overhead projectors have been a staple in schools since their introduction in the 1930s. The tool was first developed and used in France in 1850, but it took several decades to arrive stateside and make an impact in education. When overhead projectors became a mainstay in classrooms, their utility in many other applications became apparent, too. Now, overhead projectors can be found in an array of settings, demonstrating just how useful this tool can be! Understanding the technology and common uses of this tool can help you harness its power.

Who Uses an Overhead Projector?

The aforementioned prevalence of overhead projectors in classrooms points to one of the tool’s most frequent users — teachers. Indeed, educators are one of the most frequent users of overhead projectors. This is due in large part to the obvious usefulness the tool offers for presentations and lessons taught in class. Rather than writing content on the board and unnecessarily expending valuable teaching time, a teacher can simply use an overhead projector to display a lesson easily to the whole class. Other professionals benefit from the use of overhead projectors, too, including business personnel, movie theater managers, artists, and many others.

Overhead Projector Technology

Overhead projectors function by illuminating an image with light, enlarging it, and projecting it onto a screen or blank surface. This process is made possible through the application of several mechanisms — a converging lens, a mirror, and a transparency sheet. The converging lens bends the light in a way that directs it towards the screen. The mirror flips the image of the transparency so that it is projected the right way. Finally, the transparency sheet represents the image that is projected onto the screen.

This technology remained relatively consistent from the emergence of the overhead projector until its decline in popularity. This decline happened around the late 1980s and early 90s as digital projectors were invented and gradually replaced the technology of the original overhead projector. Though their technology is different, digital projectors are often still called “overhead projectors” because they can be mounted overhead and they are projectors.

Finding the Right Overhead Projector

Finding the right overhead projector is important if you plan on giving a presentation or teaching a class that will require the use of visuals for a big group. An overhead projector will make this part of the job easier and allow you to easily share your text or visual with everybody attending. Of course, in order to do so, you will need to find the right overhead project for the job — and this can be a challenge if you don’t know what to look for.

You can start by narrowing down what kind of overhead projector you want. Modern technology has made an array of options available, including the following:

Do your research before deciding which option to opt for, and be sure that it’s compatible with the type of presentation you plan to give. BE sure that you select the correct type of lens and light, too, for the best quality projection.

How to Use an Overhead Projector

Using an overhead projector is simple if you’re an experienced projectionist — but even if you aren’t, it’s easy to learn. Depending on the type of projector you’re working with, the exact operation will vary, but generally you can set it up by mounting it to a secured mount on the ceiling, powering it on, and selecting your input source. You should then be able to project an image or text onto a screen.

In addition to the obvious uses for presentations and teaching, there are an array of creative uses that you can use an overhead projector for, too. Getting creative is a great way to get the most out of your overhead projector. Some ideas potential creative applications include the following:

  • Create art projects by projecting a surface that can be drawn upon
  • Project a movie or video game that can be played in real-time
  • Create a scenic background for photoshoots and creative projects

Any of these projects can open the door to creative expression for kids and adults alike. Remember that when you’re using your overhead projector, you should follow all safety protocols outlined in the manual so that everybody is safe while it is in use. Be careful not to tilt the projector excessively, and don’t look directly into the lens while it is powered on. Regularly clean dust out of a projector, too, to prevent a fire hazard.

Overhead projectors were once a common feature in both classrooms and business meetings, although it has seen a decline in use as more sophisticated computer based projectors are favored.
Overhead projectors were once a common feature in both classrooms and business meetings, although it has seen a decline in use as more sophisticated computer based projectors are favored.

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Discussion Comments

anon997276

Anon 57653 You are looking for an Opaque Projector.

anon357857

I love how I can just understand everything the way it's explained. Thanks a million!

anon72537

I thought this helped so much. I love WiseGeek because this is where I get all my information for projects on. Thank you so much WiseGeek! I didn't know that you could become a member, but I guess I'm not a WiseGeek after all. LOL (Pun intended)

Love, Jessalhermione (for real)

anon57653

I was actually looking for something that would project and to enlarge an image (not from a transparency) but from a photo, signwriters used them and probably still do. I just thought they were called enlargers. where can I find one ?

malena

i think this is also in some places referred to as an over projector.

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