What are overhead projectors? Everything you need to know

There are many popular types of projectors, such as videos or slides. But have you ever heard of the overhead projectors? 

What is an overhead projector? How is it different from the other category? Should you purchase this device to upgrade your home theater system? 

If you are curious about this device’s functionalities and operating mechanism, don’t skip the information in the post. We will discuss the basics of overhead projectors and give you a detailed answer.

After reading this post, you can understand what an overhead projector means and make a wiser purchase decision. Now let’s move on to the definition. 

What Is An Overhead Projector? 

The overhead projector is the most basic type of projector. It is a reliable device that operates by projecting light through the lens to create the images on the projection display. 

Similar to the video or slide projectors, an overhead device projects the light to a large projection screen (wall or panel) for a large audience to see. It is ideal for the viewing distance of 2 to 4 meters from the screen. 

A complete overhead projector includes a large box that contains the cooling fan, an extended arm, and a bright light bulb. There is a small mirror that reflects and directs the light to the projection screen at the end of the extended arm.

The History Of Overhead Projectors

The overhead projectors used to be very popular in the past decades. Yet, the invention of more advanced devices has decreased its popularity and utility. 

The first recognized overhead projection was invented in 1853 by Edmond Becquerel, a French physicist. Back in the days of World War II, the military used the overhead projectors for servicemen training.

In the following years, this device quickly became prevalent in many classrooms and corporations after the war ended. The increasing demand for this device led to the founding of Buhl Industries in 1953. 

This corporation was the top producer of the optical refinements used in overhead projectors. The demand for these devices in education and industries still increases, even in the late 1990s and the contemporary era. 

Overhead Projector
The Overhead Projector

Optical system

Like a regular slide projector, an overhead projector operates with a focusing lens that directs and projects the light source onto the projection screen. 

To create a much larger image, there are basic differences in the optical system.

The transparency in this device is placed face up. There are also additional mirrors near the lens to direct the optical system. 

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The Main Components Of An Overhead Projector

A regular overhead projector consists of the following items:

  • The base: The most crucial part of the device, which contains the other components like the bulb, mirror, transparencies, and extended arms. 
  • The mirror and reflectors: This component helps reflect and direct the light from the lamp to the projection screen. They prevent the dim images resulting from light scattering. 
  • The cooling fan: The fan helps cool down the other components and prevents damage or overheating. It ensures that the device functions stably, especially the projector lamp. 
  • The Fresnel lens: It has a round design and is placed under the glass cover. The Fresnel lens helps adjust and direct the light rays from multiple spots into one certain place.
  • The extended arm: The main use of the arm is to stabilize and hold the projector head. This tool allows users to adjust the image on the projected display to get a better viewing experience. 
  • The projector head: The head consists of one mirror and an objective lens inside. It has an open bottom so that the light can get through, which is critical for image projection. 

If you want more detailed information, consider watching the video below. 

The Glass Mirror

Types Of Overhead Projectors 

There are three types of overhead projectors that use different optics. 

The first one is the direct optic projector with aligned optics and a light source, reflecting the light through the mirror to the projection display. 

The second type uses folded optics, which have a mirror in the middle of the lens and the light bulb. These devices can produce a clearer image quality and higher brightness, making them a more advanced option than direct optics. 

The last category uses reflected optics, which has the lens attached to a mirror.

When the light bulb projects the light to the lens, the mirror reflects and directs the light onto the projected display. 

This feature is prevalent on small-size and portable overhead projectors, which are very liable and easy to use. 

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Uses Of Overhead Projectors 

Before computer-based devices became popular, the device was very common in education and businesses due to its great utility. They are very cheap and easy to use, suitable for many people.

The content and teaching materials can be enlarged on the projection display for many students to see. It helps save time and effort when making use of the prepared teaching plastic sheets that contain the content of the lesson. 

People place the device in a comfortable place for the teacher to write and use. 

The Use Of Overhead Projector In Classroom

Do An Overhead Projector Have Disadvantages?

Despite their affordability, the overhead projectors are power-consuming as they require a constant electricity supply. They also produce a lot of heat in the operation process, which can lead to external damage and regular shutdowns. 

The cooling fans on overhead projectors generate a lot of noise, which can decrease your focus in the classroom and work. 

Lastly, they cannot produce videos or moving images, which is a major disadvantage compared to the more advanced types of projectors nowadays.

Final Thoughts 

Unlike modern devices, an overhead projector uses a sheet of plastic film called transparency. It can project written or printed images. They used to be very popular in education and business in the past. 

I hope that you can understand the basics of an overhead projector based on the information provided in this post. Thank you for reading!

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