Overhead Projectors

Rishav

An overhead projector is a simple and reliable form of a projector. Overhead projectors are used to project images or written material onto a wall or screen. Overhead projectors were
first created and used
Vega_Quadra_250YLS_OHP_Overhead_Projector.jpg
This is an image of a basic overhead projector made by the company M3; M3 is one of the biggest manufacturers of overhead projectors.
by the US army in 1945 during World War II. Then, in the the late 1950s and early 1960s, schools and business had access to overhead projectors.Though,
overhead projectors are old technology, they can still be found and used in most elementary/high school classrooms. It is in the 1990s, when overhead projectors were most popular,
as they were in almost every school in the United States. Transparencies are placed on the overhead projector so that both the audience and the speaker can see what is being reflected
onto the screen/wall. There are 3 times of overhead projectors; transmissive, reflective, and opaque.[1]





Parts of an Overhead Projector


An overhead projector is a large box, and on the large box there are several parts. Some of the parts include a bright lamp, fresnel lens, a cooling fan, a mirror, and a long arm.

Capture1.JPG
This image to the left is a detailed diagram of the major parts of an overhead projector. To the right, are all of the numbered parts that correspond with the diagram of the overhead projector (left).
Lamp and Reflector - The lamp is the light source, and it is found on the
base (box) of the overhead projector. The reflector is placed being the lamp,
so that it can direct the light forward toward a mirror. The reflector is key
because it prevents light from being spread inside the base. If there wasn't
a reflector, the image being projected would be very dim. The condenser is
used to focus or condense the light onto the mirror, it is positioned between
the lamp and the mirror in the base.[2]

Blower - It is important to have a cooling fan because the base unit produces
a large amount of heat, and the overhead projector requires a fan to prevent it
from blowing out. An electric motor powers the blower, and attached to the
motor is the fan that releases cool air within the base of the unit.[3]

Base Mirror - A mirror can be found in the base unit, which is at an approximate
angle of 45 degrees. This mirror is there to change the angle of the light produced
by the lamp and reflector from its original horizontal direction. Then light is reflected
and directed upward by this mirror through the projector's stage.[4]



Capture2.JPG
On the left is a cooling fan, which is place inside the base of the overhead projector. The cooling fan is used to prevent the overhead projector from reaching high temperatures.. On the right is an example of a projection lamp. The projection lamp is the light source for the overhead projector.
Projection Stage -This is a glass surface where transparencies are placed to be
projected. The projection stage is also where the Fresnel lens are placed to focus
and magnify the image upward. The Fresnel lens have a unique/fuzzy appearance to
it because the surface of the Fresnel lens is made of concentric rings.[5]

Upper Section - Above the stage, there are more parts that consist of a focusing knob, an objective
lens that admits light sent through the Fresnel lens and another mirror to guide the image ahead onto
the wall/screen. the focus knob is used to focus image or written material by moving the upper section
up or down.[6]







How to Produce a Magnified Image

Overhead projectors are like telescopes, they both use the work of mirrors. However, overhead projectors uses mirrors to project images or write
overhead.jpg
This image shows a simple understanding of how an overhead projector works.

material onto a screen. The way a overhead projector works is very simple. First, the lamp, which is the light source, produces light towards the first
mirror (found inside the base unit). The first mirror is tilted at a 45 degree angle so that it can reflect the light upwards. The light then travels through
the Fresnel lens, where the transparency is placed. Then, the light goes through the objective lens, and gets absorbed by the second mirror. Finally,
the light and image/written material reflects onto the wall/screen from the second mirror.[7] An overhead projector projects the image from the transparency
onto a flat mirror to make upright because all images formed by mirrors or lenses are inverted.[8]

overhead_(1).jpg
A view of the Fresnel lens on a overhead projector.




Focusing the Image

The focusing knob is what is used to focus the image or written material that is being reflected by the overhead projector. The focusing knob is usually black, and it is
focusing_knobs_PA083542.JPG
This is an example of a focusing knob.

found on the arm of a overhead projector. By turning the focus knob, the second mirror will adjust its height depending on the direction that the knob is being turned to.
The image will then became bigger or smaller depending on the distance between the overhead projector and the screen. More advanced and better quality overhead
projectors have an option of a adjustment wheel/screw. With this option, the lamp can be moved closer and away from the Fresnel lens. The projected image is evenly
white when at its best focal length. If the second mirror becomes too high or too low, then this will result in blue or brown colour fringing around the projected image. By
turning this knob, it will bring back all of white in the projected image.[9]









Comparing a Overhead Projector and a Microscope

f0522-01.jpg
A ray diagram of a light microscope.


14064_234_1.jpg
A ray diagram of an overhead projector.








An overhead projector and a light microscope are very similar. They both have a light source and both use the work of mirrors and lenses. One noticeable difference is that the last lens that light goes through in the light microscope is converging rather than diverging, which is found in overhead projectors. The use of converging lens in a light microscope is necessary because that is how the image will fit the eye of the observer. In overhead projectors, diverging lens are key because they enlarge the image onto the wall/screen.[10]













Latest Technology

Overhead projectors are over a century old, and over the years newer and much more advanced technology has come along and have erased the need of overhead projectors.
PS3-Projectors.jpg
An image of a much more advanced projector.

As seen in the image to the left, projectors are much smaller and quieter these days. Projectors such as the one on the left, do not contain any mirrors and can be operated
by a computer. However, these projectors still use lenses. These projectors can project much more than still images, they can now project movies (video) and in colour rather
than black and white. Projectors now have an option to hook up a computer/TV/gaming console.

Here is a video showing the change in technology in schools, going from overhead projectors to Smart Boards!




















[11]





Glossary

Transparencies - c
apable of transmitting light so that objects or images can be seen as if there were no intervening material.Reflector - a surface or object that reflects light, sound, heat, etc.Condenser - a lens that concentrates light into a small area.Inverted - upside down.Converging - to tend toward or approach an intersecting point.Diverging - to go or extend in different directions from a common point; branch out.


  1. ^ What is an Overhead Projector?. (n.d.). wiseGEEK: clear answers for common questions. Retrieved May 27, 2012, from http://www.wisegeek.com/what-is-an-overhead-projector.htm
  2. ^ Miller, D. (n.d.). Major Parts of an Overhead Projector | eHow.com.eHow | How to Videos, Articles & More - Discover the expert in you. | eHow.com. Retrieved May 27, 2012, from http://www.ehow.com/about_5314657_major-parts-overhead-projector.html
  3. ^ Miller, D. (n.d.). Major Parts of an Overhead Projector | eHow.com.eHow | How to Videos, Articles & More - Discover the expert in you. | eHow.com. Retrieved May 27, 2012, from http://www.ehow.com/about_5314657_major-parts-overhead-projector.html
  4. ^ Miller, D. (n.d.). Major Parts of an Overhead Projector | eHow.com.eHow | How to Videos, Articles & More - Discover the expert in you. | eHow.com. Retrieved May 27, 2012, from http://www.ehow.com/about_5314657_major-parts-overhead-projector.html
  5. ^





    Miller, D. (n.d.). Major Parts of an Overhead Projector | eHow.com.eHow | How to Videos, Articles & More - Discover the expert in you. | eHow.com. Retrieved May 27, 2012, from http://www.ehow.com/about_5314657_major-parts-overhead-projector.html
  6. ^





    Miller, D. (n.d.). Major Parts of an Overhead Projector | eHow.com.eHow | How to Videos, Articles & More - Discover the expert in you. | eHow.com. Retrieved May 27, 2012, from http://www.ehow.com/about_5314657_major-parts-overhead-projector.html
  7. ^





    How Overhead Projectors Work. (n.d.). The Tech-FAQ. Retrieved May 27, 2012, from http://www.tech-faq.com/how-overhead-projectors-work.html
  8. ^





    Describing Images. (n.d.). Describing Images Made From Mirrors and Lenses. Retrieved May 27, 2012, from http://www.leydenscience.org/physics/electmag/image_des.htm
  9. ^





    Overhead projector - Wikipedia, the free encyclopedia. (n.d.). Wikipedia, the free encyclopedia. Retrieved May 27, 2012, from http://en.wikipedia.org/wiki/Overhead_projector
  10. ^





    Portable Overhead Projector. (n.d.).Religion, Chaplain Reference and Training Manuals. Retrieved May 27, 2012, from http://religionmanuals.tpub.com/14229/css/14229_334.htm
  11. ^




    Overhead Projectors to Smart Boards - YouTube . (n.d.). YouTube - Broadcast Yourself. . Retrieved May 27, 2012, from http://www.youtube.com/watch?feature=player_embedded&v=t89-6UG4-jw