Make a Projector

Introduction: (Initial Observation)

Projectors are devices that throw light or images on a distant surfaces for the view of an audience. Depending on the design and purpose, projectors are classified in many different types. Light projectors used in theatrical lighting are often known as Ellipsoidal spotlights. Other types of projectors include slide projector, overhead projector, movie projector, transparency projector, digital projector, and many more.

A powerful light projector can produce a strong beams of light that can travel many miles.

Artists use projectors to create super large paintings. In this project you will design and construct a slide projector. You may also perform additional experiments with your projector in order to see how does the type of lens affect the distance or size of the projected image.

Please note that parts of this project guide are for higher grades and more advanced students. Please ignore the contents that exceed your project plan.

Information Gathering:

Gather information about lenses and how they can be used. Learn about the history of using lenses in making light projectors, slide projectors and movie projectors. Read books, search the Internet or ask professionals who might know in order to learn how you can make a simple slide projector. Keep track of where you got your information from.

Following are samples of information that you may find.

Before invention of light bulb by Thomas Edison, simple projectors were made using the light from a kerosene burning lantern. In these projectors, the burning flame in lantern provides the light for projection. This type of projectors were known as magic lantern.

In 1880’s the ‘Magic Lantern‘ was used to show black and white photographs which had been printed on square glass plates. These shows were the closest thing at the time to going to the cinema !

Search the Internet for magic lanterns to see more.

See more samples of magic lanterns: 1, 2, 3, 4, 5 (Click on numbers)

Lens Projection

All slide and motion picture projectors work in basically the same way. In modern projectors, an optically refined lens is used to form an image of a “slide” placed in the strongly illuminated aperture. The source of illumination is a high-powered lamp.

Its light is gathered and passed through the aperture in such a way that it converges on the entrance element of the projection lens. The slide can be anything from the conventional glass plate with a photographic image bonded to it to a manually painted glass.

The size of the projected image depends on the slide size, the focal length of the projection lens and the distance to the projection surface.

Efficiency depends on the light source, the light gathering system, the density and size of the slide. Sharpness of the image depends mainly on the optical quality of the lens.

Theatrical lens projectors have evolved from custom-made units often made in-house by an optical specialist, to modern commercially manufactured units, some of which are masterpieces of the optical engineer’s work but very expensive and bulky.

Modern luminaries such as ellipsoidal reflector spotlights and automated luminaires are basically projectors. Ellipsoidal reflector spot-lights can be fitted with gobos to produce simple images which can cover about the same area as the pool of light normally produced by the luminary. Similarly, automated luminaries can be fitted with slides and will produce high quality images covering about the same area as the luminary would otherwise illuminate. With the exception of situations where exceedingly powerful projections are needed, automated luminaries are rapidly monopolizing the field of scenic projection wherever they are affordable.

The Optical System

All parts of a good projection system are centered on its optical axis. This is a line through the center of each optical element and, ideally, extending to the center of the screen. Not only should all parts be centered on the optical axis, their optical planes should also be at right angles to it. Under these conditions, there will be no distortion due to misalignment, but optical distortion from lens or reflector faults may still exist.

The lamp house

The lamp house is the enclosure around the light gathering apparatus that contains spill light from the lamp and supports the lamp and its electrical leads. It may also carry the aperture apparatus and the objective lens.

A lamp house is much like the housing of a high-powered spotlight; it must withstand heat, contain dangerous radiation, withstand occasional rough handling, and may have to be engineered to contain the violent explosion of a high-pressure lamp. In the case of theatrical projectors, it often fitted with mounting equipment such as a yoke and “C” clamp or a base that allows accurate tilting and panning.

Collecting the light

The principle of collecting light in a projector is the same as collecting light in a spotlights. However collecting light for projection is more demanding. The object of the system is to gather as much of the light output of the lamp as possible and direct it through the slide and into the rear element of the objective lens.

In general, two approaches are to be found:

1. A conventional spherical mirror, plano-convex lens arrangement upgraded by the use of the best quality mirror and one or more high-quality lenses designed to converge the cone of light to a diameter equal to the diagonal of the slide. Furthermore an additional lens, sometimes called a “collector,” may be installed just in front of the slide to converge the light passing through the slide into the rear element of the objective lens.

2. Adaptations of the ellipsoidal reflector system may be more efficient overall than the lens system above. These gather and direct the light with greater efficiency than the lens train method. These special mirrors can also be made of dichroic material (see Handling Heat below).

Handling heat

Any incandescent source powerful enough to be useful in scenic projection will produce a large amount of heat, part of it as heated air and the rest as infrared (IR) light. The heated air must be exhausted either by convection or forced ventilation. The infrared is picked up by the collection system and passed along to the slide unless special precautions are taken.

A “low tech” solution to this problem is to install a heat filter of IR blocking glass in the optical chain just before the slide. This filter will absorb the IR, converting it to heat which must be removed by air circulation.

A better solution is to install a cold mirror (dichroic filter) at the above position. This will pass the visible light and reflect the IR back toward the source. In addition, using a hot mirror (also a dichroic filter) as the light collecting mirror (spherical, ellipsoidal or special geometry) will pass the IR through the back of the lamp house and reflect the visible light toward the lens. If these measures are not sufficient, or if they prove too costly, the slide may have to be cooled by a blast of air from a special fan. This will make additional noise and require extra electrical circuitry.

Image Material

Slide shows both on- and off-stage date well back into the nineteenth century. These used painted slides first and later photographs.

Moving stage effects such as rain, clouds and fire produced by rotating disks moving through the aperture have an equally long history. Modern moving effects include a wide variety of moving gobos and strips of film accurately controlled and highly sophisticated in their quality of images. Furthermore, projection specialists even today may devise apparatus as needed for specific shows. In any case, this image material must be accurately placed on the optical axis, care-fully located within the depth-of-focus region of the lens and fully illuminated.

Whatever the image material, it must be capable of resisting the effects of the heat in the beam and, if it is a photographic or painted slide, resisting the fading action of the light. With the exception of silhouette-type slides intended to produce shadow images, the lower the density of the image the better. A photographic color slide developed for the lightest density possible while still retaining the image quality needed, can often add more to the brightness of the image than any other single element in the entire optical system.

Objective Lens

The objective lens is the most important part of the optical system. Ideally it should transmit a high percentage of the light striking its rear element, focus every part of a large slide sharply and evenly and distribute the image over the screen without hot spots or dark areas. It should do all of this at very short throw distances and be highly resistant to the effects of high heat from the light beam. Finally, it should be light in weight, small in size, and economical to purchase. Such a lens does not exist.

The objective lens, or better, a set of objective lenses, will usually be one of the most expensive parts of the theatre’s projection system. The best lenses are specially made for this service and come as close to the ideal as cost and optical skill will allow. One major difficulty is the optical fact that the shorter the focal length of the lens, the more difficult it is to make it meet the other theatrical requirements. Thus the lenses most needed—those for short throws—are the very lenses that are hardest to make and are therefore the most costly.

Objective lenses are described by their focal length stated in inches or millimeters and their speed (the efficiency with which they handle light) stated as an “ƒ” number (e.g., 4.5 inches, ƒ=3.0). Objective lenses may come as part of a system or be purchased separately. Since the out-side diameter of objective lenses varies considerably from lens to lens, the projector must be equipped to allow the secure but adjustable mounting of each lens. Worse, projectors designed for a particular set of lenses are not likely to accept lenses of another make without devising special adapters.

Note that camera lenses will not serve as projection lenses for high-powered projectors even though they may have the proper speed and focal length. They cannot handle the heat load and will be destroyed.

How to measure the focal length of the lens?

Focal length of a lens is very important in designing a projector. The reason is simple. No image will be formed if the slide, light source or the screen are in the focal distance of the lens. In other words, the distance from the light source or slide to the lens must be more than the focal distance of the lens. That is why you need a lens with small focal length.

To measure the focal length hold the lens under the sunlight so that the sun rays hit the lens in a right angle. Then move the lens up and down until it forms one bright spot of the sun. While the spot is the smallest possible, the distance between the lens and the spot is the focal length. Measure the distance using a ruler stick.

The reason that this method works is that in a converging lens, the image of far objects will form on the focal point. If you are doing this a night, the image of any distant light source or the image of the moon will work as well.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

Problem statement: It is time consuming, hard, and often impossible for a large group of people (in classroom or conference room) to view a small image at the same time. People who do not see an image, may not be able to understand and participate in a discussion about that image. It is an essential need to make a device that can enlarge an image and project it on a screen so many people can see that at the same time.

Purpose:

The purpose of this project is to construct an slide projector.

You may also want to study on a specific question such as:

How does the distance of the slide to the lens affect the distance to the image to the lens? What can you do to get a larger image?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variable (also known as manipulated variable) is the distance of the slide to the lens.

Dependent variable (also known as responding variable) is the distance of the image to the lens.

Constants are the lens, light source, slide and other projector components.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. This is a sample hypothesis:

The image will be dimmer and larger if the screen is further away from the lens. My hypothesis is based on my observation of flashlights that lit a larger area when they are further away from a surface.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Make a light projector

Introduction:

Light projectors allow you to extend the light radiation to far distances where normal light can not reach. Light projectors can change the direction of light beams and form a stream of parallel beams. You can use a light projector to see the bottom of a dark well or the end of a dark cave. Some flashlights have reflective mirrors and lenses that can almost work like a light projector.

Material:

1. One 6-volt screw base miniature light bulb and base
2. One 6-volt battery (lantern battery)
3. Wire leads with alligator clips or any pair of insulated wire such as thermostat wire or bell wire.
4. A converging lens (Double Convex) with small focal point (2 to 6 inches or 5 to 15 centimeters)
5. Cardboard, paper tubes, tapes, scissor, and ruler.
6. A dark or low light room.

Procedure:

1. Measure and record the focal point of your lens (call it F). How? See the gathering information section.
2. Find or make a paper tube with the same diameter as your lens and about 2F long. (So the length of paper tube is twice the focal point of your lens).

3. Use tape, a few small screws or any other method to secure the lens on one end of the tube.

4. Find or make another tube that is smaller than the first one and can enter the first tube.

5. Close one end of the smaller tube using a round cardboard and make a small hole in the middle of that so the light bulb screw can pass through.

6. Connect the wires to the base and then screw the bulb on the base so that they will reside in two opposite side of the round cardboard.

7. Connect the two wires to the battery so the light bulb will turn on. Insert the light tube into the lens tube while looking at the projection. When do you get the smallest and brightest projection? Is it when the light bulb is at the focal point of the lens?

Make a slide projectors

Introduction:

Slide projectors are very similar to the light projectors. The only difference is that you place a slide between the light bulb and the lens.

Procedure 1:

You can simply modify your light projector and make a slide projector. To do that, place a cylindrical cap over the light bulb, cut a rectangular hole on the flat bottom of the cap and mount a slide (or a film). Move the inner tube so that the distance between the slide and the lens will be slightly more than the focal length of the lens. See the projected image on a wall that is a few feet away from the lens. Focus the image by moving the inner tube back and forth.

Procedure 2:

1. Get a 20″ x 3″ wooden block as the base for your projector.
2. Get a 3″ x 3″ wooden block as the base for the lens. Glue cardboards or Popsicle sticks on two opposite sides of the lens base so it can slide safely over the projector base.
3. Make a hole in the middle of the lens base; unscrew the plastic handle of the lens and screw the lens on the lens board.

4. Temporarily mount the lens board with lens on the middle of the projector board.

5. Get another 3″ x 3″ wooden block as the base for the light bulb. Glue cardboards or Popsicle sticks on two opposite sides of the light base so it can slide safely over the projector base.

6. Mount a light bulb receptacle and light bulb over the light base such that the light bulb filament (the part that produces light) is at the same level with the center of the lens.

7. Use cardboard to construct a cube over the light base. On one side of the cube that is faced to the lens cut a rectangle, the size of the slide image. Cut the rectangle where the center of rectangle is at the same level as the center of the lens.

8. Tape your slide over this window.

9. Connect the wires to the light bulb and battery so the bulb will turn on.

10. In a dark room hold the projector faced to a white wall about 6 feet away. Slide the lens to that end of the projector base that is close to the wall. Now slowly move the light base (with its cubic cover) and slide towards the lens. Before the slide gets to the focal point of the lens you should see a clear image on the wall.

11. Describe the image.

Actual pictures of a sample projector

Lens and the light base:

As you see, an additional piece of wood is used to rise the light bulb. In this way the center of the light bulb and the center of the lens will be at the same height.

The light box is constructed with cardboard. Another piece of construction paper is formed to hold the slides. Box is completed by connecting the sides using clear tape.

Completed box is open from the bottom, so it can be placed like a cap over the light base.

When you place the cap, the window will be right in front of the light bulb.

The wires are connected and the light is tested before placing the cap. Since the light bulb is clear, it is nice to cover the light with any opaque material. In this way the light will come out without any glare. Alternatively you may place a wax paper between the bulb and the slide.

For best results, cover inside the box with aluminum foil or white paint.

This is the completed model. Both the lens and the light box can slide back and forth on the wooden base.

Please email your digital pictures to pictures@ScienceProject.com

Experiment 1: How does the distance of the slide to the lens affect the distance to the image to the lens? What can you do to get a larger image?

Introduction:

Now that your slide projector is ready, you can use it to find out the relation between the image distance and the slide distance to the lens.

Procedure:

1. In a dark room, place your projector about 2 feet away from a white wall. (the distance from the lens to the wall must be two feet)
2. Move the slide box back and forth until you focus the image on the wall.
3. While the image is focused, measure and record the distance from the slide to the lens.
4. Move the projector back exactly one foot. (At this time, the distance from the lens to the wall must be three feet).
5. Move the slide box back and forth until you focus the image on the wall.
6. While the image is focused, measure and record the distance from the slide to the lens.
7. Repeat this cycle for distances of 4 and 5 feet from the wall. Record your results in a table like this:
   

   Image distance (lens to screen distance)	Slide to lens distance
   2 feet
   3 feet
   4 feet
   5 feet
   6 feet

   Draw a graph:

   Use your results table above to draw a line graph. Use the X axis (horizontal) for Image distance. Use the Y axis (vertical) for slide distance. Mark the points and the connect them together to make a line.

Materials and Equipment:

This is a sample list of material.

Material:

1. One 6-volt screw base miniature light bulb (MiniScience part#E0502_1).
2. Miniature base for the light bulb (MiniScience part#MINIBASE )
3. One 6-volt battery (lantern battery)
4. One slide or film
5. Wire leads with alligator clips or any pair of insulated wire such as thermostat wire or bell wire.
6. A converging lens (Double Convex) with small focal point (2 to 6 inches or 5 to 15 centimeters) (MiniScience part# GMAGVG)
7. Cardboard, paper tubes, tapes, scissor, and ruler.
8. A dark or low light room.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

If you do any calculation for your project, write your calculation in this section of your report. The distances measured in the above experiment, may also be calculated.
The theory predicts that 1/o + 1/i = 1/f.

In this formula

o is the object distance (slide distance).

i is the image distance (screen distance)

f is the focal point of the lens

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

How does the focal point of a lens affect the design and image magnification in a slide projector? Which lens is best for a projector? High focal point or low focal point?

How does the curvature of a lens affect the design of a projector? Can you use a bi-concave lens in a projector?

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

Visit your local library and find books related to optics, lenses, cameras and projectors. List such books as your references or bibliography.

Following are some related web references:

• Light and Optics
• Image formation by lenses
• Picture of an old slide projector
• Picture of another old slide projector
• Historical slide projector
• Baker Microslide projector
• LCD projector design
• Another historic projector
• Overhead projector
• Imaging properties of a simple lens
• Pictures from light (A nice observation)

Questions and Answers

Q. What is the scientific principle of projector?

A. Scientific principle of projectors, cameras, telescopes and microscopes is the refraction of light when it passes from one media to the other.

Lenses that are usually made of glass or clear plastic can refract and converge light beams and form an image of the light source.

Q. What is the theory in regards to the light going through the lens/magnifying glass.

A. When light from an object or a light source gets to a convex lens, it forms an upside down image of the object (or light source) in the opposite side. The location of the image (or the distance of the image to the lens) vary based on the distance of the light source to the lens.

• If the light source is very far, the image will form on the focal point of the lens. (That is how I locate the focal point and measure the focal distance of lenses).
• As the light source gets closer, the image moves further away from the lens.
• When the object gets to the focal point of the lens, the image will form at a very far distance in the opposite side.

Q. I am not getting a clear image with my slide projector. What should we do?

A. Different conditions contribute in getting a clearer image.

1. The light source must be smaller and stronger.
2. The light source must be further away from the slide.
3. The room must be darker so that the dimmer image will also be visible.