Introduction About AO Lens Vision Shack-Hartmann Contact Us
Waves of traveling light are also called rays. To help people understand how light rays actually form images, we have designed a demonstration that enables viewers to see how light rays converge and diverge in optical systems. One major application of this is with telescopes. Many people are somewhat familiar with telescopes and have see the textbook pictures of the light paths in a telescope, but the concept can be difficult to understand- especially when the optical system involves many lenses and/or mirrors. This demonstration is so useful because it allows an observer to walk around the image and look at it from all sides, something difficult to do with a two-dimensional picture.
We originally designed the ray tracing demonstration to show the path of light through a telescope, but quickly realized that any optical system could be ray traced using the same principles. We have designed both a refracting and reflecting telescope model, and currently we are designing a model of the eye.
Ray Tracing Through Telescopes
Telescopes can be divided into two main classes - refracting telescopes and reflecting telescopes. Reflecting telescopes can also be divided into two different classes depending on where the secondary mirror is placed Telescopes are very useful for ray tracing exercises because they use both mirrors and lenses to gather light and image objects.
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Refracting Telescopes The first telescopes used lenses to gather and focus light from the sky. Light from a star enters the telescope though the objective lens, a convex lens. This lens focuses the light to a point. Another lens is placed near the focal point of the first lens, and the emerging light is parallel. A telescope that uses lenses like this is called a refracting telescope. |
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Reflecting Telescopes Reflecting telescopes use mirrors instead of lenses to gather and focus light. Light first hits a primary mirror, where it is reflected to a focal point. In front of the focal point another mirror is placed, which reflects the light at a 90degree angle. Just after the light reaches its focal point, an eyepiece (lens) is placed that causes the beams to emerge parallel. |
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The Demonstrations
In the ray tracing demonstrations, the incoming light is produced by an array of six lenses. These lenses shine into a tank filled with a solution of soap and water. The solutions scatters the laser beams, allowing an observer to see them clearly. As the light rays travel through the telescopes, you can clearly see them coming to a focus and then emerging parallel from the eyepiece lens. Because this is a three dimensional representation, you can walk around the tank and look at how the light bends and focuses from the front, back, both sides, and above. You can also replace the original lens and mirrors with ones of different focal lengths or different sizes and observe the effects. These pictures are from the reflecting telescope demonstration.
This is a picture of the optical set-up for the reflecting telescope demonstration. The mirrors and lenses are suspended in the water by rods with crossbeams resting on the top of the tank, allowing users to easily adjust the distances between the optics and see the results. The laser array is mounted on a height-adjustable stand located outside of the tank. You can see the laser array on the right side of this picture, pointing into the tank.
Ray T racing Through the Eye
Our eyes are convex lenses, but they are not perfect. Many people have to wear contacts or glasses to correct for the shape of their lenses, stigmatisms, etc. In order to model the eye, we are going to use a large, spherical container filled with the same solution as we used in the telescope demonstrations. At one end, a convex lens will represent the cornea. Using a similar array of lasers we can show how the eye focuses light. By using a system where we can interchange lenses representing "perfect" corneas with misshapen ones, we can easily show how adding another lens (i.e. contact lenses or glasses) corrects many vision problems.
Ray Tracing Other Optical Systems
Another interesting application that we are working on is building a tool for interrogating any optical system. For example, a teacher could set up a system of lenses or mirrors and have the students draw the paths of the rays and determine their final position, size, etc. Then, the teacher could send the lasers through the system and the students could take a portable, clear box filled with the solution and test their predictions.
The path of light rays though any optical system can be seen using this type of design. No matter what the set up, the basic engineering for any three-dimensional ray tracing system is captured in these demonstrations.