Introduction About AO Vision Ray Tracing Shack-Hartmann Contact Us
Light
Light can be described as a traveling wave - like the waves you might see on a beach. When people think of light, they usually think of light we can see; this light makes up the visible spectrum. There are many sources of visible light- light bulbs, headlights, fire- but most of the objects we see are not sources of visible light. Typically, we see light bouncing off of an object and back to our eyes. Each of our eyes has a lens, that enables us to focus objects on our retina so that we can see clearly.
Lenses
Some familiar forms of lenses are contact lenses, glasses, and cameras. These lenses (curved pieces of glass or clear plastic) are useful because they take incoming light and focus it to form images. Telescopes, microscopes, and magnifying glasses all use lenses to change the way that we see things.
The F-Box Demonstration
The F-box demonstration allows a user to investigate the properties of lenses in a hands-on way. Using the F-box, a person is able to see how three different lenses affect the same incoming light and compare the effects side by side.
| A light source, in the shape of the letter "F", illuminates a frame holding three convex lenses with different focal lengths. Convex lenses are thicker at in the center than the edges, and the distance at which they focus light depends on how curved the lens is. |
Figure 1: Convex Lenses. Lenses that are more curved focus light at a closer distance. |
| Each lens creates an image of the F that is projected on a card placed behind the lens. A person can move the cards closer to or farther from each lens to find the point where the image is focused, in the process observing how lenses of different thickness change the distance at which the image focuses. |
Figure 2: The F-box in action. |
The demonstration also shows the relative sizes of the images created by the different lenses and how that varies with focal length and distance from the light source. Then, by placing a shield over the lenses to make the openings smaller, one can see that the size of the lens does not affect the size of the image; this merely affects the brightness. This is something that comes as a surprise to many people who assume that bigger telescopes are better because they magnify the images more.
The F-box can be used to demonstrate many properties of lenses. It has been very effective in helping students understand lenses in a more concrete way than can be done through 2-dimensional ray tracing or the current models of classroom demonstrations.