Instructions:

1. Click on a lens to test that lens.

2. Slide the lens to the right or left to see how changing the position of the lens changes the image of the top.

3. You can also slide the top to the right or left to see how changing the position of the top changes the image of the top.

4. Click on the Ray Trace button to see how  the lens bends the light coming from the object to form the image you see. When you are done looking at the ray trace, click on the Show Image button.

5. To test a new lens, click on that lens.