Principal Ray Diagram Simulation
Here you can see what is called a principal ray diagram. We have constructed the image of the candle from the three principal rays, as we explained before. This interactive animation allows you now to move the object relative to the lens, and to observe what happens to the image. Click on the object, the candle on the left, and drag it to different positions. The three principal rays are always constructed the same way: one goes straight through the middle of the lens, one goes parallel to the optical axis, and then through the focal point, and one goes through the focal point between the object and the lens, and leaves the lens parallel to the optical axis. Take some time moving the object back and forth, and try to answer the following questions: What happens to the position of the image when you move the object closer to the lens? What happens to the size of the image when you move the object closer to the lens? You will notice that the animation does not allow you to move the object closer than about two focal lengths to the lens. That's because we are trying to simulate the situation for our eye: Everything we look at is a lot further away from our eye than the size of our eyeball, which is about one inch in diameter. We'll come back to this in a moment. For now, make sure that you also observe what happens when you move the object further and further away from the lens. Where does the image move? Remember what we concluded from our experiment in the video about the position of the image of a very far away object? Is this consistent with the result of this simulation?