Brief description and instructions (DRAFT):
This applet illustrate the basics of focusing with both a lens and with a pupil.
The applet is organized as follows, in each case, the controls for the item are below the item on the screen:
For the lights, you can turn them on and move them. There are sliders to move each light separately or both together. You can control the width of the pupil and the thickness of the lens when they are on the screen. You can also change the position of the white sheet of paper.
Since the light sources are dots, they are in focus when they are also dots on the white sheet of paper. Notice how the lens and the pupil are differently able to focus objects at different distances.
Click here to open the applet. It will open a new window that will fill your screen.