blue lines	trace of light path
green lines	backward tracing for virtual image
small red lines	distances f and 2*f away from the center of lens.
1st textfield	current mouse position (x , y) relative to lens
white vertical line	reference line (you can click and drag it left/right)
yellow line	light path for paraxial ray assumption(mirror only)

Parameters can be changed :

1. Select Lens for thin lens effect(default)
2. select mirror for concave/convex mirror effect
default: assume paraxial ray (you can turn it off)
3. press toggle button +/- to change between converging/diverging lens
4. Move the object
click near tip of the object, and drag it to where you like it and release the mouse button.
5. Move the lens/mirror:
click near center of the lens, and drag it to left or right.
if click with left mouse button, only lens will move.
if click with right mouse button, object will move with lens.
6. Change the focus length of the lens/mirror
click near the top/bottom of the lens/mirrir, then drag the mouse . Try it!
7. if you adjust the size of window, parameters reset to default values.
8. you can open more then one window to compare different cases, close the created window to Quit. Press to open another Lens window!
9. you can change the following parameters inside the "textfield".

Would you like to try a thick lense or a thin lens combination? related java applet lens