Simulated Optical Bench
Left-Click on background to make a new lens
Left-Click on a lens to delete it
Left-Drag a lens left/right to move it
Left-Drag a lens up/down to resize it
Right-Click on a lens to toggle concave/convex
Right-Drag a lens to change focal length
On some computers, Right-Click and Right-Drag might not work.
If that happens, then use the left mouse button while holding down the ALT key.