The Lensmaker's equation describes the relationship between lens material (index [i]n[/i]), radii of curvature of spherical lens surfaces, and locations of object (light source) and image.[br][br]This applet allows you to explore the conditions under which the Lensmaker's equation is true -- or nearly true -- and the conditions that violate the Lensmaker's equation.

To send parallel rays through the lens, use the Input bar to put the source at a large negative x distance: For example,[br]Source=(-1E10,0)