This eight-minute video explains the principles of convex lenses by blending video, animation, and still images. It segments the convex lens into pieces, much like one sees in an optical bench -- triangular prisms at top and bottom, trapezoidal prisms adjacent, and a rectangular prism in the precise middle. Animated ray diagrams show clearly how light refracts at both edges of the convex lens, and bend toward the principal axis. The animation depicts 3 fundamental actions of convex lenses:  1) A ray traveling parallel to the principal axis passes through the principal focus, 2) A ray traveling through the focus will emerge parallel to the principal axis, and 3) A ray traveling through the optical center will emerge undeviated.

Please note that this resource requires Flash.