Focal Cloud

A focal cloud is the collection of focal points of any imperfect lens, whether optical, electrostatic or electromagnetic. This includes Parabolic antennas and lens-type reflective antennas of all kinds. The effect is analogous to the circle of confusion in photography.

In this focal cloud illustration, a perfect reflector would focus all beams into the blue spot. Due to imperfections of lens construction, the actual signal beams follow the red path to several different focal points, which form the focal cloud. Lens-reflector artifacts, geometry and other imperfections determine the actual radius of the focal cloud.