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.
Read more about Focal Cloud: Satellite Dish Effects
Famous quotes containing the word cloud:
“It cannot be denied that for a society which has to create scarcity to save its members from starvation, to whom abundance spells disaster, and to whom unlimited energy means unlimited power for war and destruction, there is an ominous cloud in the distance though at present it be no bigger than a man’s hand.”
—Arthur Stanley Eddington (1882–1944)