human
What is the difference between a spherical, cylindrical and an ellipsoid lens?
assistant
Spherical lenses are shaped like a sphere. Cylindrical lenses are shaped like a cylinder. Ellipsoid lenses are shaped like an ellipse. The main difference between them is that spherical lenses focus light in one plane only, while cylindrical lenses focus light in two planes, and ellipsoid lenses focus light in three planes.