Which statement best describes the difference between a spherical lens and a cylindrical lens?

• A. A spherical lens deviates rays of light in more than one direction.
• B. A spherical lens deviates rays of light in the same direction; a cylindrical lens deviates rays in more than one direction.
• C. A spherical lens bends light at a constant speed.
• D. A cylindrical lens bends light equally in all directions.

Answer: (B)

Understanding how lens shape affects bending of light helps explain why spherical and cylindrical lenses behave differently. A spherical lens has identical curvature in all directions around its axis, so light entering parallel to the axis is bent by the same amount no matter which plane you view it from. This creates a uniform deviation in a single, consistent direction, leading to a single effective focal point for paraxial rays.

A cylindrical lens, by contrast, has curvature in only one meridian and is flat in the perpendicular meridian. That means light is bent more strongly along the powered meridian than along the perpendicular one, so rays are redirected differently depending on their orientation. This results in focusing behavior that varies by direction, effectively deviating light in more than one direction and producing astigmatic focusing.

So the difference is that a spherical lens bends light uniformly in all directions, while a cylindrical lens bends light differently along different directions.