Which of the following is true regarding a teacup and saucer image?

• A. Radial Spherical Aberration
• B. Longitudinal Spherical Aberration
• C. Coma
• D. Curvature of Field

Answer: (A)

Radial spherical aberration is at play when light from different zones of a spherical lens comes to focus at different points along the optical axis. That means peripheral rays don’t converge with the paraxial (central) rays. In a teacup-on-a-saucer image, the central portion can appear sharp (from the paraxial rays) while the outer parts form a larger, blurred halo or “saucer” around it due to the outer rays focusing at a different axial position. This creates a small, crisp teacup with a surrounding blurred ring, which is the telltale sign of radial spherical aberration. Curvature of field would make sharpness vary across the image plane, coma would smear off-axis points into tails, and longitudinal spherical aberration shifts the focus along the axis with pupil change rather than producing this concentric sharp/blur pattern.