Which type of spherical aberration is characterized by a 'teacup and saucer' image due to the asymmetric tangential and sagittal foci?

Which type of spherical aberration is characterized by a 'teacup and saucer' image due to the asymmetric tangential and sagittal foci?

• A. Longitudinal
• B. Radial
• C. Coma
• D. Curvature of field

Answer: (B)

Spherical aberration describes how rays that hit a lens at different distances from the optical axis don’t all focus at the same plane. When the aberration varies with radius in the pupil, you get what’s called radial spherical aberration. This radial dependence means rays from different parts of the pupil don’t converge together, producing two distinct focal planes that show up as asymmetric blur patterns when you consider tangential and sagittal directions. The resulting image pattern can be described, in a classic way, as a teacup and saucer—one focal form corresponding to one plane and a second, offset form corresponding to the other plane. This is different from longitudinal spherical aberration, which mainly changes where on the optical axis the rays focus but doesn’t inherently produce the tangential/sagittal asymmetry. Coma, on the other hand, creates comet-like off-axis blur with a directional tail, and curvature of field causes the image plane to be curved rather than flat across the field.

Spherical aberration describes how rays that hit a lens at different distances from the optical axis don’t all focus at the same plane. When the aberration varies with radius in the pupil, you get what’s called radial spherical aberration. This radial dependence means rays from different parts of the pupil don’t converge together, producing two distinct focal planes that show up as asymmetric blur patterns when you consider tangential and sagittal directions. The resulting image pattern can be described, in a classic way, as a teacup and saucer—one focal form corresponding to one plane and a second, offset form corresponding to the other plane.

This is different from longitudinal spherical aberration, which mainly changes where on the optical axis the rays focus but doesn’t inherently produce the tangential/sagittal asymmetry. Coma, on the other hand, creates comet-like off-axis blur with a directional tail, and curvature of field causes the image plane to be curved rather than flat across the field.