Which type of spherical aberration is caused by oblique astigmatism and is due to rays hitting the lens or interface obliquely?

Which type of spherical aberration is caused by oblique astigmatism and is due to rays hitting the lens or interface obliquely?

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

Answer: (B)

Radial spherical aberration is the one that arises when oblique incidence into a spherical surface causes rays at different radii to focus differently. When light enters at an angle, the astigmatic effect of oblique rays means paraxial and off-axis rays don’t converge in the same way, and this leads to focusing errors that depend on how far a ray is from the optical axis. In other words, the blur varies with radius because the rays hit the lens or interface obliquely, producing radial spherical aberration. Longitudinal spherical aberration, by contrast, refers to axial focus errors along the optical axis for on-axis light, not specifically tied to oblique incidence. Coma describes off-axis blur with comet-like tails due to asymmetry of the system, and curvature of field is about the image plane not being flat. So the description fits radial spherical aberration best.

Radial spherical aberration is the one that arises when oblique incidence into a spherical surface causes rays at different radii to focus differently. When light enters at an angle, the astigmatic effect of oblique rays means paraxial and off-axis rays don’t converge in the same way, and this leads to focusing errors that depend on how far a ray is from the optical axis. In other words, the blur varies with radius because the rays hit the lens or interface obliquely, producing radial spherical aberration.

Longitudinal spherical aberration, by contrast, refers to axial focus errors along the optical axis for on-axis light, not specifically tied to oblique incidence. Coma describes off-axis blur with comet-like tails due to asymmetry of the system, and curvature of field is about the image plane not being flat. So the description fits radial spherical aberration best.