Which type of Spherical aberration occurs when the Petzval surface does not correspond to the far point sphere of the eye?

Which type of Spherical aberration occurs when the Petzval surface does not correspond to the far point sphere of the eye?

• A. Longitudinal
• B. Radial
• C. Curvature of Field (Power Error)
• D. Distortion

Answer: (C)

When the Petzval surface does not line up with the eye’s far point sphere, the focus across the image field cannot lie on a flat plane. The Petzval surface describes how the focal surface bends due to lens design; if it doesn’t match the eye’s far point sphere, rays from off-axis points come to focus at different depths than those from the center. The result is an image that blurs more toward the edges because the best focus forms on a curved surface rather than the flat retina plane. This tendency is called curvature of field, also referred to as a power error in optical terms. It’s different from longitudinal spherical aberration, which is a shift of focus along the optical axis for rays at different apertures, or from distortion, which changes magnification with field position.

When the Petzval surface does not line up with the eye’s far point sphere, the focus across the image field cannot lie on a flat plane. The Petzval surface describes how the focal surface bends due to lens design; if it doesn’t match the eye’s far point sphere, rays from off-axis points come to focus at different depths than those from the center. The result is an image that blurs more toward the edges because the best focus forms on a curved surface rather than the flat retina plane. This tendency is called curvature of field, also referred to as a power error in optical terms. It’s different from longitudinal spherical aberration, which is a shift of focus along the optical axis for rays at different apertures, or from distortion, which changes magnification with field position.