Which specific lens aberrations does an aspheric lens help reduce?

• A. Chromatic aberration only
• B. Comatic aberration only
• C. Oblique astigmatism, distortion, spherical aberration
• D. Diffraction effects

Answer: (C)

Aspheric lenses are shaped to make how light is bent across the lens more uniform, which helps correct several off-axis and edge aberrations that spherical surfaces tend to introduce. Spherical aberration happens because rays at the edge don’t focus at the same point as central rays; by altering the curvature toward the edge, an aspheric surface brings those focal points closer together, reducing blur. Oblique astigmatism arises when off-axis rays don’t converge to a single sharp line; the aspheric design helps keep the sagittal and tangential focus closer, improving clarity for peripheral gaze. Distortion is about the change in magnification across the field, leading to pincushion or barrel effects; the varying curvature of an aspheric surface can keep magnification more consistent from center to edge, reducing distortion. Chromatic aberration, tied to wavelength-dependent dispersion of the lens material, isn’t corrected by shaping alone, so changing the surface won’t fix it. Likewise, diffraction is a wave-limit phenomenon that isn’t eliminated by lens geometry. So the combination of reduced oblique astigmatism, distortion, and spherical aberration is what an aspheric lens helps with.