If you flatten the base curve of a spherical lens, what would the optics look like?

• A. Sharp in the center & blurry in the periphery
• B. Blurry in the center & sharp in the periphery
• C. Uniformly sharp
• D. Astigmatic blur

Answer: (A)

Spherical aberration is the key idea here. A spherical lens tends to bend light differently for rays that strike near the center compared with rays that hit toward the edge. When you flatten the back (base) curve, the lens becomes less curved overall, and this change affects off‑axis (peripheral) rays more than axial (central) rays. As a result, the central rays still focus fairly well on the retina, but the peripheral rays fail to come to the same focus, producing blur toward the edges. That gives a sharp center with a blurred periphery.

The other possibilities don’t fit this pattern. Uniform sharpness would require correcting spherical aberration across the entire pupil, which a flattened back surface does not provide. Astigmatic blur would show different focusing in different meridians, not simply center-versus-edge blur. And peripheral sharpness isn’t expected when the back surface is flattened in a spherical lens.