What is the lens aberration that causes a shorter focal length for rays near the edge of the lens?

• A. Chromatic aberration
• B. Distortion
• C. Spherical aberration
• D. Pincushion effect

Answer: (C)

Spherical aberration occurs when rays of light that pass through the edges of a spherical lens focus at a different point than those that pass near the center. This phenomenon is due to the shape of the lens itself—spherical lenses do not focus light rays uniformly. As a result, rays that enter closer to the edge of the lens are bent more sharply, causing them to converge at a shorter focal length compared to those that pass through the central area.

In practical terms, spherical aberration can lead to a blurred image, particularly in lenses that are not specifically designed to correct for this type of aberration. Understanding spherical aberration is important in fields involving optics, such as photography, astronomy, and various engineering applications, because it highlights the need for lens design that minimizes these aberrations to enhance image quality.