Which type of lens is typically used to correct for positive spherical aberration?

To correct for positive spherical aberration, an aspheric lens is the most effective choice. Positive spherical aberration occurs when light rays entering a lens near the edge focus at different points than those near the center, often causing a blurred image. The design of aspheric lenses features a gradual change in curvature, which allows them to manage how light is focused. This progressive curvature helps to align the focal points of light rays entering the lens from various positions, thereby minimizing aberrations and enhancing image clarity.

In sharp contrast, concave and convex lenses, while useful in other optical corrections, are not structured in a way that effectively addresses spherical aberration. Concave lenses diverge light rays, which does not assist in correcting positive spherical aberration, while convex lenses magnify and can exacerbate such aberrations due to their inherent spherical shape. Cylindrical lenses primarily correct for astigmatism, which is an entirely different optical issue related to variations in curvature in one dimension rather than the overall shape causing positive spherical aberration.