What is Spherical Aberration?
Spherical aberration is a common optical defect in lenses and spherical mirrors where light rays striking the outer parts of the surface are focused at a different point than those striking closer to the center. Instead of a single, sharp focal point, light is spread out, leading to a blurred or distorted image.
How it Arises
This aberration occurs because the simple spherical shape of lenses and mirrors does not perfectly refract or reflect all parallel light rays to a single point. Rays further from the optical axis are bent or reflected more strongly than those closer to the axis, causing them to converge at different points along the axis.
Real-World Impact
In everyday photography, a camera lens exhibiting significant spherical aberration might produce images where fine details appear soft or hazy, especially at wider apertures where more of the lens's outer edges are used. Telescopes with spherical primary mirrors, like the Hubble Space Telescope before its repair, also suffer from this, making distant objects appear fuzzy.
Mitigating Spherical Aberration
Understanding spherical aberration is crucial in designing high-quality optical instruments. It is often minimized by using aspherical lenses, which have non-spherical surfaces designed to converge all light rays to a single focal point, or by combining multiple spherical lenses with different properties to cancel out the aberration.