Final answer:
Aberrations are defects in a lens or mirror that prevent light rays from converging at a single point, causing image distortion. Types include coma, spherical aberration, and astigmatism, with the latter also occurring in human vision, often corrected with prescription glasses.
Step-by-step explanation:
Aberrations occur when defects in a lens or mirror cause rays of light to fail to converge at a single focal point.
There are several types of aberrations, such as coma, which happens when different parts of a lens or mirror do not refract or reflect the image to the same point, resulting in a pear-shaped image. Another common type is spherical aberration, where rays converging from the outer edges of a lens converge to a focus closer to the lens, and rays closer to the axis focus further away. Astigmatism is an aberration that can occur in the lenses of the eyes, where rays passing through different regions focus at different distances, causing the image to appear elongated. Astigmatism is mostly due to irregularities in the shape of the cornea but can also be caused by lens defects or unevenness in the retina.
These defects can affect both manufactured lenses and the human eye, leading to issues like myopia (nearsightedness) and hyperopia (farsightedness), which often require vision correction through spectacles with the opposite irregularity to correct the problem.