Comatic aberration is an optical aberration which mainly occurs with off-axis light fluxes. Comatic aberration is most serious when a microscope is out of alignment.
Comatic aberration is regularly considered as the most challenging and difficult aberration because of the asymmetry comatic aberration causes in an image. Cometic aberration is also one of the simplest aberrations to demonstrate.
Comatic aberration may be demonstrated with the use of a magnifying glass to focus the sun’s image and slightly tilt the magnifying glass about the principle rays from the sun on the sidewalk on a bright sunny day. When projected onto the concrete, the image of the sun will then stretches into a comet-like shape. This comet-like shape is a characteristic of comatic aberration.
Comatic aberration causes the production of a distinct shape exhibited by an image is due to the differences in refraction as the incident angle increases when rays of light pass through a number of lens zones.
Similar to spherical aberration, the severity of comatic aberration is strongly dependent upon the shape of the lens. A strongly concave positive meniscus lens will exhibit a substantial negative comatic aberration. Vice verse, a strongly convex meniscus lens will exhibit a significant positive comatic aberration. A plano-convex and bi-convex lens will produce comatic aberration ranging from slightly negative to zero.
The correction of comatic aberration involves the use of a combination of lenses which are positioned symmetrically around a central stop.