Coma (optics)
In
coma) like a comet. Specifically, coma is defined as a variation in magnification over the entrance pupil. In refractive or diffractive optical systems, especially those imaging a wide spectral range, coma can be a function of wavelength, in which case it is a form of chromatic aberration
.
Overview
Coma is an inherent property of telescopes using
cometary coma
, hence the name.
Schemes to reduce coma without introducing spherical aberration include
Newtonian reflectors have been designed which reduce coma in newtonian telescopes. These work by means of a dual lens system of a plano-convex and a plano-concave lens fitted into an eyepiece adaptor which superficially resembles a Barlow lens.[1][2]
Coma of a single lens or a system of lenses can be minimized (and in some cases eliminated) by choosing the curvature of the lens surfaces to match the application. Lenses in which both spherical aberration and coma are minimized at a single wavelength are called bestform or aplanatic lenses.
In human vision
Vertical coma is the most common higher-order aberration in the eyes of patients with keratoconus.[3] Coma is also a common temporary symptom of corneal injuries or abrasions, in which case the visual defect gradually resolves as the cornea heals.
See also
References
- ^ a coma-correcting meniscus lens 4571036, Gebelein, Rolin J. & Shafer, David
- ^ Knisely, David (2004). "Tele Vue Paracor Coma Corrector for Newtonians" (PDF). Cloudy Nights Telescope Review. Retrieved 29 November 2010.
- PMID 17553566.