Coma (optics)

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 also a form of chromatic aberration.

The further off-axis (or the greater the angle subtended by the point with the optical axis), the worse this effect is.

Schemes to reduce coma without introducing spherical aberration include Schmidt, Maksutov, ACF and Ritchey–Chrétien optical systems.

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.

Coma of a single lens. Each cone of light focuses on different planes along the optical axis.
Coma of a single lens. Each cone of light focuses on different planes along the optical axis.
This is a comparison of the coma in an uncorrected f/3.9 Newtonian telescope versus the effects of coma with the Baader Rowe Coma Corrector.