Koma (optics)
Coming up Koma on the image of the Newtonian telescope without correction (left) and with Baader RCC equalizer Koma, comic aberration - one of the optical aberrations, ie the defects of optical systems. It consists of the fact that a beam of light rays coming from a point beyond the optical axis creates, after passing through the system, a dot-shaped or comet-shaped spot. The degree of distortion is the greater the farther away from the optical axis of the system is the light source. The telescope-free lens or system is called aplanate. This disorder may be caused by inaccuracy in the performance of the optical system or be closely related to its construction. For example, coma is a typical distortion for a parabolic mirror. wiki