The primary optical aberration of fast Newtonian telescopes is the so-called coma, where stars near the edge of the field of view are not point-like but increasingly elongated. This can be visually disturbing, especially in systems with an f/5 or faster focal ratio, but it becomes a significant issue during astrophotography. The solution is a coma corrector that can be placed in the eyepiece holder, among which the TeleVue ParaCorr Type-2 coma corrector far surpasses its competitors.
The Paracorr is highly effective in eliminating the coma of Newtonian telescopes, up to an F/3 focal ratio. Thus, both in visual and photographic observations, perfect, point-like stars can be seen even at the edge of the field of view. A major advantage of the TeleVue coma corrector is that it does not introduce any harmful aberrations (e.g., chromatic aberration, spherical aberration) to the image, and the light transmission is not noticeably reduced. It extends the telescope's focus only slightly, by about 15%, and can be used with both 1.25" and 2" eyepieces.
For astrophotography, the corrector can be used by unscrewing the eyepiece extension. It perfectly projects onto APS-C sized sensors (e.g., Canon EOS cameras) even in telescopes with an f/3 focal ratio. Its ideal sensor distance is approximately 55 mm. The image sharpness remains perfect across the entire field of view, free from spherical aberration and chromatic aberration, and there are no distorted stars at the edge of the field of view. Additional M48 or T2 adapters are required for camera attachment.
