A coma corrector is a corrective lens for Newtonian telescopes. This type of telescope can cause distortion of the image at the edge of the field of view, making stars look like little comets. This aberration is therefore called 'coma'. Delivers stunning wide-field views with pinpoint stars to the edge of the field. Optimised for all Sky-Watcher fast-ratio f/5 Newtonian Reflectors / Dobsonians, with 2” focuser. Does not alter magnification . Supplied complete with necessary adaptors for visual use. For imaging use with a DSLR camera, a suitable T-2 (M48x0.75) adaptor is required to match your camera.

Source:
https://www.astroshop.eu/flatteners-correctors-reducers/skywatcher-1-0x2-coma-corrector/p,18852