What type of telescope requires a coma corrector for astrophotography?
The photo/visual Astro-Tech Coma Corrector is a three-part 2" auxiliary lens system that drastically reduces the coma and the curvature of field in a fast focal ratio Newtonian reflector during visual observing and astrophotography. It essentially makes an f/4 telescope perform like an f/8 in terms of coma.
What is the difference between a field flattener and a coma corrector?
For example: flatteners meant for SCTs (desired by photographers) are most often combined with a focal reducer (also desired by photographers). A coma corrector meant for a newtonian would bring the focal plane inside the focuser, making eyepieces unuseable.27 Mar 2018