This Sky-Watcher Quattro Coma Corrector is an optical accessory you will appreciate if you wish to do astroimaging with your f/4 Quattro imaging Newtonian scope. All classical Newtonian telescopes suffer from some coma problems because they have only a single parabolic mirror which does all of the ray focusing work! This is fundamental to the optical principles involved.
Coma is an optical aberration which is usually observed in off-axis images formed by a telescope with a parabolic focusing system. Stars located off-axis or near the edges of the field seem to have a comet-like appearance instead of being round. Astronomers who do mainly visual observing can usually overlook some coma in their field. But when you do astroimaging with your equipment, coma will become a nuisance rather quickly as you expect your stellar images to appear round or pointed. For best results with your f/4 Quattro Imaging Newtonian scope, use the Sky-Watcher Quattro Coma Corrector to completely eliminate that annoying coma aberration.
This Quattro coma corrector by Sky-Watcher is made with FPL51 and Schott glass and therefore features extra low dispersion imaging performance. The use of the Quattro Coma Corrector requires 55 mm of back focus and an image cone with an f/4 focal ratio because of its inherent design. Sky-Watcher makes Canon EOS and Nikon DSLR adapters for this purpose, and these can be obtained from OPT.