Fast Newtonian reflectors are popular for astrophotography because they gather a great deal of light quickly, but they naturally produce coma, an optical effect that stretches stars near the edges of the image into wedge or comet-like shapes. A coma corrector cancels this effect, producing round, pinpoint stars across the entire frame.
The Explore Scientific HR Variable Coma Corrector is designed for Newtonian telescopes and can be adjusted to match different focal ratios, with T2 threads for attaching DSLR, mirrorless and dedicated astronomy cameras. It also improves visual observing with wide-field eyepieces, sharpening stars toward the edge of the field. If you image with a Newtonian or a fast Dobsonian, a coma corrector is one of the most important accessories for achieving sharp, high-quality deep-sky astrophotography.
Coma becomes more noticeable as focal ratios get faster, so f/4 and f/5 Newtonians benefit most, especially when paired with larger camera sensors. To get the best results, set the correct spacing between the coma corrector and your camera sensor using T-rings and extension rings, then fine-tune with test exposures. Combined with a stable equatorial mount and good collimation, a coma corrector lets a fast Newtonian telescope produce sharp, wide-field images of nebulae and galaxies that rival much more expensive astrographs.
