Diagnose 08 of 29 Acquisition quality
Coma
Stars stretch outward from the center, more toward the edges, flaring like seagulls. The center is sharp.
- At 100 %
Edge stars each point away from the center of the frame with a flared tail. The effect grows steadily from the center to the edge.
- Causes, most likely first
No coma corrector on a fast Newtonian
A fast Newtonian has coma away from the center of its field by design. Without a corrector, every frame shows it.
FixFit a coma corrector suited to the scope, at the spacing its maker gives.
Rig Reality CheckCorrector spacing wrong
A coma corrector works at one distance from the sensor. Off that distance, some coma remains in the corners.
FixWork out the spacing with the whole train counted, filters included.
Backfocus Solver
- Looks like, but isn't
With a corrector fitted, symmetric corner distortion is its spacing. With none, on a Newtonian, it is coma.
Field rotation curves stars around a point. Coma stretches them straight out from the center.
Elongated stars are stretched the same way across the whole frame, the center included.
Field curvature
Field curvature leaves corner stars round but bloated while the center is sharp. Coma stretches them.
- One frame can't tell you
One frame shows coma clearly. With a corrector fitted, it cannot say whether the spacing is long or short; change it and compare.
- How to confirm the fix
Edge stars as round as the center in a focused sub.
- Sources
No outside source is cited here. The signature, the causes and their order are the atlas’s own, from imaging experience. The order is a judgment of likelihood; no measured frequency is behind it.
In the symptom picker
- Stars stretch outward from the center, more toward the edges, like seagullsweight 3
- Corner stars are triangles or little comets while the center is sharpweight 2
Tools for this
Last updated All 29 failure modes, and the symptom picker