Photography Stack Exchange is a question and answer site for professional, enthusiast and amateur photographers. It only takes a minute to sign up.
Sign up to join this community
When processing an astro-images taken with a Canon 450D and prime focus, I often end up with a series of faint circles radiating outwards from an off centre point. What are they and how do I get rid of them. I can hide them by darkening the background, but by doing that I then lose some of the detail in the distant galaxies.
Here is a link to my local astro-society. And here is the image:
This looks to me like Newton's rings, an interference pattern that occurs from closely-placed surfaces. They are usually only visible when narrow-band filters are used, or when the light is inherently narrow-band. With wide-band illumination, the rings fall in different places for the different wavelengths of light, so the effect is largely canceled out.
My best guess would be that, in your case, the rings are coming from the various parts of the sensor assembly. I'm not sure how the 450D is arranged, but there's likely an anti-aliasing (AA) filter, IR-blocking filter, and the sensor itself—all flat surfaces in close proximity that could give rise to Newton's rings.
These circles could be glare. This often happens if you have a light source hitting the front element of the lens from outside the image circle.
To prevent it use a lens hood.
It could also be light leakage in the telescope + camera assembly.
