Artifacts with M45 and Canon 6D

Hi all. Interesting to post to a forum sub with so few views and posts. Anyhoo, I managed 13x420s exposures of M45 through an AT6IN (Astro-Tech f/4 Newt)- but I have some artifacts and I'm trying to track down the cause of their appearance. I'd appreciate any help. I have used old flat frames- maybe that is an issue. Going to take fresh ones on this foggy morning.

Image can be found here at http://www.astrobin.com/309883/


Thank you for any input!

Best,

JN

Hi, Jacob. Those doughnuts look like the pupil of your scope way out of focus. Each one is coming from one bright star. The Palomar Schmidt images are loaded with those, in that case, light bouncing off the film, then off the flattish Schmidt Plate and back to the film... something like that. In your case... might be off a lens surface, camera window... Someone else may recognize this better. Richard Berry covers that stuff in his tome "Astronomical Image Processing." Tom

Thinking some more. If you count the pixels across the entire (little) doughnut, and multiply by the Pixel Pitch x F#... THAT is how far out of focus a bright star would be to create that. Sometimes the front-back bounce off a camera window can do that. OR even off the CCD chip, off the window and back. This is one reason CCD cams can be orederd without that little cover slip that is just forward of the chip. The general topic is "ghost images" and lotsa ways can get this. Depending, there may be not much to amend. Most often seen on BRIGHT stars. Tom