Prepare to be amazed at my lack of skill when it comes to diagnosing optical problems. I'm struggling with an imaging issue and I wonder if it's not collimation of my refractor...see the image below. All of my images are coming out with stars shaped like those shown. Here's what else I know from trying to diagnose it myself:
- I'm sure it's not poor tracking. The mount is an AP900, less than a year old and well polar aligned with 2" of periodic error.
- The image below is a 10 second image a few arc minutes from M1 when it was near the zenith.
- I see the same "flare" on stars when I put in an eyepiece and observe visually. If I go to the other side of focus - the rings look concentric to me - or very close - but the out of focus star is flattened along the opposite end. Using the image as an example...the bottom of the out of focus stars is flattened if I go to the other side of focus.
- The entire frame is this way, all in the same direction and all about the same amount of oblong shape. This doesn't change if I move to a different part of the sky.
- If I rotate the camera, the oblong stars will rotate as well - so I believe this rules out the camera, and confirms that it's the optical train itself.
- I don't believe it's astigmatism - as the "football" shape doesn't change its axis from one side of focus to the other.
Thanks for any help or assistance in diagnosing this issue.