Weird stars

that_guy (Tony) · #1 20-03-2018, 10:00 PM

Hey gang, just stacked some images from this saturday at watts bridge. I decided to try some more vague and not that well known target (for me anyways) since my guiding was by far my personal best. These were 10 minute exposures but when I stacked them, on one side, it sort of has a 3d effect where one colour seems to have shifted slightly, it actually hurts my eyes if i look at it for too long. Anyone know what could cause this effect? If so how do I get rid of these literal eyesores. The rest of the image seems fine, its just on the right side that seems to be effected (gradually getting worse as it approaches the edge. I've attached the full image as well as a 100% crop of one of affected side.
full res image here

billdan (Bill) · #2 20-03-2018, 10:18 PM

Hi Tony,

I had a similar effect with my QHY12 OSC camera, though in my case it was the blue that was out of alignment.
I asked the question on the Startools forum what was happening and I was told it is a stacking artifact or debayering artifact that only occurs with OSC cameras.
Fortunately Startools has a module called "Lens", where you can move the red or blue pixels left/right or up/down, to get them into alignment. This fixed the problem for me.

EDIT: Your problem could be different if its only happening towards the edge, mine happened across the whole frame.

Cheers
Bill

Slawomir (Suavi) · #3 21-03-2018, 06:38 PM

Hi Tony,

It looks like a sensor tilt to me, with the top right corner either being too close or too far. I suspect you are using a doublet, which would emphasise the tilt, so the corner that is out of focus would have stars with slightly shifted positions and would vary is size in different channels (RGB).

that_guy (Tony) · #4 21-03-2018, 08:43 PM

I'm using a triplet. I haven't had any issues like this before. I'm thinking maybe the camera wasn't securely tightened and slacked on an angle on the focuser. Can that cause this?

Bart · #5 21-03-2018, 09:36 PM

I think it is a registration/star alignment issue when you are preparing them to be stacked. I have noticed it some times in my images and when I go back and take more time calibrating and registering them, the problem goes away.

Slawomir (Suavi) · #6 22-03-2018, 06:37 AM

Quote:

Originally Posted by that_guy

I'm using a triplet. I haven't had any issues like this before. I'm thinking maybe the camera wasn't securely tightened and slacked on an angle on the focuser. Can that cause this?

Yes, I believe this could be the cause of tilt that leads to star misalignment in part of the image.