Can't source these rings in my images.

James Ross:
What does your sensor face look like? It seems like there's a lot of dust on the camera window at the very least. How are you taking your flats? I can't really see the larger ring structure in the lights so maybe something is going slightly wrong with your flat calibration, or else DBE is getting it wrong - there is quite a strong gradient present in the raw sub so you have to get the DBE sample points correct.

Tilt I'd expect to show up as defocused stars in one or more quadrants of the image, not as this larger superimposed ring artifact.

Benny Colyn:
Guys, OP is not talking about the dust donuts. It's the under/over correction of the vignetting that this is about. 

I'm thinking either

• whatever is limiting your light cone has a little bit of reflection going on or
• your optical train - likely the focuser - has a some play causing the flats not to match 100% with the lights.

Andy Wray:
What was the ADU on your flat images?  Just wondering, because it looks like they are not compensating correctly when calibrating.

Benny Colyn:

Dan Vranic:

Benny Colyn:
Guys, OP is not talking about the dust donuts. It's the under/over correction of the vignetting that this is about. 

I'm thinking either

• whatever is limiting your light cone has a little bit of reflection going on or
• your optical train - likely the focuser - has a some play causing the flats not to match 100% with the lights.

Appreciate your reply man. I have posted this same question in 4 forums today and everyone has focused on the dust motes and are ignoring everything I am saying about my setup. Even had someone on CN get all high and mighty that I was not using a Newt right.... The AT130EDT is not a Newt lol.

When you say "limiting the light cone" what does that mean? I have a new flattener from a different company on the way to test out some theories too.

=> you may get better responses with the phrases "overcorrection" or "under correction". The "rings" isn't very clear unless you look deeper (by which time many have already hit "reply").

=> ultimately, something is constricting your light cone (from the objective lens to the sensor) and causing lesser illumination on the edges, it is unavoidable with any optics unless your image circle is severely oversized (at which point, I would rather say your sensor is too small and you are throwing away good part of your FoV, but I digress). With a quality APO, that usually should be the baffles in the OTA. Those are thin and should not reflect any light. But with a reducer, you often see (an edge of) the reducer becoming that limiting factor that cuts into the light cone and causes the "edge" on your masterflat. Or it can be the edge of a filter in your optical train. If those are shiny you end up with this. I had a very similar looking issue not too long ago. To cut a long story short, it was a bit of reflection likely from the filter mounting cell. Swapped those out for bigger, unmounted filters and both the vignetting decreased but also the "ring" went away. That's just an example, it could very well be the edge of your reducer/flattener or poor baffling in the OTA. Have a look down the OTA with everything mounted except the camera an check for anything that glitters when illuminated from the front (through the objective).

Great idea! I will give that a shot. There are baffles all the way down the tube I believe.

Benny Colyn:

Dan Vranic:

Benny Colyn:
Guys, OP is not talking about the dust donuts. It's the under/over correction of the vignetting that this is about. 

I'm thinking either

• whatever is limiting your light cone has a little bit of reflection going on or
• your optical train - likely the focuser - has a some play causing the flats not to match 100% with the lights.

Appreciate your reply man. I have posted this same question in 4 forums today and everyone has focused on the dust motes and are ignoring everything I am saying about my setup. Even had someone on CN get all high and mighty that I was not using a Newt right.... The AT130EDT is not a Newt lol.

When you say "limiting the light cone" what does that mean? I have a new flattener from a different company on the way to test out some theories too.

=> you may get better responses with the phrases "overcorrection" or "under correction". The "rings" isn't very clear unless you look deeper (by which time many have already hit "reply").

=> ultimately, something is constricting your light cone (from the objective lens to the sensor) and causing lesser illumination on the edges, it is unavoidable with any optics unless your image circle is severely oversized (at which point, I would rather say your sensor is too small and you are throwing away good part of your FoV, but I digress). With a quality APO, that usually should be the baffles in the OTA. Those are thin and should not reflect any light. But with a reducer, you often see (an edge of) the reducer becoming that limiting factor that cuts into the light cone and causes the "edge" on your masterflat. Or it can be the edge of a filter in your optical train. If those are shiny you end up with this. I had a very similar looking issue not too long ago. To cut a long story short, it was a bit of reflection likely from the filter mounting cell. Swapped those out for bigger, unmounted filters and both the vignetting decreased but also the "ring" went away. That's just an example, it could very well be the edge of your reducer/flattener or poor baffling in the OTA. Have a look down the OTA with everything mounted except the camera an check for anything that glitters when illuminated from the front (through the objective).

andrea tasselli:
Your focuser's end does not glint or sparkle. Don't know where that came from but it is not what's happening. If it were you would paint it over with black opaque paint. But it ain't yer problem.

andrea tasselli:
If you used proper flat technique any such thing, even if it existed, would be taken care by the flat. What the use of the flat if not for those instances?