Can't source these rings in my images.

[FiveByEagle]

Hello!

Was finally able to complete the replacement of the primary cell of my AT130EDT and all of my chromatic aberrations have disappeared, but now its time to tackle issue #2.

I get wild vignettes in my integrations regardless of filter and I can not seem to source them. 

Initially I had thought it was caused by bad filters, so I exchanged filters and reversed them too. No real change there, and in my filter-less star tests since getting the new primary have really showed me that the filter/corrector is not the cause.

I am at a bit of a loss as to what is causing these and would LOVE to have some help on this. 

Could it be light spill? I noticed it is dark and light on the sides.. could this be tilt too? 

I have attached a few images -  the first is the single sub. second is the raw stack, third is after DBE, and then there is the master flat and final for inspection too.

Thank you!

 

 

Edited February 21, 2022 by FiveByEagle

[Ian McCallum]

Looks like the dreaded 'dust bunnies'!🤔

[FiveByEagle]

29 minutes ago, Ian McCallum said:

Looks like the dreaded 'dust bunnies'!🤔

Not those - the one BIG ring.

[Budgie1]

Yep, looks like dust particles close to the camera sensor. Check the camera sensor window and try a careful clean if you can see spots of dust on there.

Normally these are on the sensor window or any filters but if you have a focal reducer or field flattener in the image train, that would also be worth checking.

[Budgie1]

2 minutes ago, FiveByEagle said:

Not those - the one BIG ring.

That's called Vignetting.

[FiveByEagle]

52 minutes ago, Budgie1 said:

That's called Vignetting.

That is what I called it in my post though? 

[Budgie1]

30 minutes ago, FiveByEagle said:

That is what I called it in my post though? 

In my link it describes four causes; mechanical, optical, natural & pixel vignetting. Yours is more likely to be one of the first two.

Starting with mechanical, what size of filter are you using and are they/it in a filter wheel, filter draw or screwed into the image train somewhere? It would also be handy to know the camera make/model or sensor size and whether a field flattener or focal reducer is being used (or is this the corrector you mention)?

When you did the filter-less star test, how did you do this? Did you just remove the filter or was anything else removed from the image train and, if so, was the back spacing maintained? 

[The Lazy Astronomer]

To my (admittedly untrained) eye, there isn't any obvious tilt in the image.

I'm not sure if my eyes are playing tricks on me, but I think I can see some remnants of the dust bunnies in the calibrated image, which would lead me to believe flat correction is the issue. If you absolutely nuke the stretch on the calibrated master, does anything more obvious come to the fore?

[ONIKKINEN]

You get a ring like this when you move the camera between taking your lights and flats whether intentional or not.

Solutions to that problem: dont touch the camera before taking flats or fix the mechanical issue causing the movement. The mechanical issue i would assume to be in the focuser. I am not familiar with your scope but just looking at it online i see that the focuser looks pretty good so maybe not. Could also be some other adapter/thread or mechanical issue somewhere else in the scope. Basically your flats will only work if the entire optical train is exactly the same in your lights and flats, and if not you get these artifacts.

[Same old newbie alert]

What camera are you using? 

[FiveByEagle]

3 hours ago, Same old newbie alert said:

What camera are you using? 

Hello! 2600MC - 

[FiveByEagle]

10 hours ago, ONIKKINEN said:

You get a ring like this when you move the camera between taking your lights and flats whether intentional or not.

Solutions to that problem: dont touch the camera before taking flats or fix the mechanical issue causing the movement. The mechanical issue i would assume to be in the focuser. I am not familiar with your scope but just looking at it online i see that the focuser looks pretty good so maybe not. Could also be some other adapter/thread or mechanical issue somewhere else in the scope. Basically your flats will only work if the entire optical train is exactly the same in your lights and flats, and if not you get these artifacts.

100% I do believe that was my issue on an old rig, but on this new one flats are taken after PA but before the sequence, so focus should be identical.

I started doing this because of exactly what you said.

[Same old newbie alert]

19 minutes ago, FiveByEagle said:

Hello! 2600MC - 

Strange, as the spec says you can use a APS-C sized sensor

So what sized filters are you using?

The Astro-Tech AT130EDT triplet refractor allows imaging with a DSLR or CCD using an APS-C or equivalent sensor (29mm diagonal) with no vignetting. Adding the dedicated reducer/field flattener, #ATREDT30, will allow imaging with a full frame DSLR (43mm diagonal sensor) with only minor vignetting at the corners of the image.

[ONIKKINEN]

1 hour ago, FiveByEagle said:

100% I do believe that was my issue on an old rig, but on this new one flats are taken after PA but before the sequence, so focus should be identical.

I started doing this because of exactly what you said.

Hows the focuser then, any wiggleroom or unwanted movement if you try to grab the camera while its attached?

Focus position is less important, as long as its close it shouldn't matter this much.

[FiveByEagle]

3 hours ago, Same old newbie alert said:

Strange, as the spec says you can use a APS-C sized sensor

So what sized filters are you using?

The Astro-Tech AT130EDT triplet refractor allows imaging with a DSLR or CCD using an APS-C or equivalent sensor (29mm diagonal) with no vignetting. Adding the dedicated reducer/field flattener, #ATREDT30, will allow imaging with a full frame DSLR (43mm diagonal sensor) with only minor vignetting at the corners of the image.

Filters are all 2" - M42 OAG and M42 filter drawer.

[Same old newbie alert]

32 minutes ago, FiveByEagle said:

Filters are all 2" - M42 OAG and M42 filter drawer.

That's really strange as everything suggests that you shouldn't get any vignette

[FiveByEagle]

Just now, Same old newbie alert said:

That's really strange as everything suggests that you shouldn't get any vignette

Yep lol Bought everything specifically to avoid it actually...

I removed the camera to clean the sensor window, and that is when I saw that the edges of my focuser are not black but a reflective metal material. Might get a wax pen or something and cover that.

[adyj1]

29 minutes ago, FiveByEagle said:

Yep lol Bought everything specifically to avoid it actually...

I removed the camera to clean the sensor window, and that is when I saw that the edges of my focuser are not black but a reflective metal material. Might get a wax pen or something and cover that.

Did you notice anything obvious (dust, etc) on the sensor?

[FiveByEagle]

6 hours ago, adyj1 said:

Did you notice anything obvious (dust, etc) on the sensor?

Dust but that was it. Scopes are stored outside and I use a filter drawer, so there is an occasional opening to the air.