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  #1  
Old 04-12-2018, 09:15 AM
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What is this artifact in my images?

Hi, has anyone got any ideas what the artifact in my images is. This time it has appeared in the top right corner pointing of the witches head nebula, if I point in the other direction it is in the top left, so is in the same spot, I think. The thing is, it is not in all of my images and seems to only occur on long exposure when the scope is pointing high. Apart from dismantling my imaging train, I have checked for stray light, looked down the tube, etc.


PS: I think PixInsight might flip the image, might be in the other orientation??
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  #2  
Old 04-12-2018, 09:32 AM
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That looks like a reflection off a bright circular edge, so it could be a filter or an adapter/extension tube.
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  #3  
Old 04-12-2018, 09:33 AM
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Retrograde (Pete)
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Possibly an artefact due to the nearby star Beta Eridani?
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  #4  
Old 04-12-2018, 10:04 AM
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Stonius (Markus)
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I'd agree with what Pete said, from the angle of it. It seems to be coming from that direction.
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  #5  
Old 04-12-2018, 11:06 AM
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It's the bowshock of a hyper-space mothership. Repent!
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  #6  
Old 04-12-2018, 04:10 PM
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whzzz28 (Nathan)
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I had some similar issues awhile ago.

I never did find the culprit, but it was definitely in the image train - either the filters (number 1 suspect) or the camera.


Attached some similar issues I had. Also: http://core-au.net/astro/Collection/M78/100.jpg
Try removing all filters and taking a test shot to see if it still occurs.
My issue got worse and I ended up with lines/massive spikes through bright objects (mostly stars).
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  #7  
Old 04-12-2018, 09:31 PM
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Definitely a reflection. Most like a very bright star just outside the field of view and clearly where there is no baffle. What sort of OTA are you using?
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  #8  
Old 05-12-2018, 01:23 AM
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Id agree with previous comments about it being a reflection of a circular aperture within the image train. Take your camera off and look through the image train from where the camera would have been, while having the scope look into a dimly lit light source.



if you see light reflecting off surfaces, paint them flat black. I recently had this very issue... I did as I said above and it is now gone. In my case it was reflecting off of a black anodised adapter. So even black anodised adapters will cause this issue.


Josh
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  #9  
Old 05-12-2018, 08:02 AM
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Thanks for the thoughts on the issues, everyone. Originally I thought it was the neighbours lights then I realised it would be a glow on one side spreading across.

It is a William Optics FLT 132 that is baffled all the way down from memory, so possibly in the flattener or the filter wheel perhaps.

I'll try to get up there tonight and see if there is anything obvious.
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  #10  
Old 06-12-2018, 07:40 AM
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I went up to the obs last night although limited in what I could do and how long I could stay up there as I have work today and the flying ants were in plague proportions making any work with the light or monitor on extremely difficult.

I pulled the camera out and looked up the tube from the focuser end while pointed at the still daylight sky and it is all flat black and has about 4 baffle rings inside it.

From the objective end, all I can see is the focuser draw tube rack that is nicely chromed, the rest is all flat black and baffled. If I grab even a weak torch and shine it in there it is very reflective so I'm going to pull the focuser off and paint the rack flat black.

As for the filters etc, I will wait until some filters I purchased arrive and I have a Friday or Saturday night that lets me spend some time pulling off the camera and changing filters and removing them for test shots etc.

The LRGB filters are the Baader ones that have the arrows showing to point which way although they say to reverse them in certain circumstances. I might try that as well, other wise I have the original QHY ones to try back in as well.
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  #11  
Old 06-12-2018, 09:27 AM
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I have been getting a similar arcs when pointing in some directions, with help from another member here I had thought I had tracked it down to the edges on the shutter aperture of my dome, I thought it may have been light from a rather bright street light reflecting off the edges, I blackened them but a test still showed the arcs.

I then shone an averted light down the tube from the front and saw a major reflection coming off the front of the draw tube. The focuser is a Moonlite and the end of the draw tube is an anodised gloss black. I have taken the Moonlite off and now have the original Takahashi focuser fitted, it has a matt black end piece on the draw tube and I can't remember ever seeing these arcs from it.

Whilst I only did this yesterday, I haven't had a chance to test as yet due to clouds last night but I believe this to be the culprit and hopefully will be testing again tonight.

Sounds to me like you are having the same problem with an off-set star reflecting light off the end of the draw tube, I would think about taking the focuser off and blackening the end of the draw tube.

Cheers

John G
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  #12  
Old 07-12-2018, 07:19 AM
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Quote:
Originally Posted by JohnG View Post
I have been getting a similar arcs when pointing in some directions, with help from another member here I had thought I had tracked it down to the edges on the shutter aperture of my dome, I thought it may have been light from a rather bright street light reflecting off the edges, I blackened them but a test still showed the arcs.

I then shone an averted light down the tube from the front and saw a major reflection coming off the front of the draw tube. The focuser is a Moonlite and the end of the draw tube is an anodised gloss black. I have taken the Moonlite off and now have the original Takahashi focuser fitted, it has a matt black end piece on the draw tube and I can't remember ever seeing these arcs from it.

Whilst I only did this yesterday, I haven't had a chance to test as yet due to clouds last night but I believe this to be the culprit and hopefully will be testing again tonight.

Sounds to me like you are having the same problem with an off-set star reflecting light off the end of the draw tube, I would think about taking the focuser off and blackening the end of the draw tube.

Cheers

John G
Glad to hear you've got it sorted out mate.
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  #13  
Old 07-12-2018, 08:54 AM
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Hi,
I don't think it is this, but looks like that, Newton Rings:
https://en.wikipedia.org/wiki/Newton%27s_rings

Could come from two glass surfaces that are very close to each other.

Just an idea.

/Lars
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  #14  
Old 07-12-2018, 09:10 AM
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Quote:
Originally Posted by multiweb View Post
Glad to hear you've got it sorted out mate.
Thanks for the help mate, knew we would sort it sooner or later.

Turns out the arcs were from reflections of an off-set star off the end of the focuser tube. Original Takahashi focuser re-installed, no further problems.


Before and after shots, heavily stretched..

Cheers
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  #15  
Old 07-12-2018, 05:29 PM
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Thanks John, Lars, Marc and all. I will pull the focuser off and paint the rack rail flat black and see what happens. I have some filters coming so I will get the chance to open the filter wheel and check in there as well.
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  #16  
Old 08-12-2018, 07:50 AM
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What paint do you use for that?
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  #17  
Old 08-12-2018, 08:35 AM
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Was that to me Stonius?



I haven't painted yet although I have some Fiddly Bits or something from Bunning's that cost about $4.00 in flat black.
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  #18  
Old 08-12-2018, 08:48 AM
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Yes it was. I guess I'm just wondering what pain sticks to metal (primer required?) and is pproper matte.
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  #19  
Old 08-12-2018, 12:50 PM
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Yes it was. I guess I'm just wondering what pain sticks to metal (primer required?) and is pproper matte.
sand it first to roughen it then anything will stick. the aim is just to take the shine off. sometime just sanding is enough.
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  #20  
Old 08-12-2018, 03:33 PM
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Yes, not sure how it is going to go as it is chrome steel. Wasn't looking for a strip, rebuild and adjust but it's looking more like it the more I think about it.
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