Strange Artifacts -


Wayne Hixson
 

I was imaging NGC6888 (Crescent Nebula) and thought I'd discovered a new edge-on galaxy. I attach an extreme closeup. There are also fainter reflections both to the right and up. It appears in all the subs. I dithered the frames and when I blink them, it moves sort of with the stars but not always the same amount!! It's consistent enough though that it's obvious in the stacked image.

My imaging train is the AP130GTX, QuadTCC, Optolong L-eXtreme filter in a filter drawer, and the QHY268C camera. 

I've seen these with other filters so probably not related to the L-eXtreme. Figured this forum was a good place to find the expertise to diagnose the problem

Wayne


Wayne Hixson
 

Here's the stacked image showing artifact with three reflections


Robert Chozick
 

Due to the randomness I think it is satellites or meteors that you did not remove in processing.  Did you use some sort of standard deviation process in your stacking routine.  I always do whether I see anything in my subs or not.

Robert

On Sep 4, 2021, at 11:50 AM, Wayne Hixson via groups.io <wayneh9026@...> wrote:

Here's the stacked image showing artifact with three reflections <Artifact2.jpg>


Wayne Hixson
 

Hi Robert, I should have mentioned these appear on almost all the subs, so it doesn’t appear to be more random events like meteors. I suspect it’s reflections somewhere. 


Michael 'Mikey' Mangieri
 

It does appear to be some sort of reflection. I would check your image train and see if there are sections inside that are not painted black. 

It also appears that you are not in focus as the stars appear as halos. 


On Sep 4, 2021, at 2:06 PM, Wayne Hixson via groups.io <wayneh9026@...> wrote:

Hi Robert, I should have mentioned these appear on almost all the subs, so it doesn’t appear to be more random events like meteors. I suspect it’s reflections somewhere. 


Roland Christen
 

These kind of reflections always come from some part very close to the focal plane. They cannot originate further up towards the objective lens. Since they are straight lines, they probably originate from some straight part near the chip. I have seen something similar coming from the bottom of an off-axis prism that was refracting (not reflecting) a bright star into the focal plane (similar to diffraction from a Newtonian spider). If not that, then are you using square filters by any chance?

Remove the camera body and look up into the optical train and look down into the camera. Do you see any linear (straight line) obstructions at the edges?

Roland



-----Original Message-----
From: Wayne Hixson via groups.io <wayneh9026@...>
To: main@ap-gto.groups.io
Sent: Sat, Sep 4, 2021 1:06 pm
Subject: Re: [ap-gto] Strange Artifacts -

Hi Robert, I should have mentioned these appear on almost all the subs, so it doesn’t appear to be more random events like meteors. I suspect it’s reflections somewhere. 

--
Roland Christen
Astro-Physics


Wayne Hixson
 

Thanks Roland - I’ll bet it’s the OAG prism. I’ll take a look. 


On Sep 4, 2021, at 11:48 AM, Roland Christen via groups.io <chris1011@...> wrote:


These kind of reflections always come from some part very close to the focal plane. They cannot originate further up towards the objective lens. Since they are straight lines, they probably originate from some straight part near the chip. I have seen something similar coming from the bottom of an off-axis prism that was refracting (not reflecting) a bright star into the focal plane (similar to diffraction from a Newtonian spider). If not that, then are you using square filters by any chance?

Remove the camera body and look up into the optical train and look down into the camera. Do you see any linear (straight line) obstructions at the edges?

Roland



-----Original Message-----
From: Wayne Hixson via groups.io <wayneh9026@...>
To: main@ap-gto.groups.io
Sent: Sat, Sep 4, 2021 1:06 pm
Subject: Re: [ap-gto] Strange Artifacts -

Hi Robert, I should have mentioned these appear on almost all the subs, so it doesn’t appear to be more random events like meteors. I suspect it’s reflections somewhere. 

--
Roland Christen
Astro-Physics


Wayne Hixson
 

I think the OAG prism is the problem. The prism is extended quite a way into the optical path. Also, the bottom edge of the prism is not quite parallel to the long edge of the chip. It was rotated 5 degrees or so which would extend the corner of the prism on one side even further into the optical train. I’ve adjusted both and will check it out when I get clear skies again. 

Thanks!

Wayne


On Sep 4, 2021, at 12:06 PM, Wayne Hixson via groups.io <wayneh9026@...> wrote:

Thanks Roland - I’ll bet it’s the OAG prism. I’ll take a look. 


On Sep 4, 2021, at 11:48 AM, Roland Christen via groups.io <chris1011@...> wrote:


These kind of reflections always come from some part very close to the focal plane. They cannot originate further up towards the objective lens. Since they are straight lines, they probably originate from some straight part near the chip. I have seen something similar coming from the bottom of an off-axis prism that was refracting (not reflecting) a bright star into the focal plane (similar to diffraction from a Newtonian spider). If not that, then are you using square filters by any chance?

Remove the camera body and look up into the optical train and look down into the camera. Do you see any linear (straight line) obstructions at the edges?

Roland



-----Original Message-----
From: Wayne Hixson via groups.io <wayneh9026@...>
To: main@ap-gto.groups.io
Sent: Sat, Sep 4, 2021 1:06 pm
Subject: Re: [ap-gto] Strange Artifacts -

Hi Robert, I should have mentioned these appear on almost all the subs, so it doesn’t appear to be more random events like meteors. I suspect it’s reflections somewhere. 

--
Roland Christen
Astro-Physics


Luca Marinelli
 

I had a very similar artifact from the edge of the Optec Sagitta OAG with a FLI ML16200 sensor. Moving the prism up the stalk away from the center of the sensor just a few mm took care of it. 

Luca 

On Sep 4, 2021, at 3:06 PM, Wayne Hixson via groups.io <wayneh9026@...> wrote:

 Thanks Roland - I’ll bet it’s the OAG prism. I’ll take a look. 


On Sep 4, 2021, at 11:48 AM, Roland Christen via groups.io <chris1011@...> wrote:


These kind of reflections always come from some part very close to the focal plane. They cannot originate further up towards the objective lens. Since they are straight lines, they probably originate from some straight part near the chip. I have seen something similar coming from the bottom of an off-axis prism that was refracting (not reflecting) a bright star into the focal plane (similar to diffraction from a Newtonian spider). If not that, then are you using square filters by any chance?

Remove the camera body and look up into the optical train and look down into the camera. Do you see any linear (straight line) obstructions at the edges?

Roland



-----Original Message-----
From: Wayne Hixson via groups.io <wayneh9026@...>
To: main@ap-gto.groups.io
Sent: Sat, Sep 4, 2021 1:06 pm
Subject: Re: [ap-gto] Strange Artifacts -

Hi Robert, I should have mentioned these appear on almost all the subs, so it doesn’t appear to be more random events like meteors. I suspect it’s reflections somewhere. 

--
Roland Christen
Astro-Physics


Wayne Hixson
 

That’s exactly the OAG I have too. 


On Sep 4, 2021, at 12:57 PM, Luca Marinelli <photo@...> wrote:


I had a very similar artifact from the edge of the Optec Sagitta OAG with a FLI ML16200 sensor. Moving the prism up the stalk away from the center of the sensor just a few mm took care of it. 

Luca 

On Sep 4, 2021, at 3:06 PM, Wayne Hixson via groups.io <wayneh9026@...> wrote:

 Thanks Roland - I’ll bet it’s the OAG prism. I’ll take a look. 


On Sep 4, 2021, at 11:48 AM, Roland Christen via groups.io <chris1011@...> wrote:


These kind of reflections always come from some part very close to the focal plane. They cannot originate further up towards the objective lens. Since they are straight lines, they probably originate from some straight part near the chip. I have seen something similar coming from the bottom of an off-axis prism that was refracting (not reflecting) a bright star into the focal plane (similar to diffraction from a Newtonian spider). If not that, then are you using square filters by any chance?

Remove the camera body and look up into the optical train and look down into the camera. Do you see any linear (straight line) obstructions at the edges?

Roland



-----Original Message-----
From: Wayne Hixson via groups.io <wayneh9026@...>
To: main@ap-gto.groups.io
Sent: Sat, Sep 4, 2021 1:06 pm
Subject: Re: [ap-gto] Strange Artifacts -

Hi Robert, I should have mentioned these appear on almost all the subs, so it doesn’t appear to be more random events like meteors. I suspect it’s reflections somewhere. 

--
Roland Christen
Astro-Physics


Eric Claeys
 

I would bet it’s reflections off some straight surface.  Satellites will usually be much longer.  Meteors tend to be dim on one end and bright on the other, and wider where they are brighter.

It looks like the artifacts on the right are brighter than the ones on the left, as if they are dimmer the farther away from a light source.  If you have a bright light source on the left, are the artifacts on the right dimmer than the ones to the left?

 

Eric