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Reflection Artifacts in the ASI6200

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#226 AtmosFearIC

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Posted 18 September 2020 - 09:08 PM

I don’t have access to my files but I am getting the ((o)) artefact with a QHY183M, RH200 and 3nm 36mm Astrodons.
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#227 rockstarbill

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Posted 18 September 2020 - 09:09 PM

I don’t have access to my files but I am getting the ((o)) artefact with a QHY183M, RH200 and 3nm 36mm Astrodons.

Interesting, any chance you can flip the filter? Not that I think it will do anything but to keep things consistent.

 

For those unaware, RH scope designs do NOT use a spider, but do have a central obstruction (secondary). 


Edited by rockstarbill, 18 September 2020 - 09:10 PM.


#228 AtmosFearIC

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Posted 18 September 2020 - 09:58 PM

Interesting, any chance you can flip the filter? Not that I think it will do anything but to keep things consistent.

For those unaware, RH scope designs do NOT use a spider, but do have a central obstruction (secondary).


Should be able to, I have all the filters facing the same way according to the writing.
https://www.astrobin.../full/aoy490/0/

This has been quite heavily processed but does show it a bit.

#229 rockstarbill

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Posted 18 September 2020 - 09:59 PM

So based on provided data, the ((o)) issue has been observed on the following cameras:

  1. ASI6200MM-Pro
  2. ASI183MM-Pro
  3. ASI294MM-Pro
  4. ASI1600MM-Pro
  5. QHY183M
  6. QSI583 WSG
  7. FLI ML8300 (BK7 Windows Glass)
  8. Whatever the Hubble uses lol.gif

It has not been observed on the following cameras:

  1. FLI ML16200
  2. FLI ML8300 (Post Window Change to F116 Glass)
  3. QHY 600M (Thanks Ross!)

Not only did the QHY600 not show the ((o)) pattern, it did not show the small-scale halo, and did not show the grid artifact, at 20 minutes HA with 52 Cyg (Mag 4) on-axis at the center of the frame. Gamma Cyg (Sadr) is Mag 2, so its not a perfect test of the grid pattern issue (as its not the same star) but its not likely to be an issue. Scope for the QHY600 ws a 12.5 Planewave CDK. One important thing to call out, that Ross brought to my attention -- the Chroma filters he uses are 5nm and not 3nm.

 

Link to data from Ross (rgsalinger) -  CDK 12.5 + QHY600M + Chroma 5nm HA - 20 mins, 52 Cyg:

https://drive.google...iew?usp=sharing

 

The FLI ML8300 showed that pattern and a small scale halo and was sent back to FLI to have the BK7 glass replaced with F116. After the change, the halo and the ((o)) were gone. The FLI ML16200 has never shown that issue, but came with F116 glass out of the box.

 

Since QSI is not around it will be hard to determine what substrate they used, but given the era of those 500 series cameras it was likely BK7 as well. BK7 is the same glass used in the ZWO cameras (K9 is what the China sourced equivalent is called) and all of the cameras with BK7 or K9 exhibit the ((o)) and/or small-scale halo problem. I dont know what the 183M (or 600M for that matter) use. So if someone does or can find out that would be an interesting data point to have.


Edited by rockstarbill, 19 September 2020 - 07:21 AM.

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#230 rockstarbill

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Posted 18 September 2020 - 10:19 PM

Should be able to, I have all the filters facing the same way according to the writing.
https://www.astrobin.../full/aoy490/0/

This has been quite heavily processed but does show it a bit.

I do see it, some of the processing has shielded the image from the effect but it is clearly there and in the subs I am sure it was very visible. There is a strong data correlation (note: not causation) to 3nm narrowband filters and larger optical systems. Flipping the filter worked for the SCT, so you may want to try that and see what the result is.



#231 sharkmelley

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Posted 19 September 2020 - 12:34 AM

I don't agree it's Airy rings for the reason I outlined in post #62.

I have a really off the wall idea, a wild conjecture.  

 

The concentric rings ((o)) really do look like Airy rings, don't they?  It's because they are equally spaced.  A pattern such as Newton's Rings or Fabry-Perot has rings that become more closely spaced when further from the centre.

 

Let's suppose the optics and seeing conditions are good enough to produce a excellent set of closely spaced Airy rings i.e. more closely spaced than the pixel pitch of the sensor.  What would happen if those rings were then sampled by the sensor - would there be a beat frequency producing a pattern with spurious resolution and would this spurious resolution pattern look like regularly spaced rings?

 

Mark


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#232 AtmosFearIC

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Posted 19 September 2020 - 12:55 AM

I have a really off the wall idea, a wild conjecture.

The concentric rings ((o)) really do look like Airy rings, don't they? It's because they are equally spaced. A pattern such as Newton's Rings or Fabry-Perot has rings that become more closely spaced when further from the centre.

Let's suppose the optics and seeing conditions are good enough to produce a excellent set of closely spaced Airy rings i.e. more closely spaced than the pixel pitch of the sensor. What would happen if those rings were then sampled by the sensor - would there be a beat frequency producing a pattern with spurious resolution and would this spurious resolution pattern look like regularly spaced rings?

Mark


My RH200 suffers from various aberrations, pretty bad SA and trefoil astigmatism, I doubt it would be detecting the airy rings.
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#233 bugbit

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Posted 19 September 2020 - 01:08 AM

I have a really off the wall idea, a wild conjecture.  

 

The concentric rings ((o)) really do look like Airy rings, don't they?  It's because they are equally spaced.  A pattern such as Newton's Rings or Fabry-Perot has rings that become more closely spaced when further from the centre.

 

Let's suppose the optics and seeing conditions are good enough to produce a excellent set of closely spaced Airy rings i.e. more closely spaced than the pixel pitch of the sensor.  What would happen if those rings were then sampled by the sensor - would there be a beat frequency producing a pattern with spurious resolution and would this spurious resolution pattern look like regularly spaced rings?

 

Mark

Not too odd of a thought. I flashed on harmonics from the photons arriving in a wave form that were out of sync from the timing of the exposure. Similar to a timing light on a vehicle.


Edited by bugbit, 19 September 2020 - 01:11 AM.


#234 rockstarbill

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Posted 19 September 2020 - 07:22 AM

It is very interesting that ALL of the ZWO mono cameras used for deep sky imaging are showing the ((o)) issue except for the 178MM-Cool. Need to go look around and see if anyone has used that and ran into the same issue.



#235 rockstarbill

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Posted 19 September 2020 - 07:32 AM

I have a really off the wall idea, a wild conjecture.  

 

The concentric rings ((o)) really do look like Airy rings, don't they?  It's because they are equally spaced.  A pattern such as Newton's Rings or Fabry-Perot has rings that become more closely spaced when further from the centre.

 

Let's suppose the optics and seeing conditions are good enough to produce a excellent set of closely spaced Airy rings i.e. more closely spaced than the pixel pitch of the sensor.  What would happen if those rings were then sampled by the sensor - would there be a beat frequency producing a pattern with spurious resolution and would this spurious resolution pattern look like regularly spaced rings?

 

Mark

Good points here, Mark. I am curious if those that flipped their filters to "solve" the ((o)) issue, just had their seeing worsen since their experience with that artifact and assumed that the filter flip solved the problem -- when in reality the sky conditions changed and the issue was no longer noticable. I do see a correlation in my data to the ((o)) issue showing up and changes in sky quality. 


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#236 Lead_Weight

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Posted 19 September 2020 - 07:33 AM

I looked for FLI ML16200 images but only saw them used with refractors. I just think there’s a lot more ZWO cameras out there making it easier to find examples. So I wouldn’t rule out the other cameras being free from this issue.
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#237 rockstarbill

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Posted 19 September 2020 - 07:37 AM

I looked for FLI ML16200 images but only saw them used with refractors. I just think there’s a lot more ZWO cameras out there making it easier to find examples. So I wouldn’t rule out the other cameras being free from this issue.

Ive used the FLI 16200 with a 10" RCOS RC scope and did narrowband with it. Let me try and find those frames. It does not show the problem at all.

 

Edit: I no longer seem to have those shots. I will need to take new ones when my 16200 gets back from its 5 year maintenance work at FLI.

 

Here is some narrowband data from the 8300 I talked about, after its window was changed (to the same glass in the ML16200), with the 10" RCOS. 

 

https://www.astrobin.../full/jfa3vh/C/

 

While I get that there are a lot of ZWO cameras out there. That does not explain why the QHY600 was free of all of these effects. Even the ((o)) issue and small-scale halo, which some people have said are "normal" in other discussions I have had about this issue. Be sure to look at the 20 min frame Ross contributed to the discussion. It is pretty telling.


Edited by rockstarbill, 19 September 2020 - 07:51 AM.


#238 vakulenko_sergiy

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Posted 19 September 2020 - 08:01 AM

I have a really off the wall idea, a wild conjecture.  

 

The concentric rings ((o)) really do look like Airy rings, don't they?  It's because they are equally spaced.  A pattern such as Newton's Rings or Fabry-Perot has rings that become more closely spaced when further from the centre.

 

Let's suppose the optics and seeing conditions are good enough to produce a excellent set of closely spaced Airy rings i.e. more closely spaced than the pixel pitch of the sensor.  What would happen if those rings were then sampled by the sensor - would there be a beat frequency producing a pattern with spurious resolution and would this spurious resolution pattern look like regularly spaced rings?

 

Mark

+1 for idea.

 

Those (o) artifacts remind me a laser beam from my Glatter collimator (when you look closely to the dot produced by it). As I remember laser is coherent and monochromatic.

 

Another factor that this (o) ring issue observable only with 3nm narrowband filters.

 

Seems that those two factors correlates there. So 3nm filter may produce enough coherent and monochromatic light to produce same artifact as laser beam.


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#239 rockstarbill

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Posted 19 September 2020 - 08:09 AM

+1 for idea.

 

Those (o) artifacts remind me a laser beam from my Glatter collimator (when you look closely to the dot produced by it). As I remember laser is coherent and monochromatic.

 

Another factor that this (o) ring issue observable only with 3nm narrowband filters.

 

Seems that those two factors correlates there. So 3nm filter may produce enough coherent and monochromatic light to produce same artifact as laser beam.

Good post. waytogo.gif

 

Its likely the 3nm makes the effect occur more frequently, as it will block more unwanted light. There are cases where 5nm filters have shown the same problem. Then there is the new data from the 12.5 PW and the QHY600M-PE that do not show any of the symptoms talked about in this thread at all. No grid, no ((o)), no small-scale halo. 

 

I dont know what Ross' seeing is like in general or on that night though. Could be a factor...  



#240 GeneralT001

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Posted 19 September 2020 - 08:23 AM

Well for whats its worth, heres my recent Crescent with Chroma 3nm Ha and OIII with the ML16200 and the C11 Edge. Not the brightest stars but no sign of the issue that I can see:

 

OIIandHa.JPG

 

https://1drv.ms/u/s!...srZGG6c?e=XSBMy

 

lhttps://1drv.ms/u/s!...0-y3-w?e=mNMJ6Z


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#241 rockstarbill

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Posted 19 September 2020 - 04:24 PM

The window out test will be tonight. It's not me doing the test, Monkeybird747 is the brave warrior taking on that challenge.
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#242 Ken82

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Posted 19 September 2020 - 07:09 PM

Interesting I did get this strange artefact when using a baader 7nm filter and my fsq 85 + 6200.
 

At this time i didn’t have the correct adapters for either my 85 or 106 so the 6200 was connect via 2” nosepiece causing considerable tilt (as you can see from elongation in image)

 

I had initially put it down to the filter and tilt so shortly changed to chroma which solved the issue.

ken 

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#243 rockstarbill

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Posted 19 September 2020 - 07:15 PM

Interesting I did get this strange artefact when using a baader 7nm filter and my fsq 85 + 6200.

At this time i didn’t have the correct adapters for either my 85 or 106 so the 6200 was connect via 2” nosepiece causing considerable tilt (as you can see from elongation in image)

I had initially put it down to the filter and tilt so shortly changed to chroma which solved the issue.
ken


If you can, point to Sadr and take a 15 minute exposure in HA and post up the sub. Would be good to see.

 

Refractors have had a way less chance of showing these problems. Not a zero chance, but it seems the larger reflector/cassegrain scopes are more prone to getting this to appear.


Edited by rockstarbill, 19 September 2020 - 09:11 PM.


#244 rockstarbill

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Posted 19 September 2020 - 10:52 PM

Glass off results:

  • Sensor window is not causing (nor preventing) the large scale grid pattern. This was expected. (See below for an interesting observation using Mark's script) 
  • Halos on less bright stars were still present, but may be diminished with the sensor glass removed. The glass back on test is going to happen shortly to determine.
  • The ((o)) effect was not present at all with the sensor glass off. Next step is to confirm with the glass on.
  • Bright out of focus star showed a very tight cluster of very small circles, around the radius of a bright star (Vega in this case). This is something we noted when checking the focus of the telescope prior to running any actual tests. We were not looking for this, but found it. 

Data will be available later, we are optimizing sky time at the moment. 

 

The interesting observation about the grid was that the optimum fit for Mark's script was at 20mm vs 23mm, suggesting that the grid pattern was now being caused by the same side of the filter, but that side after a flip had moved 3mm closer (since the filter is 3mm thick). This strongly suggests that the filter is the cause of the grid pattern, and that the cause of it is the AR coated side of the filter. Flipping the filter does not solve the problem, rather it moves it closer to the sensor, and in the testing we had to use brighter stars or stars with less nebulosity than Sadr has in its FOV to detect it. 


Edited by rockstarbill, 20 September 2020 - 12:23 AM.

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#245 GeneralT001

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Posted 19 September 2020 - 11:15 PM

Not that I am getting any reflection artifacts that this post discusses - but I did pull my OIII Chroma 3nm filter out, to have a look at, and the reflective side was most definitely pointing towards the telescope side and not the camera side. I will install it with the reflective coating towards the camera and see if this helps with my OIII data - because I just used it - for the first time - on the Crescent nebula - and the OIII data truly sucked!


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#246 rockstarbill

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Posted 19 September 2020 - 11:16 PM

Not that I am getting any reflection artifacts that this post discusses - but I did pull my OIII Chroma 3nm filter out, to have a look at, and the reflective side was most definitely pointing towards the telescope side and not the camera side. I will install it with the reflective coating towards the camera and see if this helps with my OIII data - because I just used it - for the first time - on the Crescent nebula - and the OIII data truly sucked!

Was the HA oriented the opposite way than the OIII was found to be in? 



#247 GeneralT001

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Posted 19 September 2020 - 11:23 PM

Was the HA oriented the opposite way than the OIII was found to be in? 

Yes, the Ha was also in "backwards" with the reflective side pointing towards the scope. I wasn't overly happy with the Ha data as well. So I will be curious to see if the data looks any better with those too flipped - mind you I will be trying it on the Planewave 12.5 - if the wx ever permits :)


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#248 GeneralT001

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Posted 19 September 2020 - 11:36 PM

I'm no optical engineer...but you would think that the very obvious coating difference on each side of the OIII and Ha filter would have an effect - no matter what Chroma claims?? How can it not with one side like a mirror and the other clear?



#249 rockstarbill

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Posted 19 September 2020 - 11:53 PM

I'm no optical engineer...but you would think that the very obvious coating difference on each side of the OIII and Ha filter would have an effect - no matter what Chroma claims?? How can it not with one side like a mirror and the other clear?

I just pulled and tested an Astrodon filter and they have the same differences that the Chroma filters do. They are NOT the same on both sides.


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#250 Peter in Reno

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Posted 19 September 2020 - 11:53 PM

I thought it was suggested the reflective side of the filters point to the telescope so that there's no refections between the filters and camera's sensor. 

 

Peter 




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