14 replies to this topic

[slepage]

HI All,

 

I would like to have your input using the ASI 174mm for Ha imaging and if you had issues with Newton rings or inference bans.  Please let me know if this has been an issue for you too.

 

I just finished a exhaustive testing on what was causing my inference bans.   I did not have rings, but a section in the middle of the frame had straight bans. Everything was fine if the 174mm was used natively, but when I added either a 2.0 or 2.5x Barlow they appeared.  So, I set out to try and figure this out.  Here is the list of what I did and results that I got.

 

1) Rotate camera - No Change and the bans did not rotate with the changed camera position.

2) Tilt camera - No Change, This included many different degrees of tilt and rotation of tilt  - No Change and the bans did not rotate with the changed position.

3) Tilt Barlow and Rotate Barlow - No Change and the bans did not rotate with the changed position.

4) Rotate Diagonal/blocking filter - No Change and the bans did not rotate with the changed position.

5) Rotate DS unit - No Change and the bans did not rotate with the changed DS position.

        At this point I'm starting to think that it is something internal ( - Maybe between the two etalons???)

6) Changed the brand of Barlow - Was using a TeleVue 2.5x and switched to a Tak 2.0 Barlow.  - No Change but the bans were a little lighter - I believe this was do to the decrease in the barlow power.

7) Changed Camera to the ASI 290mm with the Tak and televue Barlow  - No BANS 

 

So After all that, I assume that it is the ASI 174 that was causing the issue.

 

I would love to hear comments on what I did and the results that I got, along with your success with using the ASI 174 and barlow combo.  If you use another camera of similar sensor size what is it and how is it working out for you.

 

The Image is the ASI174 w/ televue 2.5x Barlow. shows the bands

 

Thanks

Steve

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Edited by slepage, 19 May 2024 - 06:29 PM.

[MalVeauX]

Hi,

 

Notice its in the center basically, so its interference rings, exacerbated by the double stack and barlow making them quite obvious. The longer the focal-ratio gets, the more obvious the rings will become in general. Often times its the glass plate in front of the sensor of the camera. If the rings are truly fixed in place regardless of orientation a flat calibration frame will at least blend their visibility out a little better as it doesn't seem to be causing major bandpass issues. Otherwise, tilt is the only way to really address it. It depends on the orientation of the tilt and position and how much tilt is needed.

 

Very best,

[HPaleske]

Hi,

 

I can confirm what Marty says. Inclination is the only remedy that helps against Newton rings. I have to tilt the Apollo Max so much that the device on the camera is not sufficient. That's why an extra tilter was placed in front of the camera, which works in addition to the camera tilter. My focal ratio is small, so this measure does not cause any blurring.

 

cs Harald

www.unigraph.de

[slepage]

Thanks both of you,  but tilt was something that I looked at and it had no impact on the bans.  After I reached maximum tilt on the tilter, I took the camera out of the eyepiece holder and via a hand held method, I did every thing from a light tilt to an extreme tilt and the bands remained unchanged.  They did not fade, get fatter, or thinner, or more defused.  They stayed the same.  This is why at first I was thinking it was being generated inside the scope.  Marty, you said that the DS can exacerbate the interference, does that mean that the DS unit might be at fault?  Maybe something not calibrated correctly?

 

However, please note that I did say that when I changed over from the 174mm to the 290mm with the barlow that the bans disappeared. This is making me think that this is totally generated by the glass siting above the sensor. 

Steve

[MalVeauX]

Thanks both of you,  but tilt was something that I looked at and it had no impact on the bans.  After I reached maximum tilt on the tilter, I took the camera out of the eyepiece holder and via a hand held method, I did every thing from a light tilt to an extreme tilt and the bands remained unchanged.  They did not fade, get fatter, or thinner, or more defused.  They stayed the same.  This is why at first I was thinking it was being generated inside the scope.  Marty, you said that the DS can exacerbate the interference, does that mean that the DS unit might be at fault?  Maybe something not calibrated correctly?

 

However, please note that I did say that when I changed over from the 174mm to the 290mm with the barlow that the bans disappeared. This is making me think that this is totally generated by the glass siting above the sensor. 

Steve

No, its not the fault of your double stack. The high contrast and isolation of the CWL along with a long focal-ratio (barlow) will make interference rings pop out in high contrast. A single stack at fast focal-ratio (no barlow) with low contrast and a bright disc will not show them as prominently usually. Again, the origin of the issue is likely just the glass plate in front of your sensor. Not your etalons. You just need a tilt device with more range.

 

Very best,

Edited by MalVeauX, 19 May 2024 - 09:50 PM.

[HPaleske]

...

 

Not all slopes are the same. You also have to consider the angle in which the tilt of the camera has an effect.

 

cs Harald

www.unigraph.de

[slepage]

Why do you think I am having this issue in the 1st place, when my friend who has the exact same scope and his is set up the same way does not?  I had taken my scope down to his place, and we tried inserting his imagining train into my scope and the bans were there, when we put it back in his scope there was no bands? Something with the scope must be different.  Any ideas?

[MalVeauX]

Why do you think I am having this issue in the 1st place, when my friend who has the exact same scope and his is set up the same way does not?  I had taken my scope down to his place, and we tried inserting his imagining train into my scope and the bans were there, when we put it back in his scope there was no bands? Something with the scope must be different.  Any ideas?

Subtle differences in coatings, glass substrate, and assembly. These are not research instruments with years of perfect collimation and alignment with measurements to prove it. They're hand assembled and shipped. None of them are perfectly aligned nor adjusted for internal reflections. So each instrument is subtly unique as none of the elements are orthogonal in reality (merely "close enough") and the ones that are that need tilt do not have optimal tilt for the system. These are mostly checked visually. You could use another camera and notice the interference rings are gone. It's usually the glass in front of the sensor on the camera as the culprit.

 

Very best,

[Skywatchr]

Why do you think I am having this issue in the 1st place, when my friend who has the exact same scope and his is set up the same way does not?  I had taken my scope down to his place, and we tried inserting his imagining train into my scope and the bans were there, when we put it back in his scope there was no bands? Something with the scope must be different.  Any ideas?

Did you try rotating the camera to see if the banding follows the camera or not?  If it does follow, then it would seem the glass covering the sensor is causing it which may be at a tilt itself.

[slepage]

Did you try rotating the camera to see if the banding follows the camera or not?  If it does follow, then it would seem the glass covering the sensor is causing it which may be at a tilt itself.

No, it does not follow.  The bands stay in the same spot.

 

Subtle differences in coatings, glass substrate, and assembly. These are not research instruments with years of perfect collimation and alignment with measurements to prove it. They're hand assembled and shipped. None of them are perfectly aligned nor adjusted for internal reflections. So each instrument is subtly unique as none of the elements are orthogonal in reality (merely "close enough") and the ones that are that need tilt do not have optimal tilt for the system. These are mostly checked visually. You could use another camera and notice the interference rings are gone. It's usually the glass in front of the sensor on the camera as the culprit.

 

Very best,

I can see that.  What worries me about the tilt solution is that I did try tilting up to 3 degrees. Then, I took the camera out and hand tilted it to extreme degrees and the ban looked the same.  Mater of fact, as soon as the camera grabbed light from inside the eyepiece holder I could see the bans and I would approach the eyepiece holder at all different angles.   I just don’t know what to make of it, as it would seem to me that if this could be fixed using tilt, then I should see some difference in the bands as tilt is applied.  No????

[MalVeauX]

No, it does not follow.  The bands stay in the same spot.

 

I can see that.  What worries me about the tilt solution is that I did try tilting up to 3 degrees. Then, I took the camera out and hand tilted it to extreme degrees and the ban looked the same.  Mater of fact, as soon as the camera grabbed light from inside the eyepiece holder I could see the bans and I would approach the eyepiece holder at all different angles.   I just don’t know what to make of it, as it would seem to me that if this could be fixed using tilt, then I should see some difference in the bands as tilt is applied.  No????

There are commonly more than one series of interference rings, very large one, lesser ones, etc. You likely need to tilt in another orientation relative to the sensor. I would orient your tilter so that it's tilting in the plane of the widest dimension of the sensor, align them, and then rotating this so that its relative to gravity so that the imaging train's natural sag to gravity also has tilt in the same plane. Then adjust things.

 

The IMX432 sensor I use has intense interference rings on my F32 double stack. I have to do quite a lot of tilting to deal with it. But, tilting solves it none the less. You just have to keep trying and take a systematic approach with method and keep notes. You'll find a bit of a pattern and it will be less random.

 

Very best,

[slepage]

Thanks Marty for your time on this.  I’ll try your suggestions when I have time this week. Work will stand in the way for the 1st part of the week.

Steve

[HPaleske]

Another tip:
If the Newtonian rings have almost disappeared due to tilting, the best way to combat the rest is to use a flat (brochure cover in front of the lens) in Firecapture. This also makes it easier for the AS3! stacking program and prevents it from getting stuck on structures I regularly make flats, especially when the camera has moved.

 

Good luck and

 

cs Harald

www.unigraph.de

[slepage]

Well, it's now Wednesday, and I should be able to get back out there hopefully this afternoon for testing or tomorrow.  Quick question - Where is the optimal place to put the tilter in your image train?  Closest to the sensor or closest to the blocking filter or it does not really matter?

 

Thanks

Steve

[slepage]

Hi All,  Here is an update.  I decided to order the DayStar Interference Eliminator with T Mount,  this tilter is far easier to use then the 3 point push pull screws on other tilters.  Plus it is easier to tilt more precisely in one plane, since Marty suggested that I tilt along the same plane has the longest edge of the sensor.  here is an image of the tilter attached.  The tape was put in place because if I tighten it all the way the camera was no longer in the correct orientation so I had to untighten it a bit.

 

It was quite easy to dial out the bands, they went away quickly and far from maximum tilt.  The sun image is crap, since this was done in the late afternoon and the seeing was horrible, but the results of getting rid of the bands is all I was after.  So thank you Marty and Harald this is what was needed.  

 

It did seem however to create a new issues:

 

1) My illumination was uneven, with one corner far brighter then the other.  I assume this is from the tilt???  Is there a way to deal with this? 

 

2) and most importantly, when you tilt, do you  need to tweak your tuning of the DS unit?  It seems that the detail is not even across the surface.

 

Your thoughts and suggestions are very welcome.

 

Thanks

Steve

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