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new refractor optics pinched?

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#1 Bdm1010

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Posted 09 November 2019 - 09:06 AM

I just got a new refractor from ts optics its a 90mm triplet.  attached is a zoomed in image of a star in the center of the frame i shot last night. Does this look like pinched optics?  I keep the scope under a telegizmo 365 cover so cooldown isnt an issue.  if it is pinched optics is it as easy as loosening the retaining ring and snugging it back?  i read that the orientation of the glass is very important in triplets so i didnt want to attempt if this was some other issue.  thanks for the help!

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  • pinched.jpg


#2 rachnoman

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Posted 09 November 2019 - 09:33 AM

It's impossible to tell based on your image. Try to use a good quality higher power eyepiece. Then check visually the out of focus star image. 



#3 Dynan

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Posted 09 November 2019 - 09:46 AM

Could be effects of seeing also,. If the pattern remains after different nights and seeing quality, then it might be time to investigate.



#4 Bdm1010

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Posted 09 November 2019 - 10:44 AM

unfortunately i don't have any eyepieces.  im using an asi1600 with focal reducer and filter wheel.

It's impossible to tell based on your image. Try to use a good quality higher power eyepiece. Then check visually the out of focus star image. 



#5 Bdm1010

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Posted 09 November 2019 - 10:44 AM

it has looked like this the various nights i have used it. 

Could be effects of seeing also,. If the pattern remains after different nights and seeing quality, then it might be time to investigate.



#6 imtl

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Posted 09 November 2019 - 10:50 AM

take out the focal reducer and filter wheel. Try just to simply image a star field with a few bright stars in it. Pleiades or something else.

And do proper exposure even clipping the bright stars a bit so we can see clearly what is going on. It could be several things.



#7 Bdm1010

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Posted 09 November 2019 - 11:03 AM

thank you!  looks to be clear tonight so i will make some captures and post the results.

take out the focal reducer and filter wheel. Try just to simply image a star field with a few bright stars in it. Pleiades or something else.

And do proper exposure even clipping the bright stars a bit so we can see clearly what is going on. It could be several things.



#8 Bdm1010

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Posted 09 November 2019 - 10:23 PM

take out the focal reducer and filter wheel. Try just to simply image a star field with a few bright stars in it. Pleiades or something else.

And do proper exposure even clipping the bright stars a bit so we can see clearly what is going on. It could be several things.

this is m45 i did an ABE in pixinsight

 

https://www.astrobin.com/l998dr/



#9 RossW

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Posted 09 November 2019 - 10:29 PM

I don't know about pinched optics but by the look of the elongated corner stars you do not have your backfocus spacing correct and perhaps some image tilt too.



#10 Bdm1010

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Posted 09 November 2019 - 10:33 PM

The linked image is without filter wheel or focal reducer/flatter 

I don't know about pinched optics but by the look of the elongated corner stars you do not have your backfocus spacing correct and perhaps some image tilt too.



#11 sharkmelley

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Posted 10 November 2019 - 04:37 AM

this is m45 i did an ABE in pixinsight

 

https://www.astrobin.com/l998dr/

Your new image makes it a lot clearer what is going on.  Here is one of your stars:

 

StarSpikes.jpg

 

The stars have 3 sets of diffraction spikes with 120 degree rotational symmetry.  Diffraction spikes are caused by something impinging into the light path - in this case three of them 120 degrees apart.  The culprit is likely to be the 3 clips holding the lens cell in place (or are they spacers for the lens elements?) and you can almost certainly see them by looking carefully into the front element of the scope - three little square bits around the circumference.   These clips should not be impinging into the light path, so you need to speak to your supplier about this.

 

Take a look at the simulated stars here:

https://www.cloudyni...tion/?p=6772339

These are caused by the clips holding a Newtonian mirror in place, but the effects are the same and it will help you understand what I'm talking about!

 

Mark


Edited by sharkmelley, 10 November 2019 - 05:35 AM.

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#12 imtl

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Posted 10 November 2019 - 10:32 AM

Your new image makes it a lot clearer what is going on.  Here is one of your stars:

 

attachicon.gif StarSpikes.jpg

 

The stars have 3 sets of diffraction spikes with 120 degree rotational symmetry.  Diffraction spikes are caused by something impinging into the light path - in this case three of them 120 degrees apart.  The culprit is likely to be the 3 clips holding the lens cell in place (or are they spacers for the lens elements?) and you can almost certainly see them by looking carefully into the front element of the scope - three little square bits around the circumference.   These clips should not be impinging into the light path, so you need to speak to your supplier about this.

 

Take a look at the simulated stars here:

https://www.cloudyni...tion/?p=6772339

These are caused by the clips holding a Newtonian mirror in place, but the effects are the same and it will help you understand what I'm talking about!

 

Mark

I agree with Mark. It looks like an obstruction probably near the aperture. Check your lens cell.



#13 Bdm1010

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Posted 10 November 2019 - 11:35 AM

Your new image makes it a lot clearer what is going on.  Here is one of your stars:

 

attachicon.gif StarSpikes.jpg

 

The stars have 3 sets of diffraction spikes with 120 degree rotational symmetry.  Diffraction spikes are caused by something impinging into the light path - in this case three of them 120 degrees apart.  The culprit is likely to be the 3 clips holding the lens cell in place (or are they spacers for the lens elements?) and you can almost certainly see them by looking carefully into the front element of the scope - three little square bits around the circumference.   These clips should not be impinging into the light path, so you need to speak to your supplier about this.

 

Take a look at the simulated stars here:

https://www.cloudyni...tion/?p=6772339

These are caused by the clips holding a Newtonian mirror in place, but the effects are the same and it will help you understand what I'm talking about!

 

Mark

the glass looks to be held in by retaining rings.  i cant see anything protruding into the aperture but the retaining ring has 3 surfaces that touch the glass and a ring on top that tightens this against the glass to hold it in place.  the 3 surfaces dont protrude out into the aperture.  could it be possible that it is to tight and is pinching the glass in these 3 spots making the star look like that?  i have attached a picture of one of the surfaces.  there are 3 and they are in the same orientation as the diffraction spikes.  

Attached Thumbnails

  • ring.jpg


#14 imtl

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Posted 10 November 2019 - 02:30 PM

When holding the scope and looking through, do you see anything in the way like something in the baffles or anything like that?

 

It could also be aperture vignetting since the is a clear feature dominatting the other two 120 and 240 degrees rotated ones. Hard to tell



#15 JukkaP

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Posted 10 November 2019 - 02:41 PM

The collimation screws are too tight for your lens. You can adjust them carefully. I have the same problem with my esprit 80.

Its best to adjust them on normal imaging temperature.

#16 sharkmelley

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Posted 11 November 2019 - 06:28 PM

the glass looks to be held in by retaining rings.  i cant see anything protruding into the aperture but the retaining ring has 3 surfaces that touch the glass and a ring on top that tightens this against the glass to hold it in place.  the 3 surfaces dont protrude out into the aperture.  could it be possible that it is to tight and is pinching the glass in these 3 spots making the star look like that?  i have attached a picture of one of the surfaces.  there are 3 and they are in the same orientation as the diffraction spikes.  

On further research, yes it does seem to be possible that stressing the glass in this manner can lead to diffraction spikes.  Both in this thread and in other threads I have found, owners have found that overtightening of grub screws etc does cause such effects.  The effect I described (something blocking the light path) is certainly one way that diffraction spikes are produced but it seems it is not the only cause.

 

Mark



#17 Monkeybird747

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Posted 11 November 2019 - 07:16 PM

Pinched optics gets my vote as well. Contact TS optics and provide your image. They have pretty good support and can probably guide you on what to do.

#18 tonyt

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Posted 11 November 2019 - 07:39 PM

Any uneven pressure on the lenses can cause similar effects to those observed, whether it's from slightly too tight centering screws, pressure from the retaining ring being too tight or a gap in a broken spacer ring:  http://interferometr...ml?view=sidebar


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#19 sharkmelley

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Posted 12 November 2019 - 01:07 AM

Any uneven pressure on the lenses can cause similar effects to those observed, whether it's from slightly too tight centering screws, pressure from the retaining ring being too tight or a gap in a broken spacer ring:  http://interferometr...ml?view=sidebar

Thanks for that link.  It's good to see a proper laboratory demonstration.

 

Mark



#20 the Elf

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Posted 12 November 2019 - 07:43 AM

 

They have pretty good support and can probably guide you on what to do.

My experience is quite different. Over here they have 4 weeks return only. Make sure you have the right to return it with full money refund even after that period as long as investigations are pending or return it right away if shipping cost is not too high. 

What's your loc?



#21 Bdm1010

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Posted 14 November 2019 - 11:46 AM

i contacted ts optics and they said it was likely the collimating screws that are too tight.  they suggested slightly loosening them.  i asked if i should slightly loosen all the screws which would be 9 screws 3 for each of the 3 lenses, or if i should do just one side of the 3.  i think the language barrier is preventing a definitive answer on this.  what would you guys recommend?  should i loosen the one screw on each of the 3 lenses or loosen all 9?  i feel like if i loosen the 1 it would ease the tension across all three for that lens.



#22 Monkeybird747

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Posted 14 November 2019 - 02:59 PM

Not really sure. I’d either sent them a pic of the screw holes and add circles or question marks to see if that clarifies things. Or, start with the front element and do one lens at a time until the problem disappears. Your probably talking very, very tiny amount of loosening. Maybe you can do it under the stars to see the results live. If there is a way to mark the screw head positions prior to adjustment, it might be worth the effort. FYI, I’ve not done this myself. Good luck!
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#23 tonyt

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Posted 14 November 2019 - 05:10 PM

Releasing pressure on one side of a lens seems risky for collimation - I'd loosen all screws around a particular lens by the smallest amount possible. You won't know which one of the lenses is causing the issue either. It's a shame TS didn't properly check the objective at the shop.




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