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Debugging suggestions pls... fix so far is partial

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#1 sbharrat

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Posted 05 April 2021 - 08:46 AM

So I have been grinding through the non-fun part of this hobby: when things don't go right AND you have already gone through the obvious/easy fixes frown.gif. After 3 months of waiting, I received my TS PL80 apo last week (FPL53 triplet). Nice scope, nice mechanicals. But then there was the dreaded first light with "what's wrong with my stars" 

as-received.jpg

 

(in case not obvious, this is a stack of the bright star in middle of Leo triplet)

 

I have posted about this initially and got some useful suggestions from Dan (DRK) and Dave (Cotts) which I have done. And Mike (in Rancho) pointed to me a website with some really good description. I also got a response to my query from APM telescopes. Between all of these, I backed off the centering screws around the lens cell. There are 4 sets of 3 each, and I backed off 1/8 turn. This did make an major improvement. 

after-fix1.jpg

 

To my eyes at least (and at this point, I totally understand I could be imagining things), there is a still something wrong in "top" part of the star. I tried for a long time last night to figure which of the 4 sets of screws needed further adjustment using the method suggested by Dave (putting a bright star out of focus and trying to see the silhouette) without success. 

 

So, any additional suggestions on how I figure out where this might be coming from? Appreciate your thoughts. Please let me know what other data might be useful to help.

 

PS: in a refractor, the image on the sensor is upside down so if I were to be able to see a silhoutte towards the "top" of the image, it is actually towards the bottom of the scope objective? Or does the flattener in the path change this? 

 

 

 



#2 sbharrat

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Posted 05 April 2021 - 08:54 AM

Added thumbnails of calibrated images of individual subs...

 

Before any fixes:

as-received-single-sub.jpg

 

After centering screws backed off:

after-fix1-single-sub.jpg

 

PS: a gentle nudge that I am starting to be unrealistic in what I should be expecting also useful laugh.gif



#3 Tapio

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Posted 05 April 2021 - 09:06 AM

That last one doesn't look too bad.
Always worries when you start pixel peeping 😁
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#4 klaussius

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Posted 05 April 2021 - 09:10 AM

This looks like retention clips intruding into the optical path. Usual fix is to add a circular mask to prevent that diffraction pattern.

Edited by klaussius, 05 April 2021 - 09:27 AM.


#5 sbharrat

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Posted 05 April 2021 - 09:14 AM

This looks like retention clips intruding into the optical path. Usual fix is to add a circular mask to prwvent that diffraction oattern.

Yes, I read about this too.

 

Dumb question: what *exactly* is this circular mask? Do I just cut a circle just less than 80mm and attach in front of the lens cell? If you have any links to threads that discussed this, would appreciate it. 



#6 klaussius

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Posted 05 April 2021 - 09:32 AM

Yes, I read about this too.

Dumb question: what *exactly* is this circular mask? Do I just cut a circle just less than 80mm and attach in front of the lens cell? If you have any links to threads that discussed this, would appreciate it.


I have no links at hand, but yes, it's pretty much that. You can build a quick mask with cardboard. It needs to be perfectly circular and cover the clips, so if you can visually spot them it would be ideal.

#7 Mike in Rancho

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Posted 05 April 2021 - 03:29 PM

Well, two steps forward anyway...

 

Your subs and even the stacks seem a little rough.  Maybe try to fully process a stack to see what you are fully dealing with here.  Full processing should clarify the defects, and frankly that's what you will be doing anyway so you'll want to know what your bright star halos look like as an end result.

 

I can still see the three major defects even in the new stack.  One clearly, the second less so, the third just barely a hint of it.  But they're there.  I don't know if you have maxed out screw loosening adjustment without losing lens alignment.  But that'll have to be between you and TS, as well as whether this is a return or repair.  Do they have US based service?

 

Does your shield cap have a removable center cap?  That's a good, but often rather small, way to check if this is an issue with the very outer aperture circumference.  DIY masking as well, as was noted.  Cardboard is kind of hard to get right, for me anyway.  I've used a plastic lid that fits my dew shield with a hole cut in it, or things like construction paper or manila folder, for my testing.  Perfect circles are hard to make, but you can end up with some very pretty sharp diffraction spikes kind of like a stopped down camera lens.

 

Other things you might try are an artificial star (you can make one with a flashlight), though if tested inside you might need a lot of extra backfocus, or a reverse flashlight test to shine your aperture opening onto a screen or wall.  That's posted around here in a few places, but basically the flashlight is a foot or more away and you shine through an EP with focus at infinity.

 

You can also examine the lens closely for any outer aperture defects.  I don't know how this TS is built.  You said you found a video of a teardown?  Assuming it is a good analogue to your telescope, I'm curious how TS holds in the lenses and sets the final aperture.  So, you might see an o-ring, which could have a gap, or there might be a separator ring with little foot pads, possibly sticking out slightly.

 

Finally, another way you might be able to make an aperture mask, but with perfect circularity and edges, is to fit a split o-ring on top of your outer lens surface.  Similar to how I modded my scope (100ED thread in Refractor forum), but not made permanent as I did since you will not want to be unscrewing your outer retaining ring on a triplet.  This would depend if you have the space and curvature for a rubber ring to stay put, of course.  For sizing it would be trial and error.  You want just barely enough masking to mask out the defects and set a new aperture, but no more since you want to be sacrificing as little aperture as possible.  But anyway, try cardboard or construction paper first to see if it even does what you want it to in cleaning up the star halos.


Edited by Mike in Rancho, 05 April 2021 - 03:30 PM.

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#8 sbharrat

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Posted 05 April 2021 - 04:39 PM

Inline...

 

Well, two steps forward anyway...

 

Your subs and even the stacks seem a little rough.  Maybe try to fully process a stack to see what you are fully dealing with here.  Full processing should clarify the defects, and frankly that's what you will be doing anyway so you'll want to know what your bright star halos look like as an end result.

 

SJB> These are just a few subs stacked. Haven't gotten much with all the debugging.

 

I can still see the three major defects even in the new stack.  One clearly, the second less so, the third just barely a hint of it.  But they're there.  I don't know if you have maxed out screw loosening adjustment without losing lens alignment.  But that'll have to be between you and TS, as well as whether this is a return or repair.  Do they have US based service?

 

SJB> Haven't gotten there yet.

 

Does your shield cap have a removable center cap?  That's a good, but often rather small, way to check if this is an issue with the very outer aperture circumference.  DIY masking as well, as was noted.  Cardboard is kind of hard to get right, for me anyway.  I've used a plastic lid that fits my dew shield with a hole cut in it, or things like construction paper or manila folder, for my testing.  Perfect circles are hard to make, but you can end up with some very pretty sharp diffraction spikes kind of like a stopped down camera lens.

 

SJB> No, solid shield cap. 

 

Other things you might try are an artificial star (you can make one with a flashlight), though if tested inside you might need a lot of extra backfocus, or a reverse flashlight test to shine your aperture opening onto a screen or wall.  That's posted around here in a few places, but basically the flashlight is a foot or more away and you shine through an EP with focus at infinity.

 

You can also examine the lens closely for any outer aperture defects.  I don't know how this TS is built.  You said you found a video of a teardown?  Assuming it is a good analogue to your telescope, I'm curious how TS holds in the lenses and sets the final aperture.  So, you might see an o-ring, which could have a gap, or there might be a separator ring with little foot pads, possibly sticking out slightly.

 

SJB> The triplet is in a lens cell which screws off. Then the lens are all held in by a retaining ring and centered with 4 sets of screws around the outside. (See pictures below). I don't see anything jutting out. The only thing non-smooth is two indents in the retaining ring: looks like where a tool that they use to screw it in holds. But these are 180 degree apart so wouldn't seem that these could cause the pattern. 

 

Finally, another way you might be able to make an aperture mask, but with perfect circularity and edges, is to fit a split o-ring on top of your outer lens surface.  Similar to how I modded my scope (100ED thread in Refractor forum), but not made permanent as I did since you will not want to be unscrewing your outer retaining ring on a triplet.  This would depend if you have the space and curvature for a rubber ring to stay put, of course.  For sizing it would be trial and error.  You want just barely enough masking to mask out the defects and set a new aperture, but no more since you want to be sacrificing as little aperture as possible.  But anyway, try cardboard or construction paper first to see if it even does what you want it to in cleaning up the star halos.

 

SJB> Still hoping to fix without stopping down. Might eventually get here but hoping to make some progress without.

IMG_6353.jpg

IMG_6354.jpg

IMG_6355.jpg

 


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#9 Mike in Rancho

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Posted 06 April 2021 - 04:25 AM

Understandable, and I thought the same thing at first.  That's my 100mm, and I want it now! lol.gif  Fortunately my ultimate solution left me at 99.7mm, so the sacrifice was worth it.

 

4 sets of 3 screws instead of 6, interesting.  And yeah those indents would be for a spanner wrench.  My outer ring had little holes, but the spanner I ordered had inserts for either.

 

Seems you are on the right track as far as too-tight centering screws, and since the remaining defects look to be in the same spots, that's maybe still it.

 

I honestly don't know the physical mechanism by which those screws being too tight results in the bad halos, so I'm not sure if an aperture mask test will help to uncover the source.  Maybe?

 

It's hard to tell what's below your retaining ring too.  It looks like a second, thinner ring, and then...dunno.  And is that already a rubber o-ring below that, right above the outer lens?  If so, then if it is smooth with no gaps, I would assume your aperture circumference is okay and the only remaining cause is pinching from tightness.  Though your defects still look like they are 120 degrees apart, not 90 that I would think from the 4 sets of screws.


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#10 sbharrat

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Posted 06 April 2021 - 06:03 AM

...  Though your defects still look like they are 120 degrees apart, not 90 that I would think from the 4 sets of screws.

Hmmm. The field flattener is held in focuser tube by 3 compression screws. Next thing to look at. 

 

I really appreciate your thoughts and musings on this Mike. 

 

Cheers!


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#11 Mike in Rancho

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Posted 06 April 2021 - 04:20 PM

Hmmm. The field flattener is held in focuser tube by 3 compression screws. Next thing to look at. 

 

I really appreciate your thoughts and musings on this Mike. 

 

Cheers!

Like a nose piece?  I can't quite see how that might impact things, but...?

 

Anyway, like a dummy I totally forgot a pretty good way to rule out the location of defect sources:  rotate things.  Like 1/4 turn, and see what the funny star halo shapes follow, or don't follow.  So yeah when I was doing this, I rotated the camera orientation and even the lens cell, since that threads on.  Since my FR is threaded to the T-ring there wasn't much I could do there except try without an FR.  But, my halo problems followed the lens cell when I rotated that, pointing me to at least the general end of the telescope where the problems were.  And also ruling out my internal baffles.


Edited by Mike in Rancho, 06 April 2021 - 04:21 PM.

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#12 sbharrat

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Posted 06 April 2021 - 09:38 PM

Update:

 

Yesterday I went through a second sequence of loosening the center screws on the lens cell. (APM telescopes said that all 12 screws visible on the outside were centering screws and not collimation screws.) This time, I might have done more than 1/8 in my frustration so in total between 1/4 to 3/8 off from where I received it. 

 

This is the bright star in middle in Leo triplet. First light for scope:

as-received-single-sub.jpg

 

After first "fix" of backing out lens cell screws by 1/8

after-fix1-single-sub.jpg

 

After second "fix" of backing out lens cell screws by additional 1/8 - 1/4. 

fix2-star.jpg

 

 

Looks good right? smile.gif

 

 


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#13 Mike in Rancho

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Posted 07 April 2021 - 01:45 AM

Significantly more round!  Even zoomed in more.  I say it's time to stack a whole bunch up, calibrate, process, and see how those stars look as a final product.  Well done.


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#14 RedLionNJ

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Posted 07 April 2021 - 06:27 AM

Significantly more round!  Even zoomed in more.  I say it's time to stack a whole bunch up, calibrate, process, and see how those stars look as a final product.  Well done.

Totally agreed.  As part of additional testing, see how great a focus you can achieve (smallest FWHD). A critical focus where the star covers a handful of pixels will make any residual issues really jump out. Check each corner, too - not just the middle of the field.

 

I always love successful troubleshooting stories!


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#15 sbharrat

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Posted 08 April 2021 - 08:49 AM

Update:

 

All is not well frown.gif As part of debugging per APM telescopes instructions, I ran into something else. Basically, when I look at out of focus bright star through an eyepiece, a small portion of the star is "cut off".

 

My hand drawing of this show below. Note that the lines ARE circles, not astigmatic. But a portion of the star is "missing" (this is with the star in the middle of the FOV). Nothing in the optical path was obvious.

star-draw.jpg

 

You can *almost* see this on a 1 sec exposure blown up....

star-pic.jpg

 

Anyway, I have no idea at this point and will be sending the scope back to Germany for evaluation/fix (shipping turns out waaaay more expensive than I would have imagined). frown.gif



#16 Jared

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Posted 08 April 2021 - 09:12 AM

I suspect one of the elements has become de centered from the other two as a result of the loosening of screws. I know you had to loosen, so not criticizing. It seems likely that only one of the three elements actually needed the loosening, and the other two were fine before.

If you haven’t yet shipped it off, you could try one more thing (to avoid the cost and delay of sending it back, not because it’s actually your responsibility)... Assuming you were careful when you backed the screws out evenly, you could try re-tightening them evenly, all except one set of four (either top, middle, or bottom). If you noticed when unscrewing them before that one set seemed tighter than the rest, that’s the set I would NOT re-tighten. Just do the other eight screws.

It’s a “Hail Mary” that probably won’t work, but might be worth it considering the long delay and expense you will otherwise be experiencing.
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#17 jonnybravo0311

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Posted 08 April 2021 - 09:34 AM

What is this "eyepiece" thing of which you speak?

 

Given this strange, new aberration to the star shapes you're seeing in the eyepiece, how do things stack up? Your single sub _may_ show _something_ ... but you've zoomed WAAAAY in to blow that star up so we can see the individual pixels. How does an image look when you _aren't_ pixel-peeping? Are the stars so obviously misshaped that the image becomes completely unusable?

 

Don't get me wrong, I believe you should have a perfectly functioning scope - you DID purchase a scope with an expectation that it actually behaves as advertised. However, given the absurd cost in shipping the scope back to Germany and the subsequently absurd wait for them to evaluate it, and then another potentially absurd time for them to either fix it, or acquire a new one from the manufacturer... to use a phrase one of my coworkers likes, "Is the juice worth the squeeze?"


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#18 sbharrat

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Posted 08 April 2021 - 10:17 AM

What is this "eyepiece" thing of which you speak?

 

Given this strange, new aberration to the star shapes you're seeing in the eyepiece, how do things stack up? Your single sub _may_ show _something_ ... but you've zoomed WAAAAY in to blow that star up so we can see the individual pixels. How does an image look when you _aren't_ pixel-peeping? Are the stars so obviously misshaped that the image becomes completely unusable?

 

Don't get me wrong, I believe you should have a perfectly functioning scope - you DID purchase a scope with an expectation that it actually behaves as advertised. However, given the absurd cost in shipping the scope back to Germany and the subsequently absurd wait for them to evaluate it, and then another potentially absurd time for them to either fix it, or acquire a new one from the manufacturer... to use a phrase one of my coworkers likes, "Is the juice worth the squeeze?"

Borderline. If I had been using this scope and it "developed" this along the way, would not worry about getting it fixed. But I just got it, haven't fully incorporated into my setup, so it doesn't feel as much of a big deal to not have it for an additional month or two. If I don't get it fixed now, I never will and with my mentality, I will occasionally rue that decision in the years to come. 

 

In terms of a total do over, I probably would get the GT81 instead. About $600 more total (including flattener) but significantly fewer reported instances of problems off the bat compared to this clone set of scopes now that I look more carefully. 

 

Live and learn waytogo.gif


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#19 Mike in Rancho

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Posted 08 April 2021 - 01:02 PM

Darn. Unfortunately I was kind of expecting this.  I didn't mention it because, for one, I was waiting for a fully processed test image to clarify your star shape, and two, I actually had a small break in the skies and managed to get an hour and half on Markarian's Chain late last night.  Sorry!

 

But, yeah I saw that flat spot.  And if you look closely, it's in your "before" pictures as well.  Sort of hidden by the halo flare and the three indentations, but it's there.  I think it's usually that bottom right corner that is flattened, though there are at least a couple threads on this.

 

I would do the same thing now on the return, and I don't see that any collimation/centering screw loosening caused it.  That could possibly result in some other errors, but I'm not so sure about squaring a star off.  As a last resort you could maybe try an artificial star to rule out mount movement, but again I'm having a hard time trying to figure how that would cause a flat spot.

 

As for a WO replacement, well you may have noticed the star halo and centering screw thread that just came back to the first page today...

 

Imaging sure does push these things to their limits and exposes flaws, doesn't it?

 

EDIT:  nevermind on the static artificial star test.  I just realized you said you did a defocus test on a live view. 


Edited by Mike in Rancho, 08 April 2021 - 01:24 PM.

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#20 sbharrat

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Posted 08 April 2021 - 03:20 PM

Darn. Unfortunately I was kind of expecting this.  I didn't mention it because, for one, I was waiting for a fully processed test image to clarify your star shape, and two, I actually had a small break in the skies and managed to get an hour and half on Markarian's Chain late last night.  Sorry!

 

But, yeah I saw that flat spot.  And if you look closely, it's in your "before" pictures as well.  Sort of hidden by the halo flare and the three indentations, but it's there.  I think it's usually that bottom right corner that is flattened, though there are at least a couple threads on this.

 

I would do the same thing now on the return, and I don't see that any collimation/centering screw loosening caused it.  That could possibly result in some other errors, but I'm not so sure about squaring a star off.  As a last resort you could maybe try an artificial star to rule out mount movement, but again I'm having a hard time trying to figure how that would cause a flat spot.

 

As for a WO replacement, well you may have noticed the star halo and centering screw thread that just came back to the first page today...

 

Imaging sure does push these things to their limits and exposes flaws, doesn't it?

 

EDIT:  nevermind on the static artificial star test.  I just realized you said you did a defocus test on a live view. 

Really appreciate your thoughts and suggestions on this Mike. It really helped to have the extra perspective. 

 

Back to my "bad but works" achro scope for now.... 




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