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#51 Jairo

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Posted 13 January 2020 - 10:02 PM

 It is a pretty simple repair. You need to unscrew the top section of the eyepiece barrel from the main body of the PST.  Once that is off you need to unscrew the retainer ring that holds the ITF filter in place. Usually the retainer ring has two slots in it that either a lens spanner wrench is used to loosen it or just a thin strip of metal that spans both slots. With the ring removed the old filter just drops out and you drop in the new one. Replace the retainer ring and just snug it up. don't over tighten it since you want the filter to be able to expand from any heat. Screw the eyepiece barrel back in place and enjoy the much improved views.

 Here is  a link to one of the many threads here that show the process https://www.cloudyni...nado-pst/page-3

 

                  - Dave 

Thank you. I could do it and I saw my first proeminences in three years.

But I noticed some slight Newton rings at f/10 for the first time too. Could it be because the new filter axis is slightly misaligned?



#52 DAVIDG

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Posted 14 January 2020 - 09:35 AM

 Did you see the Newton's ring visually or photographically ? I have never seen them visually. The mounting surface for the ITF seems to be machined at a slight angle so you can rotate the ITF and that may change the angle enough so the rings are not visible.

 

                      - Dave  



#53 Jairo

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Posted 16 January 2020 - 09:30 AM

 Did you see the Newton's ring visually or photographically ? I have never seen them visually. The mounting surface for the ITF seems to be machined at a slight angle so you can rotate the ITF and that may change the angle enough so the rings are not visible.

 

                      - Dave  

I saw them in video from my ASI120MC, and they were still there after stacking some 700 of such frames.



#54 DAVIDG

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Posted 16 January 2020 - 10:24 AM

I saw them in video from my ASI120MC, and they were still there after stacking some 700 of such frames.

 It is not a  problem with the  ITF filter but the interaction  of monochrome light between the glass cover over the CCD and the front surface of the CCD itself.  You have the same conditions that one sets up when testing surfaces for optical flatness by place  two surface very close together to cause the the interference fringe to form under monochrome light.  It is common problem with many CCD cameras when used with very narrow band monochrome light. 

 

                       - Dave 



#55 Jairo

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Posted 17 January 2020 - 12:30 PM

 It is not a  problem with the  ITF filter but the interaction  of monochrome light between the glass cover over the CCD and the front surface of the CCD itself.  You have the same conditions that one sets up when testing surfaces for optical flatness by place  two surface very close together to cause the the interference fringe to form under monochrome light.  It is common problem with many CCD cameras when used with very narrow band monochrome light. 

 

                       - Dave 

Any idea of why it didn't appear before?



#56 SgrB2

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Posted 17 January 2020 - 01:07 PM

It's not the exact same optical system.  Invest in a zwo tilt adapter ($38)

to rid the rings.


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#57 bignerdguy

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Posted 18 January 2020 - 05:02 PM

I saw this post and decided to look at my PST to see if it suffered from the same issues.  I had always thought it worked fine until i saw this post. Once i disassembled it i found two issues.  first was it was most definitely NOT aligned however the mounts are not loose, they are glued tightly to the prism but it was still not perfectly aligned.  The second was Rust on the filter as described here.  See attached photos.  The mount was slightly off center on both sides and looks to have been that way from the factory.  Wonder if that is actually by design? however from the discussions here i am also wondering if it wasn't simply a manufacturing flaw.  Either way i will need to replace the filter and fix, somehow, the prism without damaging it. 

 

Any ideas on how to remove the mount pieces without fracturing or damaging the prism?

Attached Thumbnails

  • filter.jpg
  • Prizm-2.jpg


#58 jgraham

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Posted 20 January 2020 - 09:06 AM

If you were happy with the image quality I'd be tempted to leave the prism as-is. The ITF is another issue. I'm looking at replacing mine as I'm sure that it needs it. I haven't taken mine apart yet, but I noted how dim the sun has been looking through my PST lately. I had the original rust problem fixed several years ago, so it should be that.

 

One crisis at a time...



#59 Bagwell

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Posted 20 January 2020 - 09:16 AM

There are a couple of threads on this repair and suggestions on this site. The one I followed was to replace the filter with a new one and to use my fingers and a lense type of cleaning rag (as to not put finger prints on the prism) to force the prism back in to alignment holding it for a number of seconds or maybe even a minute to allow the rtv or whatever type of glue is holding it to adjust to the new alignment.  It does work that way.  You might even put the prism assembly in a warmish place to allow things to come up to a warmer temp first before trying to realign it.  I had to over rotate the prism in its glued in state and hold it over rotated so that when releasing it it would settle in at the proper alignment.  It takes a few tries and patience.  No one that I know of has taken the prism assembly apart from the rtv or glue or foam to realign it unless it was broken away from that stuff already and not really being held in properly in the first place.  Good luck and keep an eye out for the other PST repair threads explaining this further.  


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#60 DAVIDG

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Posted 20 January 2020 - 10:23 AM

 The prism when misaligned causes astigmatism in the image which soften the view. It is an optical fact that  the scope wasn't designed to have the prism out of alignment. The problem is that what ever type of adhesive Meade is/was using allows the prism to sag out of alignment until it is fully cured. That seems to be much longer then the time that was allowed from them the adhesive to be set before the scope fully assembled so they drift out of alignment with time.

    On the  12 or so that I have repaired including two of my own, I slowly applied twisting pressure to the prism to move it back into alignment. Usually you have to go past the correct position and let it relax into place. Once it is aligned the ones I have worked on have stayed that way. It has been at least 5 years since I did my two and when checked they are still aligned.  The adhesive that I have seen on the ones I have repaired has been black and gooey to the touch.  Yours looks to clear RTV.  Is it soft or hard too the touch ? 

   Replacing that totally rusted over ITF with a clear one will make a easily visible difference in the brightness and sharpness of the image. 

 

                    - Dave 


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#61 wrnchhead

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Posted 20 January 2020 - 01:15 PM

Using DavidG’s instructions from other threads, I realigned my prism quite easily and replaced the ITF with one from Maier. Noticeable improvement. My filter was not as bad as some I have seen but it was probably at least 50% rusted over.
https://www.amazon.com/dp/B00QRPWCN0
This lens wrench worked great @$20
This also may useful to someone, The smaller of these strap wrenches took my eyepiece holder section apart easily.
https://www.lowes.co...ol-Set/50029434

Edited by wrnchhead, 20 January 2020 - 01:19 PM.

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#62 Jairo

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Posted 20 January 2020 - 01:45 PM

It's not the exact same optical system.  Invest in a zwo tilt adapter ($38)

to rid the rings.

Sorry, but what is a tilt adapter, and what is it supposed to do?



#63 SgrB2

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Posted 20 January 2020 - 10:03 PM

The black anodized metal ZWO T2 Tilter is used to adjust your camera's imaging plane. When doing solar imaging, the T2 Tilter can help reduce Newton's rings interference pattern.  Do a

google search on "zwo tilt adapter" and you'll see them advertised.



#64 44ye

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Posted 21 January 2020 - 11:37 AM

Jairo

 I dont remember the post reference on the ITF but someone found when they rotated their new ITF it removed the rings and artifacts . The post was several years ago . Hope it works / helps you .

Don



#65 bignerdguy

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Posted 22 January 2020 - 04:00 PM

There are a couple of threads on this repair and suggestions on this site. The one I followed was to replace the filter with a new one and to use my fingers and a lense type of cleaning rag (as to not put finger prints on the prism) to force the prism back in to alignment holding it for a number of seconds or maybe even a minute to allow the rtv or whatever type of glue is holding it to adjust to the new alignment. It does work that way. You might even put the prism assembly in a warmish place to allow things to come up to a warmer temp first before trying to realign it. I had to over rotate the prism in its glued in state and hold it over rotated so that when releasing it it would settle in at the proper alignment. It takes a few tries and patience. No one that I know of has taken the prism assembly apart from the rtv or glue or foam to realign it unless it was broken away from that stuff already and not really being held in properly in the first place. Good luck and keep an eye out for the other PST repair threads explaining this further.


I managed to do as you suggested with the prism. You were right its a gummy type of glue and nit a solid one so the mount twisted easily. If i wanted to actually remove it, it might be possible to twist it off. However there wasn't any need to do so, the prism is now on straight. Thank you for the help. Now to save up for the filter...
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#66 bignerdguy

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Posted 22 January 2020 - 05:22 PM

As others have found out the filter barrel is on really tight! i had to use a lock wrench to get it off.  Once off, i was able to remove the secondary filter, that was rusted, with ease.  Here is a photo of what it looks like edge on. You can see it appears to be made of two or three elements and is not sealed.  If you look closely the element facing up is what is rusted.  The rust also does not extend all the way to the edge of the glass since the coating is also not all the way to the edge.  only the metal coating is rusted, the rest of the filter elements are normal.

Attached Thumbnails

  • filter 2.jpg

Edited by bignerdguy, 22 January 2020 - 05:23 PM.



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