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newbie: trouble with Coronado PST

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#76 Live_Steam_Mad

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Posted 07 April 2018 - 08:12 PM

I recently got the chance to compare a local club's PST with my Lunt 50, with the PST being on a photo tripod, side by side with my LS50 on my CG5, at about the same magnifications (Solar disc size) in both scopes, and I studied the surface detail and proms and tuning and sweet spot of both instruments. I studied these all extensively over 2 hours and found that this particular PST has a serious problem with the image brightness (light transmission). 

 

To give you an idea, the first eyepiece I put in was an 8mm which is a decent one to use for Sol in the LS50, but in the PST it was so dim I couldn't work out where focus was and I had to go all the way down to a 32mm Plossl until I could focus the PST properly and precisely. In fact, I found out that my LS50 is still brighter than the PST, at the same sized Sun disc, when the LS50 has a 13 PER CENT TRANSMISSION ND FILTER in the eyepiece!

 

I quickly came to the conclusion that this PST is badly / fully rusted over and the ITF filter needs replacing.

 

It didn't seem to affect the contrast, as it were, (which I thought was odd), since the PST had similar contrast on the surface orange peel texture on the Sun's disc, and the filaments were also similar in contrast compared to the Lunt, just that the visual image was about 1/10 the brightness of my LS50.

 

Regards,

AG.


Edited by Live_Steam_Mad, 07 April 2018 - 08:14 PM.

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#77 drt

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Posted 18 April 2018 - 12:13 PM

Does anyone knows Etalon-Gold pipe thread size?

Thanks in advance.



#78 JS999R

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Posted 18 April 2018 - 11:52 PM

Dave,

I've been tied up at work and I'll respond to this in the next couple days. I've been talking to Christopher Maier and he has shed some new information to consider. The coating on my particular example was too fragile to undergo an acceptable cleaning process I've used a number of times without issue in the past. More later.  

Final update.  After exchanging emails Chris sent me a new filter and it seemed to be just slightly larger in diameter than the first one, I did suggest to Chris that if he made them the same size as the stock Coronado filter there would be no need for an O Ring. I installed the O Ring anyway and now the PST works like a charm, super bright and sharp images too. Chris indicated he didn't have a PST to inspect so I gave him caliper measurements and also sent him the rusty Coronado filter as well.  


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#79 JS999R

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Posted 21 April 2018 - 11:29 PM

Final update.  After exchanging emails Chris sent me a new filter and it seemed to be just slightly larger in diameter than the first one, I did suggest to Chris that if he made them the same size as the stock Coronado filter there would be no need for an O Ring. I installed the O Ring anyway and now the PST works like a charm, super bright and sharp images too. Chris indicated he didn't have a PST to inspect so I gave him caliper measurements and also sent him the rusty Coronado filter as well.  

Chris indicated in an email the O Ring isn't a necessary installation as a precaution to block unwanted light escaping around the ITF filter. As I said, the new ITF filter Chris sent me seemed to be slightly larger than the previous version, but I was so excited to install it I didn't bother measuring the difference. However, I believe now that Chris has the old Coronado filter to use as a model for sizing, in future batches we will likely see him producing filters that will fit snugly in the barrel.

 

I bought my used PST from a nice guy and he even included a Malta tabletop tripod in the deal.  I'm impressed with the build quality of the tripod, all CNC and brass legs.  I looked around and except for a company in the UK, the tripod has been discontinued as an option for the PST.  Man, the retail price was expensive.  My PST didn't come with a factory box so I put the word out for one and got lucky when someone responded they had one, so I bought it.  I got lucky again when I found the box foam insert also had pre-cut lines to accommodate the PST that included the optional Malta tripod.  So I simply pulled the foam elements out which left exact outlines for the Malta tripod head and it's brass legs.  I used the Malta tripod when I tested the new Maier filter and it worked great, but I plan on trying some solar imaging in the future so it looks like my only option, for now, is to mount the PST (with a small Vixen dovetail) to my AP 900GTO.  That should look odd.        


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#80 Live_Steam_Mad

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Posted 25 April 2018 - 10:17 PM

As a follow up to a local club's PST that I posted about in post #76 above, here is a picture that I took tonight of it's ITF filter, after the guy in charge of it got the lower half of the 2 eyepiece side sections off with 2 passes of a desoldering heat gun and a large strap wrench ;-

 

It's fairly easy to see that only the central small area is clear, a very large proportion of the area is clouded over by oxidation. Hence the very dim views, approximately 8 times dimmer than on a club member's own PST at the same magnification. The filter needs replacing. This will be done pretty soon.

 

Regards,

AG

Attached Thumbnails

  • IMG_20180425_203658.jpg

Edited by Live_Steam_Mad, 25 April 2018 - 10:18 PM.


#81 Live_Steam_Mad

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Posted 26 April 2018 - 08:20 PM

Here is a picture of the local club's PST's internal pentaprism. It is an impressive 10 degrees misaligned. This is after it was "repaired" by Meade some years ago ;-

 

PST with a badly misaligned prism produces visual views and photographic images like this ;-

 

http://www.pbase.com...image/148391086

 

The prism will be realigned and a new filter got, soon.

 

Regards,

AG

 

Attached Thumbnails

  • 31351320_10156575517945798_7759103473878040576_o.jpg

Edited by Live_Steam_Mad, 26 April 2018 - 08:21 PM.

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#82 bikerdib

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Posted 27 April 2018 - 07:44 AM

I recently checked my PST, the ITF is still clear but the prisim was badly aligned, similar to the picture above.  I'm trying the "twist back into position" method but so far it doesn't seem to stay completely aligned, better but not 100%.  So, in case I need to re-glue, what is the best adhesive?  I know silicon adhesive works well for glass but it also puts out some bad odors so I'm concerned about out-gassing when the scope is reassembled.



#83 DAVIDG

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Posted 27 April 2018 - 08:17 AM

 The silicon adhesive used to seal aquariums are not acid catalyzed so will have  low  out gassing and it won't be acetic acid.   I have aligned around 12 PST and what I have found is that  you need to slowly twist the prism so it passed the position of were it would be aligned and then let it relax back into place. It may take a few tries.  I aligned the prisms in my three PST almost 10 years ago and they are still perfectly aligned.

 

                       - Dave   


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#84 bikerdib

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Posted 27 April 2018 - 07:33 PM

Thanks Dave.  I have done that (twist past then let relax).  It is better but not yet where it should be.  I may twist it past then use some lens cleaning tissue to block it in that position for a few days and see what happens.



#85 DAVIDG

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Posted 29 April 2018 - 11:30 AM

Thanks Dave.  I have done that (twist past then let relax).  It is better but not yet where it should be.  I may twist it past then use some lens cleaning tissue to block it in that position for a few days and see what happens.

  Yes that what I done also  but added a layer of cardboard between the body of the PST and the lens tissue to  make it thicker. That way I could use the focuser to move the prism fully forward and hold it place against the inner surfaces of the PST body. 

 

               - Dave 


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#86 Astro Canuck

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Posted 04 April 2019 - 08:51 AM

2019 - used PST:  Noted the small screw in the tuner is stripped and does not tighten, Had the plate off and all the optics are clean and no rust any were.

I looked at the sun again.. and the tuner does make things appear to come and  go, but there was a slight dark thin area that moved over the disk as I tuned but did not effect the image or make the sun double.

 

 It is when I tune the filter I can see a slight movement of a bottom lens (?) when looking down the tube.. shifts a bit but not much.

 

Thanks

 

Mike



#87 DAVIDG

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Posted 04 April 2019 - 10:10 AM

 Posting a picture of the ITF filter at the bottom the focusing tube would be great to be sure it is not rusted. Many times they are so rusted they look uniform. The ITF is filter that you see when you take the side cover off and it is at the very bottom of the eyepiece tube, not the filter that when remove the eyepiece and look down

   The "lens" you are seeing moving when you turn the tuning ring is actually the Etalon being tilted to bring it on band and that is what you should see.  

   It is easy to strip  out the small screw that passes through the tuning ring and into the tuning mechanism but once in the correct position a bit of super glue will hold it in place.  There are a number of holes in the tuning mechanism that is under the  tuning ring  that the screw can fit into that allow a different amount of movement. That causes a different amount of  tilt to the Etalon. It is possible that the former owner took the screw out and then put it back in so it is the wrong position. So now the  tuning ring is not moving the Etalon into the  range to bring it on band so you can see H-alpha detail on the Sun. 

   Before adjusting the position of the screw into a different hole, I would look at an internet site like GONG http://halpha.nso.edu/

to see a real time images of the Sun in H-alpha to be sure there is activity to view, then see if you can tune your PST to see it. 

 

          - Dave 



#88 Bagwell

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Posted 09 June 2019 - 12:53 AM

Great thread, thanks for all the help and suggestions etc.   I had an out of alignment prism and I still need to remove the eyepiece holder to see if the ITF is ok.  

 

Thanks, 
Vaughn



#89 bdaniele79

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Posted 23 July 2019 - 07:30 AM

This thread is awesome!!

used PST made in Mexico found on Ebay and arrived last week, first test was disappointing compared to my old PST made in USA, image dark image and no prominence. So i done some internet search and find this thread full of suggestion.

Now the PST is disassembled and cleaned , prism is aligned (twist past then let relax) and I think that ITF is rust.

can someone confirm it's rust?

ITF.jpg ITF2.jpg

 

and now? how to remove the filter from the eyepiece holder?

this tool is good? https://www.amazon.i...0?ie=UTF8&psc=1

 

thank you very much too all those who have contributed to this thread!



#90 DAVIDG

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Posted 23 July 2019 - 08:47 AM

 Yes  your ITF filter is totally rusted over and the tool in your link with work to easily unscrew the retainer ring to replace the bad ITF with a new one.

 

            - Dave 



#91 bdaniele79

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Posted 01 August 2019 - 11:34 AM

Just arrived the new Maier ITF filter, the red side facing eyepieces? and the green side to incoming light?

Another question: there was a little of glue that stopped the ring to block the ITF, is it better to put some glue again? and what kind of glue?

Thank you!


Edited by bdaniele79, 01 August 2019 - 11:34 AM.


#92 Andre444

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Posted 07 November 2019 - 03:34 PM

Hi, I wonder why my 3 year pst still dond show any sign of rust, while it is exactly the same ITF as any other pst? And what are the differences between a not rusted Maier filter, beloptic and original Made filter for visual in terms of contrast and brightness? ( although my made filter is not rusted I can't use a 2x Barlow lens and 12 mm Eyepiece, even not in decent conditions. I use  20 and 15 mm in average conditions. And if the seeing get decent ( good seeings are pritty rare in west Europe sometimes even decent are rare). I use the seben zoom and put it on up to12 mm setting and verry decent conditions 10- 8 mm for the proms.  Thanks.


Edited by Andre444, 07 November 2019 - 04:09 PM.


#93 JoseBorrero

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Posted 07 November 2019 - 03:37 PM

Hi, I wonder why my 3 year pst still dond show any sign of rust, while it is exactly the same ITF as any other pst? And what are the differences between a not rusted Maier filter, beloptic and original Made filter for visual? ( although my made filter is not rusted I can't use a 2x Barlow lens and 12 mm Eyepiece, even not in decent conditions. I use 20 and 15 mm in average conditions. And if the seeing get decent ( good seeings is rare in west Europe) I use the seben zoom and put it on the 12 mm setting and verry decent conditions 10- 8 mm. Thanks.

Usage?

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#94 tjrudyk

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Posted 04 May 2022 - 09:55 AM

Hey all,

 

  I realize this is an old thread, but I need some advice. I work over at the Dunn Solar Tower in Sunspot (ha!) NM.  I've got a Coronado that seems to have a little problem...photo included.  There is a dust cover clip and spring INSIDE the optical tube. This had to have come from the factory this way. I'm figuring it will be easier to get the front gold tube off that to have to dig through piles of paper work and red tape to figure out who/when it was bought.  I saw the post where the tube had been removed using some masking tape among other implements of destruction, was wondering if anyone had some more advice on getting that gold tube off.

IMG 20220504 081249854 HDR[1]


#95 tjrudyk

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Posted 04 May 2022 - 09:59 AM

Update: I got in through the front objective cell. It was easy to get off. Duh.


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