Dismantling and modification of a PST CaK

Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...
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Dismantling and modification of a PST CaK

Post by bart1805 » Sat Oct 13, 2018 11:54 am

Here is the story of dismantling a PST CaK. In the end, the plan is to start spring with a doublestacked CaK filter.

1. The original PST CaK

Image20181012_183558_resized_1 by bart moors, on Flickr

2. Problem number 1, destroyed one of the screws, so had to drill it out.

Image20181012_184327_resized_1 by bart moors, on Flickr

3. The inside of the PsT CaK

Image20181013_113749_resized_1 by bart moors, on Flickr

It looks exactly the same as a "normal" PST

Image20181013_113909_resized_1 by bart moors, on Flickr

Two other pictures of the inside of the PST, first one from the front, seconde one from the top (right side points to the frontlens).

Image20181013_121223_resized_1 by bart moors, on Flickr

Image20181013_121239_resized_1 by bart moors, on Flickr

Here you can see the retaining ring that holds the cell the #2 filter is placed in.

Image20181013_113827_resized_1 by bart moors, on Flickr

4. The #2 filter
It is quite easy to release the filter cell, just by turning the retaining ring. Use a screwdriver (gently) and it pops out.

Image20181013_114905_resized_1 by bart moors, on Flickr

Yes it is damaged.

Image20181013_115114_resized_1 by bart moors, on Flickr

And consists of two pieces.

Image20181013_115039_resized_1 by bart moors, on Flickr

5. The front lens
With a lens spanner it is east to pop the front lens out.

Image20181013_114121_resized_1 by bart moors, on Flickr

And here it is, lying on the retainer ring.

Image20181013_115630_resized_1 by bart moors, on Flickr

6. You can see the #1 filter and the retaining ring.

Image20181013_115716_resized_1 by bart moors, on Flickr

Could reach the retaining ring, but could not move it. So that is it for now, winter is still long. Will try again to remove the tube the way it is supposed. But otherwise will drill two holes in it and use a metal rod to twist everything.

If anybody needs other pictures, please let me know, it is all lying around here.

CS! Bart.

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Re: Dismantling and modification of a PST CaK

Post by christian viladrich » Sat Oct 13, 2018 12:15 pm

Thanks a lot Bart !!
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Re: Dismantling and modification of a PST CaK

Post by christian viladrich » Sat Oct 13, 2018 12:21 pm

Just wondering whether you could apply some heat arround filter n1 ? Maybe there is some glue ?
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Re: Dismantling and modification of a PST CaK

Post by bart1805 » Sat Oct 13, 2018 12:25 pm

christian viladrich wrote:
Sat Oct 13, 2018 12:21 pm
Just wondering whether you could apply some heat arround filter n1 ? Maybe there is some glue ?
Yes, that is another possibility, can't see the glue if I look in the tube, but most of the times it is somehow glued. Have got another gold tube of a PST lying around here, will check later if they are the same size. If so, even destroying one of them means I can still rebuild the CaK to it's original state.

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Re: Dismantling and modification of a PST CaK

Post by TheSkyBurner » Sat Oct 13, 2018 2:40 pm

it looks like the important filter you want is stuck in the tube, you gotta remove the blue anodized ring to get it out. You need a strap wrench!

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Re: Dismantling and modification of a PST CaK

Post by bart1805 » Sat Oct 13, 2018 2:47 pm

I know Apollo, and I have tried it with a strap wrench. Have freed 2 PST etalons with it without major problems, but this one hates to be liberated.
Here is the last light of the PST CaK. Could not get into focus, so removed the upper part of the eyepiece holder. Asi290mm with a single Baader CaK filter.

ImageSun_10121243161_PSTCaK_BaaderCaKsingle by bart moors, on Flickr


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Re: Dismantling and modification of a PST CaK

Post by christian viladrich » Sat Oct 13, 2018 4:42 pm

So, finally there are two filters :
- Number 2 at the rear. Actually it consists in two parts (glued ?).
- Number one at the front (behind the lens ?), this one is a GG395 according to the information given by Apollo.
Is this correct ?
No filter at the front of the eyepice ?
BTW, the lens seems to be a doublet ?
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Re: Dismantling and modification of a PST CaK

Post by marktownley » Sat Oct 13, 2018 4:50 pm

Yes, the lens is a doublet Christian
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Re: Dismantling and modification of a PST CaK

Post by TheSkyBurner » Sat Oct 13, 2018 5:03 pm

christian viladrich wrote:
Sat Oct 13, 2018 4:42 pm
So, finally there are two filters :
- Number 2 at the rear. Actually it consists in two parts (glued ?).
- Number one at the front (behind the lens ?), this one is a GG395 according to the information given by Apollo.
Is this correct ?
No filter at the front of the eyepice ?
BTW, the lens seems to be a doublet ?
Christian
There are two filters in the eyepiece barrel, one is a clear square 6mm x 6mm, 2mm thick coated with Gold. Visually it has zero affect on color, so it must only be for infrared.

The second is a 6mm diameter round, that is a also a cemented stack. Equal in color(violet) and degradation to the larger stack but the glass is slightly thicker. The intensity seems equal to the larger one..

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Re: Dismantling and modification of a PST CaK

Post by bart1805 » Sun Oct 14, 2018 1:43 pm

Free at last!
Good day today. First tried to dismantle the Lunt B600 diagonal.
With a lens spanner it is really easy to twist the retaining ring of the BF:

Image20181014_141955_resized by bart moors, on Flickr

And there lies the square Lunt Blocking filter:

Image20181014_142039_resized by bart moors, on Flickr

Loosen the two screws on the diagonal and torch it a bit. Then the cell comes out, here you see it upside down. Look at the amount of glue that was used.

Image20181014_153708_resized by bart moors, on Flickr

It is just glued on the diagonal, the two screws are extra. So no thread:

Image20181014_152027_resized by bart moors, on Flickr

And after this used the Ruler-method to twist the retaining ring of the #1 PST CaK filter. If you have a good grip, it is really easy. That is it for today: a free Coronado and a free Lunt CaK filter. The #1 filter was lightly glued to the retaining ring, you can see the residu.

Image20181014_151818_resized by bart moors, on Flickr

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Re: Dismantling and modification of a PST CaK

Post by bart1805 » Sun Oct 14, 2018 5:52 pm

Here you can see that the Lunt filter consists of two pieces:

Image20181014_190801_resized by bart moors, on Flickr

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Re: Dismantling and modification of a PST CaK

Post by TheSkyBurner » Sun Oct 14, 2018 9:30 pm

Good ol' GG 395 glass :)

The lunt version is a stack of two pieces, Im not sure what the second filter is. But the pst yellow is rejection band coated gg395

I assume the lunt filter is glued/cemented to a coated piece of precision cut fluorite, refractive indexed for 393nm...

Its very humorous that lunt b600 is equal in price to an entire coronado pst complete telescope. The Uv400 objective lens on the telescope alone cost $250 retail by itself, and the pentaprism is another $100. That does not include the mount either. The cnc milled aluminum black box, well that would cost another $200 if you were to get somebody to make it with anodizing..... So without the four pst filters you are already exceeding $500 in part cost.

I have no idea how they priced the pst the way it is when you start getting these items manufactured on your own, it seems like somewhere on earth is a slave labor camp making the parts...

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Re: Dismantling and modification of a PST CaK

Post by bart1805 » Sun Oct 14, 2018 9:46 pm

250 dollar for that 40 mm objective lens? That is quite a lot, did not know that. Have two of them, so maybe I will make a UV optimised bino with them. (-;
I found it typical that the #1 filter is glued to the retaining ring where the #2 filter is not. Any particular reason you know of?

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Re: Dismantling and modification of a PST CaK

Post by TheSkyBurner » Mon Oct 15, 2018 12:34 am

bart1805 wrote:
Sun Oct 14, 2018 9:46 pm
250 dollar for that 40 mm objective lens? That is quite a lot, did not know that. Have two of them, so maybe I will make a UV optimised bino with them. (-;
I found it typical that the #1 filter is glued to the retaining ring where the #2 filter is not. Any particular reason you know of?
yea it sounds ridiculous but its true. These 400nm objectives are not cheap to source at all! I made a UV optimized collimator system for one of my other projects using the two objectives. Called the stage4 x-truder. I have all the measurements if you want to use it as a 393 barlow, but it make the system way longer. (the image is awesome though)

Just check out the prices on a single negative element, then add a second element positive element Thats the cost of the doublet....

https://www.cvilaseroptics.com/plcc-uv- ... ncave_lens

https://www.cvilaseroptics.com/plcx-uv- ... x_lens_UVL

So just for the two parts to make the objective is $400.00 , So how did meade doit? They did not make too many of those CaK telescopes.

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Re: Dismantling and modification of a PST CaK

Post by TheSkyBurner » Mon Oct 15, 2018 5:19 am

here is the relay lens calculation formula if you want to use the pst objective lens as a barlow.
So if the objective is 400mm away from solar focus, you can determine the new focal length quite easily to your ccd. (5.66x at 457mm)
focal length extender formula.PNG
focal length extender formula.PNG (27.19 KiB) Viewed 854 times

link to the x-truder mod I made using this method.
viewtopic.php?f=9&t=24503

picture of the x-truder (3100mm F.L without the second objective) 5.66x mag at 18 inches.
Image

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Re: Dismantling and modification of a PST CaK

Post by bart1805 » Sun Oct 21, 2018 10:15 am

Even after applying some heat on the blue collar of the PST CaK I could not remove it from the black box. So removed the lens and put it in a gold tube of a H-alpha PST. The difference in coatings is clearly visible. On the left the CaK objective.

Image20181021_114011_resized by bart moors, on Flickr

So now I have got clouds and and ready to go 40mm CaK telescope. From left to right after the gold tube:
- Adapter made by AOK
- JMI EV focuser
- Baader 2 inch clicklock
- 1,25 inch Skybender
- ASI 290mm

Image20181021_120317_resized by bart moors, on Flickr

Image20181021_120334_resized by bart moors, on Flickr

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Re: Dismantling and modification of a PST CaK

Post by TheSkyBurner » Sun Oct 21, 2018 11:39 pm

Thats going to be a fun scope

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Re: Dismantling and modification of a PST CaK

Post by marktownley » Mon Oct 22, 2018 6:02 am

I replaced the objective in my sm40 for one from a Cak PST too 😉
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Re: Dismantling and modification of a PST CaK

Post by TheSkyBurner » Thu Oct 25, 2018 6:18 am

so i figured out the best way to remove a locked pst tube.

You need to find a pipe vice. The bottom portion of this photo, the three finger jaws. Use a bicycle inner tube to prevent tube marring. That blue collar will pop right off with one single twist.

Image

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Re: Dismantling and modification of a PST CaK

Post by bart1805 » Thu Oct 25, 2018 7:36 pm

TheSkyBurner wrote:
Thu Oct 25, 2018 6:18 am
so i figured out the best way to remove a locked pst tube.

You need to find a pipe vice.
Yep, that looks good. But with the ruler method it is not really necessary to remove the tube. But would be handy for a regular PST. Thanks!

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Re: Dismantling and modification of a PST CaK

Post by bart1805 » Sat Nov 03, 2018 3:42 pm

The second PST CaK will be here in about two weeks I think. Thanks to Apollo and Marty I found the right filter cell for the 25mm PST #1 filter.
Here is how it looks now:

ImageCaKfilter_annotated by bart moors, on Flickr

The Lunt B600 can be replaced by the second PST #1 filter. And will have to experiment with one or two of the single Baader CaK filters. Etc.

And the PST CaK mod:

Image40mm_annotated by bart moors, on Flickr

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Re: Dismantling and modification of a PST CaK

Post by marktownley » Sat Nov 03, 2018 3:46 pm

Nice creations Bart!
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Re: Dismantling and modification of a PST CaK

Post by bart1805 » Sat Nov 03, 2018 4:19 pm

marktownley wrote:
Sat Nov 03, 2018 3:46 pm
Nice creations Bart!
Thanks Mark. Tomorrow, if the weather permits, will test it with the Bresser 127mm f/10.

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Re: Dismantling and modification of a PST CaK

Post by TheSkyBurner » Sat Nov 03, 2018 7:27 pm

bart1805 wrote:
Sat Nov 03, 2018 3:42 pm
The second PST CaK will be here in about two weeks I think. Thanks to Apollo and Marty I found the right filter cell for the 25mm PST #1 filter.
Here is how it looks now:

ImageCaKfilter_annotated by bart moors, on Flickr

The Lunt B600 can be replaced by the second PST #1 filter. And will have to experiment with one or two of the single Baader CaK filters. Etc.

And the PST CaK mod:

Image40mm_annotated by bart moors, on Flickr


A neat trick, use the thread rings from the filter holders to place a 25mm erf in the nose piece of the skybender. The inside of the nose is tall enough to hold a 25mm kg3 and also a second filter of your choice. Also if you want, you can put a concave element in there...

You can totally eliminate that baader planetarium K-filter (i would resell it), put the pst filter in the tilter instead so you can take blue wing images with a couple twists..

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