PST CaK mod

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Marsman
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PST CaK mod

Post by Marsman » Sun Apr 29, 2018 8:17 pm

Hi all,
I have a Coronado CaK PSt.
The 5mm blocking filter in the eye piece holder is rusted.
I want to do a mod to turn the etalon into a single unit to fit a f7 90mm refactor thus removing the penta prism.
My questions are 1. what filters do I need to replace the 5mm blocker, (Baader 1.25" Calcium K-Line Filter 395nm good ? )
2. what and where to get a front 2" adapter, PST-50 from Telescope Austria fit the etalon ? or does this not fit.
3. adapters for the rear to fit a camera to.

Most posts I have found refer to the Ha version so a comprehensive post on this mod would be appreciated.

Regards
Paul

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Bob Yoesle
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Re: PST CaK mod

Post by Bob Yoesle » Tue May 01, 2018 1:21 pm

Forget using the PST body and make a completely new CaK "module" using some relatively easy to obtain 2" inch adapters.

You'll need a Baader or Astronmomic Blue CCD filter for use as an ERF, and the Baader CaK filter makes a good blocking filter for the "no. 1" narrow-band component of the PST:
CaK DS Module New SM.jpg
CaK DS Module New SM.jpg (331.04 KiB) Viewed 2252 times
Additional filters can be added for a narrower ERF pass-band if you go to a larger aperture, but these become more expensive.
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Re: PST CaK mod

Post by Marsman » Sun May 06, 2018 10:32 am

Hi Bob
This photo shows the filters in the optical train.
I have no parts that fit these threads , I guess a 2" barlow tube after the etalon would allow for the Baader filters to be fitted but I dont know what adapter to fit on the front to connect to a larger scope.
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20180506_111302.jpg
20180506_111302.jpg (2.76 MiB) Viewed 2177 times

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Re: PST CaK mod

Post by Marsman » Thu May 10, 2018 8:43 pm

Hi, the white is tape wrapped around the etalon. The butchered bit was caused by tools to remove the eye piece holder from the focus body ( too much thread lock ).

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Re: PST CaK mod

Post by Merlin66 » Fri May 11, 2018 12:31 am

Check the forum library for adaptors for the PST etalon. AOK Swiss can supply.
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Re: PST CaK mod

Post by Marsman » Thu May 17, 2018 6:26 pm

Hi TheSkyBurner, now we are getting to the info needed to mod this thing !
So all I need to know is , what are the last filters in the eyepiece holder ?
Do I need to replace them or bin them, remember the one nearest the penta prism is rusted.

Paul

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Bob Yoesle
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Re: PST CaK mod

Post by Bob Yoesle » Fri May 18, 2018 7:27 pm

Bob, what 2" filter adapters did you use? The CaK pst filter is not 2" and does not seem like it would be a drop in option?

Can you provide links to the actual products used that hold your dismantled PST parts I also notice in the picture you do not mention the pst #2 filter which is blue coated on yellow glass? I thought this is the actual narrowband hard coated narrow band filter? I was under the impression that the first filter in the array of the gold tube was just a sacrificial erf?
I use a standard 1.25 inch filter cell for the PST elements. I've used some scavenged parts and the Skybender unit, but will be revising this in the near future with a custom made set of components.

The only PST filter used is the "blue coated on yellow glass." Whether you call this the No. 1 or No. 2 filter is problematic, but inconsequential.
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Re: PST CaK mod

Post by Bob Yoesle » Wed May 23, 2018 1:44 pm

Yes, it did have that (deteriorated) shinny gold filter as well, which shows as a blue substrate and ITF-like deterioration from the edge inward when held just right:

Rusted CaK filter.jpg
Rusted CaK filter.jpg (20.5 KiB) Viewed 1720 times
No 2 PST CaK filter.jpg
No 2 PST CaK filter.jpg (194.6 KiB) Viewed 1705 times

My convention for the filter names is that the 1st filter after the objective is called the "No. 1 filter," which I believe you are calling the "No. 2" filter. This is the "magic filter" which passes the 2.2 A FWHM CaK 393 nm line, as well as a ton of additional longer wavelengths which must be filtered out...
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Re: PST CaK mod

Post by Marsman » Sat Oct 13, 2018 6:46 am

Ok great mod, now where can I get a sky bender from ?

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Re: PST CaK mod

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

Bob Yoesle wrote:
Fri May 18, 2018 7:27 pm
I use a standard 1.25 inch filter cell for the PST elements. I've used some scavenged parts and the Skybender unit, but will be revising this in the near future with a custom made set of components.
Hi Bob,
I tried a Baader and a Astronomik 1,25 inch filter cell, they are both too big. I suppose I need a "cheaper one" like this:
https://www.ebay.nl/itm/Venus-Planetary ... SwZ8ZW2db2
Baader and Astronomik clearly maximise the size and have tiny retaining rings, this one clearly does not. Am I correct?
Thanks and CS, Bart.

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Re: PST CaK mod

Post by george9 » Sun Oct 14, 2018 2:06 am

I made cardboard rings to hold the PST elements within the larger 1.25 inch cells. I actually exploited that to make a very compact tilt mechanism: I basically push the cardboard along the threads on one side compared to the other. It was meant as a prototype, but I haven't felt the need to upgrade it.

George

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Re: PST CaK mod

Post by bart1805 » Sun Oct 14, 2018 7:43 am

george9 wrote:
Sun Oct 14, 2018 2:06 am
I made cardboard rings to hold the PST elements within the larger 1.25 inch cells.
Thanks George! I was thinking about 3D printing some rings.

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Re: PST CaK mod

Post by Marsman » Sun Oct 14, 2018 7:41 pm

Hi
I have paid 160 as I see you only have 1.25 left but if you still have a 2 I would go fir it.
My address in 90 Mill Drove in the UK, if you need any further detail PM me.

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