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 1562 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 TheSkyBurner » Sun May 06, 2018 12:14 am

Bob Yoesle wrote:
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..
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?

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Re: PST CaK mod

Post by TheSkyBurner » Sun May 06, 2018 12:17 am

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?

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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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Re: PST CaK mod

Post by TheSkyBurner » Sun May 06, 2018 11:40 am

Your filter train is substantially different than mine. I only have the fist threaded adapter in my pst’. Dont know what that second filter holder you have is, but in my system the first filter is about 2mm seperate from the second filter and bothe in the same cell. Seperated by a single spacer ring. The last filter in your eyepiece holder is a secondary 5mm band blocker attatched to a shortpass filter.

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Re: PST CaK mod

Post by TheSkyBurner » Sun May 06, 2018 11:42 am

Also whhat is that white adapter? Did you add that cuz its not supposed to be there. This pst is rather butchered!

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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 TheSkyBurner » Fri May 11, 2018 12:33 am

merlin: the pst cak filter is not the same as the pst ha filter. It threads on the inside of the gold tube, it is seperate from the blue ring.

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Re: PST CaK mod

Post by TheSkyBurner » Fri May 11, 2018 12:42 am

002.jpg
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001.jpg
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003.jpg
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Re: PST CaK mod

Post by TheSkyBurner » Fri May 11, 2018 12:45 am

the gold tube thread is m50 male, and the blue ring that goes over the gold thread is m50 female.

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Re: PST CaK mod

Post by TheSkyBurner » Fri May 11, 2018 12:50 am

the Cak filter thread is 46mm male
pstcakthread.jpg
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Re: PST CaK mod

Post by TheSkyBurner » Fri May 11, 2018 12:55 am

merlin66 : gold tube thread at 50mm.. With this information you can make a very quick and easy attachment using off the shelf standard camera supplies. 48-52mm camera thread ring, 52mm extension barrels, 52mm to 46mm step down ring. 46-48mm nosepiece etc.
pstgoldthread50mm.jpg
pstgoldthread50mm.jpg (354.61 KiB) Viewed 1449 times

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Re: PST CaK mod

Post by TheSkyBurner » Fri May 11, 2018 1:19 am

you dont need the eyepiece holder anymore, just ditch that. All you need is the blue filter and some kind of erf system in front of it like bob states. Baader planetarium 1.25" U filter will work. The system will never be visual however so keep that in mind.

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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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Re: PST CaK mod

Post by TheSkyBurner » Fri May 18, 2018 12:37 am

I would bin them and replace the whole eyepiece holder section with a 1.25" filter holder relying on a edmund optics 394nm hard coated filter.

if you wish to replace the rusted filter, find the meier optical 393nm bandpass filter ,
http://maierphotonics.com/bandpass-filter.aspx Item Number: 393BW10/12

The second filter in the eyepiece holder cannot rust, it is just a piece of dark yellow glass and you can probably clean it very well if you are careful, it is most likely some kind of standard glass based 400nm shortpass filter.

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Re: PST CaK mod

Post by TheSkyBurner » Fri May 18, 2018 2:46 am

ill put together a parts list with links to rebuild the whole thing, just need a couple days to research more options.

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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 TheSkyBurner » Fri May 18, 2018 9:34 pm

Bob Yoesle wrote:
Fri May 18, 2018 7:27 pm


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.
Bob, did your PST not have a filter before the blue filter? I consider the "rusted primary" filter to be filter 1, and the filter behind this to be filter 2. So it is important to an extent to separate the two, because one of them is guaranteed to suffer degradation and the other is not.
cak 2 and2b.jpg
cak 2 and2b.jpg (126.12 KiB) Viewed 1180 times
cak 2 and 1.jpg
cak 2 and 1.jpg (112.38 KiB) Viewed 1180 times

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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 1028 times
No 2 PST CaK filter.jpg
No 2 PST CaK filter.jpg (194.6 KiB) Viewed 1013 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 TheSkyBurner » Tue Jun 12, 2018 6:13 am

Okay so I spent some time over looking this and Came up with the easiest, non-destructive method to mod you PST CAK etalon.

Using the same 48 - 46mm downsizing ring I mentioned in a previous post, take a small hand held grinding stone and strip away about 25 passes on the inside portion of the 48mm section. The etalon will then slip nicely through the 48mm section; thus allowing you to thread it on to 46mm section in reverse. Now you can mate it inside any 2" eyepiece barrel . Simple quick and easy, off the shelf.


Here is the etalon mounted inside of my golden skybender! Now its one of a kind.
Cak PST reverse 48 - 46mm thread mod skybender  A.jpg
Cak PST reverse 48 - 46mm thread mod skybender A.jpg (124.84 KiB) Viewed 681 times
Cak PST reverse 48 - 46mm thread mod skybender  B.jpg
Cak PST reverse 48 - 46mm thread mod skybender B.jpg (111.39 KiB) Viewed 681 times

Here is the etalon showing how I used the easiest route humanly possible, by flipping the sizing ring.
reverse 48 - 46mm CaK pst mod A.jpg
reverse 48 - 46mm CaK pst mod A.jpg (193.97 KiB) Viewed 681 times
reverse 48 - 46mm CaK pst mod B.jpg
reverse 48 - 46mm CaK pst mod B.jpg (188.59 KiB) Viewed 681 times
reverse 48 - 46mm CaK pst mod C.jpg
reverse 48 - 46mm CaK pst mod C.jpg (187.62 KiB) Viewed 681 times

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Re: PST CaK mod

Post by TheSkyBurner » Fri Jun 15, 2018 11:05 pm

Double stacked CaK Pst skybender mod!
double stacked Skybender CaK pst mod A.jpg
double stacked Skybender CaK pst mod A.jpg (183.61 KiB) Viewed 573 times
double stacked Skybender CaK pst mod B.jpg
double stacked Skybender CaK pst mod B.jpg (219.28 KiB) Viewed 573 times

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