What scope for the PST Mod?

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Dark Neptune
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What scope for the PST Mod?

Post by Dark Neptune » Sat Jun 20, 2015 8:40 am

Hello, I am new here.

Was introduced to this forum via a solar guru from Singapore, about modding my PST. After being seduced, decided to commit to this new venture to mod my PST.

I would like to seek recommendations for the larger OTA for mod. Would a SkyWatcher 4" F/9.8 Achro work? I have to sell away my Celestron Nexstar Evolution 6 to fund this venture, thus can't overspend, since I still need to get an ERF afterall. Any thoughts from the professionals here would be appreciated, thanks! :D

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Re: What scope for the PST Mod?

Post by swisswalter » Sat Jun 20, 2015 11:48 am

Hi Neptun

welcome to that wonderful site. Have fun modding your scope. Your achro will work perfekt. Make sure you can reach with the etalon the point -200 mm from the focal spot
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Re: What scope for the PST Mod?

Post by Dark Neptune » Sat Jun 20, 2015 1:18 pm

swisswalter wrote:Hi Neptun

welcome to that wonderful site. Have fun modding your scope. Your achro will work perfekt. Make sure you can reach with the etalon the point -200 mm from the focal spot
Hello, thanks for the reply!

I was reconsidering, and thinking of getting a SkyWatcher 90mm achro refractor instead, for the following reasons:

1. Cheaper.
2. While the Focal Ratio for the 102mm is f/9.8, the 90mm is f/10.
3. I plan to get the Baader ERF, whose diameter is 90mm. So having a scope 12mm larger in diameter does not make any difference.

What do you think?

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Re: What scope for the PST Mod?

Post by marktownley » Sat Jun 20, 2015 1:38 pm

Whichever scope has the best focuser is the one I would go for...
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Re: What scope for the PST Mod?

Post by Dark Neptune » Sat Jun 20, 2015 2:32 pm

Hello Mark,

The 102 has a 2" R&P, while the 90 has a 1.25" R&P. :(

I am unsure whether spending more on better focuser is worth it.

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Re: What scope for the PST Mod?

Post by marktownley » Sat Jun 20, 2015 2:44 pm

The focuser is key in a PST mod, the better it is the better the results. I would not bother at all with the 1.25" focuser.
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Re: What scope for the PST Mod?

Post by swisswalter » Sun Jun 21, 2015 6:20 am

Hi Neptun

Mark is right. In your case, the focuser is the key
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

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Re: What scope for the PST Mod?

Post by Dark Neptune » Wed Jun 24, 2015 12:54 pm

Hello,

there's also the issue of optical axis misalignment, do you all have any advice on how to overcome that obstacle? Thanks!

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Re: What scope for the PST Mod?

Post by Merlin66 » Wed Jun 24, 2015 3:33 pm

You can successfully mod a donor without the need for a focuser on the OTA.
I agree, behind ( between the etalon and the eyepiece/ camera) the etalon, you will need a good focuser (if using the Stage 2 mod).
I use the Borg non-rotation helical focusers....
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Re: What scope for the PST Mod?

Post by Dark Neptune » Mon Jun 29, 2015 1:39 pm

About to make my purchase. So far here's the items in my cart

- OEM (TS) 90mm f/10 achro OTA
- Vixen dovetail for the 90mm
- Baader ERF 90mm
- Holding cell for the ERF

Anything else that is mandatory? This is a stage 1 mod I am doing, on a budget. Thanks!

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Re: What scope for the PST Mod?

Post by marktownley » Mon Jun 29, 2015 4:14 pm

Looks good, just a nosepiece to add the PST body to the focuser. Is the focuser 2"?
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Re: What scope for the PST Mod?

Post by Dark Neptune » Tue Jun 30, 2015 4:24 am

Nope, just 1.25". :(

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Re: What scope for the PST Mod?

Post by marktownley » Tue Jun 30, 2015 7:40 pm

I would get a scope with a 2" focuser. How do you plan to fix the PST body to the scope?
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Re: What scope for the PST Mod?

Post by astrohardy » Sat Jul 18, 2015 2:34 pm

Do you intend to use the refractor for anything else but H-alpha? If not: For our 70/700 PST "Sunlux" mod the host scope has a lousy 1.25" focuser. We simply cut the tube precicely that the backfocus (distance between the rear of the adapter and the focus) is identical to that of the golden tube of the PST. You can now use the focusing mechanism of the PST itself, and just need a sturdy adapter to connect the PST black box to the scope. This works very well.

Hartwig

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