PST Mod Query and update

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Sungrazer
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PST Mod Query and update

Post by Sungrazer » Sun Jan 08, 2017 11:00 am

Hi All

the parts are coming together the for the PST Mod.

I have the 75mm blocking filter, mounting bracket and pst attachment as recommended from http://www.teleskop-austria.com/

Proposed Donor scopes:
I have an ED80 which is f7.5 - which will give me an F8 scope with the 75mm ERF.
I just picked up a second hand skywatcher acromat 80mm (native f11.3 and an 86mm tube but a 1 1/4 eyepiece so it needs a 2" focusser). Stopped down to 75mm will give me F12.

I can't seem to get focus with the ED 80 and I can't test the 80mm acromat until I get a 2inch focusser for it.

My Qns are

which one do you think will give the best results? I know i need at least F10 so the ED80 is probably out but I recall Valery saying somewhere that F12 was not so good either??
is it worth spending the $ to buy the focusser (or does anyone have one lying around they don't need having upgraded their own focussers.
Will I have to cut the 80mm acromat tube shorter do you think?

Any suggestions will be much appreciated.

cheers
Karen
PST Double stacked usually on an EQ3, ZWO174mm, DMK21AU, QSI683wsg, MeadeLX200, ED80 on an EQ6, and some other stuff

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Merlin66
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Re: PST Mod Query and update

Post by Merlin66 » Mon Jan 09, 2017 3:22 am

Karen,
The 80mm f11.3 will work well.
It's similar to the f11 TS 102 I use.
Why worry about a focuser? You'll only use it once to set the etalon position and it will never move....
You'll probably have to cut 50-75mm of the OTA to get the etalon at the correct -200mm inside prime focus.
You can use a thick (Say 50mm) wooden plug in the end of the OTA drilled with a 2" central hole to fit the nosepiece. Slide the etalon assembly to focus then clamp it in final position.
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