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PST Mod Query and update

Posted: Sun Jan 08, 2017 11:00 am
by Sungrazer
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

Re: PST Mod Query and update

Posted: Mon Jan 09, 2017 3:22 am
by Merlin66
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.