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Author Topic: C11 and PST  (Read 2960 times)

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Offline Isla Bonita

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C11 and PST
« on: 12:51:56, 17 September, 2012 »
Hi All
I understand that the PST is optimised as a f10 instrument.
I have seen a number of PST conversions to larger telescopes.
Is it feasible to fit an 80mm ERF to an aperture in a blank fastened  infront of the corrector plate of a C11 and use the etalon body of the PST in the 2" eyepiece tube.
Has anyone tried this? Is it feasible bearing in mind the safety implications of firmly attaching the optical components.


Dave H

Offline Nomis Elfactem

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Re: C11 and PST
« Reply #1 on: 13:45:57, 17 September, 2012 »
Hey Dave - the key thing here is that the light cone entering the PST is at f/10... technically what you are suggesting can be done (bearing in mind all the obvious safty implications) as the Baader ERF's are 90mm so you could have an offset opening into the C11 that is say 85mm.  This would then mean though you would need a focal length of 850mm for get the f/10 required for the PST. 

My understanding however is that the native f/l of the C11 is 2800mm (giving it a f/10 rating with an aperture of 280mm) but that won't be it's f/ratio if you step it down to 80mm.  By my calculations it will be running at f/32 (2800mm / 85mm) which is no good for the PST.  You could however use a x0.3 focal reducer to get to f/10 (if such a thing exists ?) but that's a lot of glass in the imaging train !

Now, if you were to put a 280mm ERF on the front then that's a totally different kettle of fish and something I'd really like to see   :scare: :urock: :thumbup:


Scopes: Astro-Tech AT-111EDT Triplet, TS65ED Quad, Orion ST80, Modded PST-90 Solar Scope, PST Cak (on loan)
Cameras: SXVF H694, Atik 16ic, Canon EOS 600d, DMK41, DMK21, QHY 5L-II (mono & colour)
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Offline Merlin66

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Re: C11 and PST
« Reply #2 on: 17:47:47, 19 September, 2012 »
Yes, SCT's have been used as "donors" for PST Mods.
Simon, the f10 is a minimum, the mod will still work with higher f ratios. Mind you, I don't think I've tried at f30!!
The critical issue is being able to position the PST etalon at -200mm from the prime focus.
(This is well nigh impossible when a reducer is used)
To check, set up an eyepiece at the end of a 200mm extension and see if you can still focus ie on the moon etc.
C11, C9.25 SCT, 4" Genesis, NEQ6pro, modded 1000D,  ATik314L+, DMK41AF04, SM60DS/BF15, and Spectroscopes (many!).
"Astronomical Spectroscopy for Amateurs", "Grating Spectroscopes-How to Use them" -Springer

Offline Isla Bonita

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Re: C11 and PST
« Reply #3 on: 12:55:33, 20 September, 2012 »
Thanks Guys
I will try the 200mm extension this weekend and take it from there.
Best regards
Dave H

Offline dm-mas

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Re: C11 and PST
« Reply #4 on: 23:39:05, 13 December, 2012 »
Hmmm, bit late jumping in on this one but....

I've been thinking of using a 6" SCT for a PST mod - Two reasons for this, 1- I've seen it done so I know it'll work.  ;) & 2-I've already got a 6" ERF.  :D

All I need now is the funding.  :(

And the scope.

And the PST.

I can see this one taking a while.  :wounded:

EQ6 pro & home made pier, with various combinations of the following... 8" & 12" LX200 OTA's, Orion ED80, TS65 quadruplet & Meade AR6 150mm refractors,Orion optics 6" F4 & GSO 8" F4 newts, Coronado Maxscope 60, DMK21 & 41, QHY8, modded 350D, Atik 314L. And not enough space to keep it all in!!!


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