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Author Topic: Double etalons on a PST  (Read 1862 times)

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Offline JohnM

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Offline Nomis Elfactem

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Re: Double etalons on a PST
« Reply #1 on: 21:17:12, 02 April, 2011 »
Looks like a custom made adapter.  Ken has done this - what did you use Ken ?

S.
Simon

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)
Accessories: SX USB Filter Wheel, SX OAG, Baader LRGB Ha SI OII Filters, SharpSky Focuser
Mount: EQ6 (EQMOD), SW Star Adventurer, plus a lot (and I mean a lot) of other bits and pieces

Offline Merlin66

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Re: Double etalons on a PST
« Reply #2 on: 03:54:34, 03 April, 2011 »
Looking at the image of his scope he's used some plastic material to jamb them together.
I made up a M50 threaded adaptor which holds both etalons rigidly and aligned. (Sketch available - actual adaptor available to "borrow" for limited trials ;-)  )
He got some good results with his set-up though!! Not the easiest thing to tune.....
C11, C9.25 SCT, 4" Genesis, NEQ6pro, modded 1000D,  ATik314L+, DMK41AF04, SM60DS/BF15, and Spectroscopes (many!).
http://tech.groups.yahoo.com/group/astronomical_spectroscopy/
"Astronomical Spectroscopy for Amateurs", "Grating Spectroscopes-How to Use them" -Springer

Offline JohnM

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Re: Double etalons on a PST
« Reply #3 on: 12:45:22, 03 April, 2011 »
I'm going to try and contact him and see if I can get any more info.
Especially about the front and rear lenses of the etalon.

Offline Merlin66

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Re: Double etalons on a PST
« Reply #4 on: 13:55:32, 03 April, 2011 »
John,
What info are you looking for, maybe I can help.
The etalon has a -200mm lens on the front and a +200mm lens on the rear.
Does this help?
C11, C9.25 SCT, 4" Genesis, NEQ6pro, modded 1000D,  ATik314L+, DMK41AF04, SM60DS/BF15, and Spectroscopes (many!).
http://tech.groups.yahoo.com/group/astronomical_spectroscopy/
"Astronomical Spectroscopy for Amateurs", "Grating Spectroscopes-How to Use them" -Springer

Offline JohnM

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Re: Double etalons on a PST
« Reply #5 on: 14:15:58, 03 April, 2011 »
I just want to know if he had to remove/change either of the elements and if he did any calculations on the distance the two etalons were separated.
Seems like if the + and - elements were left in place on both, the light beam couldn't be kept in focus.
This guy is from Hong Kong and has been posting some fine images at Cloudy Nights for quite a while.
There is a new moderator for the CN Solar forum and for some reason the link showing his mod wasn't immediately deleted like they usually are.

Offline Merlin66

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Re: Double etalons on a PST
« Reply #6 on: 16:12:27, 03 April, 2011 »
John,
There are only a couple of options available, in both cases the etalons must be placed as close as physically possible:
1.The front and rear lenses are left on both etalons this allows a parallel collimated beam to pass through both etalons and focus 200mm behind the last element.
2. Remove the rear positive element from the first etalon and the front barlow element from the front of the second etalon; this would still give a collimated beam through both etalons and still focus 200mm behind the last element.
(I've considered this second option, and found I could get into the rear positive element and remove the holding ring...but I didn't have the same success with the front barlow element so didn't go any further.)
C11, C9.25 SCT, 4" Genesis, NEQ6pro, modded 1000D,  ATik314L+, DMK41AF04, SM60DS/BF15, and Spectroscopes (many!).
http://tech.groups.yahoo.com/group/astronomical_spectroscopy/
"Astronomical Spectroscopy for Amateurs", "Grating Spectroscopes-How to Use them" -Springer

Offline Nomis Elfactem

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Re: Double etalons on a PST
« Reply #7 on: 16:16:11, 03 April, 2011 »
John - as the front -200 is a collimating lens then I don't think he will have had to change anything... the +200 lens at the back of the first etalon will just start to angle the cone in (to focus) but if the two lenses are pretty close together the second etalon front lens will just re-collimate and "Bob's your uncle"....

S.

EDIT: Just seen Kens post.... this is option 1 !
Simon

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)
Accessories: SX USB Filter Wheel, SX OAG, Baader LRGB Ha SI OII Filters, SharpSky Focuser
Mount: EQ6 (EQMOD), SW Star Adventurer, plus a lot (and I mean a lot) of other bits and pieces

Offline JohnM

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Re: Double etalons on a PST
« Reply #8 on: 16:25:23, 03 April, 2011 »
I guess I missed out on a good deal on new PSTs here in the US.
A dealer had them for $400 last winter, but they're now back up to $750.
If I can run across a used one for a good price it might be worth buying another to try the doubled etalons,
Until this weather here settles down I think I'll stay with the project I have going.

 

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