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Questions & Answers/Tips & Tricks => Telescope/Equipment/Accessories => Solar Equipment => Topic started by: JohnM on 20:48:10, 02 April, 2011

Title: Double etalons on a PST
Post by: JohnM on 20:48:10, 02 April, 2011
I wonder how he made this connection.
It seemed to work.
http://www.hkastroforum.net/viewtopic.php?t=22152&start=0&postdays=0&postorder=asc&highlight=&sid=06eae131443347706d1e4a5c508fc975
Title: Re: Double etalons on a PST
Post by: Nomis Elfactem on 21:17:12, 02 April, 2011
Looks like a custom made adapter.  Ken has done this - what did you use Ken ?

S.
Title: Re: Double etalons on a PST
Post by: Merlin66 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.....
Title: Re: Double etalons on a PST
Post by: JohnM 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.
Title: Re: Double etalons on a PST
Post by: Merlin66 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?
Title: Re: Double etalons on a PST
Post by: JohnM 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.
Title: Re: Double etalons on a PST
Post by: Merlin66 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.)
Title: Re: Double etalons on a PST
Post by: Nomis Elfactem 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 !
Title: Re: Double etalons on a PST
Post by: JohnM 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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