BluewaterObserva
Post Laureate
Reged: 05/18/04
Posts: 4763
Loc: Zuni Mtns, NM
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Anybody doing this sort of thing? What I am looking for is a basic large FL that would use all the available field stop of a Vixen R200S astrograph focuser. Like 2.7"-ish or so.
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Wes James
Carpal Tunnel
Reged: 04/12/06
Posts: 2454
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Contact Harry Siebert... he specializes in special order/custom eyepieces. You can see his website/access his contact information here. As his website says- "Things and services you can't get anywhere else".
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Wes
Atlantic Beach, FL
Some bino’s from Miyauchi 5x32 Binon's up through Garrett 20x110 Signature's,
Some telescopes from a Stellarvue 80mm NHNG up through a couple of 8” reflectors…
And a wonderful 4.25" Delmarva Shiefspiegler!
Some good friends, made here on C/N.
Oh- several cats and a wonderful wife!
Anyone want a cat???? :-O
"When your work speaks for itself- Don't Interrupt" -Gamble Rogers
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BluewaterObserva
Post Laureate
Reged: 05/18/04
Posts: 4763
Loc: Zuni Mtns, NM
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Thanks.. Sounds like a great place to start with it.
I actually figured in this forum, somebody would tell me of a way to make one myself for like $10. 
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llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 10459
Loc: Amargosa Valley, NV, USA
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You probably could, but it wouldn't be multi-coated.
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"S.O.E." (Sauron's Other Eye) 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Next Project: The "Eye of Sauron" Observatory!
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BluewaterObserva
Post Laureate
Reged: 05/18/04
Posts: 4763
Loc: Zuni Mtns, NM
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To be used on a 30" newt, I'd say the coatings may prove improtant. Mostly fainter objects / starfields though for sure with it.
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BluewaterObserva
Post Laureate
Reged: 05/18/04
Posts: 4763
Loc: Zuni Mtns, NM
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Not to much call for such a thing I take it?
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BluewaterObserva
Post Laureate
Reged: 05/18/04
Posts: 4763
Loc: Zuni Mtns, NM
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Any good links to basic eye piece making? Design?
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llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 10459
Loc: Amargosa Valley, NV, USA
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You could start with Texereau, of course. I don't have any web-derived savvy about it, but Google might help.
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"S.O.E." (Sauron's Other Eye) 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Next Project: The "Eye of Sauron" Observatory!
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BluewaterObserva
Post Laureate
Reged: 05/18/04
Posts: 4763
Loc: Zuni Mtns, NM
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I did some googles, and really did not find what I was looking for.
Certainly not enough to tell me what element(s) I would need for the desired field stop, ect..ect.. I mean, I do understand the most basic aspect of how an eye piece works already.
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 817
Loc: Houston,Texas
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There's a fellow down in Austraila that has a large ATM web site...the name fails me currently and is bookmarked in another computer...but he goes about giving a full description of just how to design large observatory eyepiesce in great detail...including design ideas and help
I'll look over the weekend
Regards,
Preston
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A few I enjoy,
and a few more in the works ;<)
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GlennLeDrew
professor emeritus
Reged: 06/18/08
Posts: 608
Loc: Ottawa, Ontario, Canada
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If I recall correctly, your 'scope is in the f/4 range, and has a pretty large secondary obstruction. To get such a large linear field of view as you desire (~2.7"), you'll have to make an eyepiece with a focal length long enough to both:
1) have a field stop as large as ~2.7", and
2) have an exit pupil large enough so that the annulus which lies outside the exit pupil's central obstruction is, say, at least 4mm wide.
Point #2 is based on your desire to get a whopping 2.7" diameter field. You couldn't get or make an eyepiece to both do this *and* have a short enough focal length so as to keep the exit pupil under 7-8mm. To meet this criterion at f/4, the longest f.l. eyepiece you could use would be 28-32mm. But the largest linear field you can get at such a f.l. is ~2".
So your other option, though less desirable, is to go with a much longer f.l. which will give a *huge* exit pupil of about 15mm or so. The appropriate f.l. would be ~60mm. In this way you'd be able to "look around" the central obstruction, which would be just like using an off-axis mask (as typically used to improve image sharpness if optics and/or seeing are bad.)
As a start, you could use a pair of junked 35mm binocular objectives. They have focal lengths of about 140mm. A pair, mounted together so that their front surfaces (more strongly curved than the back surfaces) are facing each other, and with a small space between. This would be much like a Plossl eyepiece, and the combined focal length would be 140mm/2 = 70mm, or close to what you'd need.
But why go through these hoops? You'll in effect be using a *very* much smaller aperture telescope, of about 2.5-3". Why not use a small refractor or large binocular instead? You'll probably be able to get as wide--or wider--an angular field at the same magnification.
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Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV
Mediocre minds discuss people. Good minds discuss events. Great minds discuss ideas.
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jdownie
professor emeritus
Reged: 02/24/06
Posts: 734
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Check out Bob May's 200" scope project - he made his own large eyepieces for it.
http://stellafane.org/post_conv/2001_conv/2001_all_scopes06.html
John
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ATM project - a terrible waste of good Pyrex.
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BluewaterObserva
Post Laureate
Reged: 05/18/04
Posts: 4763
Loc: Zuni Mtns, NM
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Thanks a million for the additional posts on this.
I think I have a grasp on what to at least try with it.
I am thinking something around the 50mm range. I understand the exit pupil will be very large.
It does OK, with just the largest Pentax XL...
We are really talking about using it for the largest of objects. M31 as an example, just isn't really doing it for me with the limited real FOV I am getting right now.
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