MKV
Carpal Tunnel
Reged: 01/20/11
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: Mike I. Jones]
#5529904 - 11/20/12 11:30 AM
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Hi Mike. You're absolutely right about the trouble, cost, effort (never mind the ethics involved), etc. of retro-engineering registered products. What I had in mind was, of course, comparing your Rosin-type triple corrector to Paracorr and Wynne type condifugrations that have been suggested as possible close replicas of the same. In my relatively short time on CN, I remember both corrector types being mentioned and discussed, possibly some in archived files.
Mladen
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MKV
Carpal Tunnel
Reged: 01/20/11
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: Mike I. Jones]
#5529920 - 11/20/12 11:37 AM
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Mike I was told by a mod (not you) that one may not post someone else's picture (as an example), even in context - and even if crediting the author.
Mladen
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MKV
Carpal Tunnel
Reged: 01/20/11
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: Mike I. Jones]
#5529938 - 11/20/12 11:44 AM
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Mike, speaking of reto-engineering, some people obviously feel it's worth the effort.
http://img405.imageshack.us/img405/5439/es14ethos2.jpg
as seems to be the case with Ethos. Given this precedence, I am really surprised no one has come up with a Paracorr copy. Either it's not lucrative enough, or perhaps the laws have changed since this photo was taken.
Mladen
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Pinbout
Post Laureate
Reged: 02/22/10
Loc: Montclair
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: MKV]
#5530542 - 11/20/12 04:15 PM
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Quote:
some people obviously feel it's worth the effort.
http://img405.imageshack.us/img405/5439/es14ethos2.jpg
I've always heard about that image but never saw it. Thanks
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Gert
super member
Reged: 04/15/08
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: kfrederick]
#5531422 - 11/21/12 01:00 AM
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Hi Folks,
Is this configuration used by the ASA astrographs?
http://www.astrosysteme.at/eng/astrographs.html
...
H-SERIES
The astrograph of the H-Series have a hyperbolic primary mirror...
Clear Skies,
Gert
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Loc: Fort Worth TX
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: Gert]
#5531718 - 11/21/12 08:52 AM
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Who knows? Only the ASA folks, and they ain't tellin'!
It could very well be similar to the ASA designs. I could probably get a good DL-ish design at f/2.8 over the same field and spectral band, but it would be a real bear to build and keep in alignment. f/3.5 is plenty fast for me.
Mike
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Loren Chang
member
Reged: 04/28/09
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: Mike I. Jones]
#5533784 - 11/22/12 11:27 AM Attachment (48 downloads)
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Hello Mike,
A beautiful design, again. I found similiar ideas in my database. Post one of them only here. Dose this Ross corrector variant works on newtonian?
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MKV
Carpal Tunnel
Reged: 01/20/11
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: Loren Chang]
#5534176 - 11/22/12 04:22 PM
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Dose this Ross corrector variant works on newtonian?
Loren, I hope you won't mind if I jump in on this. In order to get this level of correction, the primary mirorr must be hyperboloidal. A Ross corrector reduces coma in a Newtonian (i.e. paraboloidal primary), but at the cost of introducing spherical undercorrection - which is offset by hyperboloizing (overcorrecting) the primary. But then it's no longer a Newotnian.
Maybe modern glass melts offer a possibility of creating a Ross/Rosin type corrector that would correct for coma in a Newtonian without significant spherical residual. It may be worth looking into this. Mike, what say you?
Mladen
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Loc: Fort Worth TX
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: MKV]
#5534576 - 11/22/12 10:45 PM
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I say, don't talk with your mouth full! Been enjoying family and food all day. I'll get back into CN maybe this weekend.
Gobble 'til ya wobble,
Mike
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Loren Chang
member
Reged: 04/28/09
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: MKV]
#5534955 - 11/23/12 07:30 AM
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In order to get this level of correction, the primary mirorr must be hyperboloidal. A Ross corrector reduces coma in a Newtonian (i.e. paraboloidal primary), but at the cost of introducing spherical undercorrection - which is offset by hyperboloizing (overcorrecting) the primary. But then it's no longer a Newotnian.
Hello Mladen,
Everyone is welcome. I understand what you said. For Newtonian, Wynne corrector gives excellent image but is diffcult to make. Ross corrector is simpler though causes spherical aberration. What I'm asking is will it be better to add one more element in Ross for newtonian?
Hello Mike,
Waiting for your comment! I'm playing a F/10 superachromat design in USP 2009/0296201. Take a look if you are interstring. I'll post it in another thread.
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MKV
Carpal Tunnel
Reged: 01/20/11
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: Loren Chang]
#5536700 - 11/24/12 07:07 AM
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Hi Loren. My point was that if you add a third element to a paraboloidal mirror you end up with a Wynne-type corrector.
_____
Hey Mike, I hope you had a nice Thanksgiving. It appears that your corrector's first surface (#4) is the "hairline trigger" that must be spot on to a very high precision - I mean a radius of curvature accurate to a few ten thousands of an inch. Vow!
Radii of the real element (#8 and 9) have more generous tolerances and could be used to counterbalance #4 with much greater radius tolerance.
But that means the radius of #4 must be known to better than 0.05%. Seems like this would be the first surface to be finished and then all other sufraces would be built around that one - again to very high precision.
I also find that perhaps thickness/spacings of the correctors elements must be in the range of ±0.0001 inch, and that the diffraction limited focal range is is in the order of only ±0.0005 inches.
As I said , this is just a preliminary look, using a slider wheel tool. Curious to see what your tolerance data will tell us.
Mladen
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Loc: Fort Worth TX
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: MKV]
#5536924 - 11/24/12 09:51 AM
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Just checking in briefly. Mladen, when you varied your slider wheels, what compensators did you use? You need to have compensators that can be easily changed during tolerancing, such as refocus, airspaces, etc. Otherwise you get just what you found, outrageously tight tolerances, when they needn't be. In this application, the BFL could vary a millimeter or so and have no impact on system utility. The BFL, airspaces and distance from the diagonal can all vary a small amount by re-optimizing. I will use all those values when I get back and study the tolerancing.
Mike
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MKV
Carpal Tunnel
Reged: 01/20/11
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: Mike I. Jones]
#5536964 - 11/24/12 10:15 AM
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Mike, you're so right. I overlooked the refocusing. My bad. Indeed, once you compensate, the tolerance range becomes more realistic.
Mladen
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ed_turco
Pooh-Bah
Reged: 08/29/09
Loc: Lincoln, RI
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: MKV]
#5537102 - 11/24/12 11:40 AM
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May I say something a little off topic? Robert Lurie in his 1976 paper proposed a system with a full lens corrector (Asymmetrical in form and two BK7 elements in contact) with a hyperbolic mirror; it was a dandy. I know that the term "Too much glass" is bandied about but the system was not only coma corrected, but anastigmatic, meaning no astig either. I wish I had built it. Mike, any comments? I think I might have the numbers somewhere...
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Loc: Fort Worth TX
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: ed_turco]
#5537527 - 11/24/12 04:56 PM
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Hi Ed,
We're still out on the road for holidays. If you'll post up Lurie's prescription, we can give it a look in ZEMAX and OSLO.
Mike
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kfrederick
Carpal Tunnel
Reged: 02/01/08
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: Mike I. Jones]
#5537608 - 11/24/12 05:54 PM
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Mike how big can this design go ? Thanks
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MKV
Carpal Tunnel
Reged: 01/20/11
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: ed_turco]
#5537852 - 11/24/12 09:09 PM
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Ed, Mike: Lurie's 1975 work gave G-sum equations for a corrector to be used in conjunction with a parabolic (not hyperbolic) mirror. It was intended to serve as a means of converting ordinary Newtonians into anastigmatic cameras. But his principle can be applied to an entire family of conic mirrors, not just paraboloids.
I discussed his design and one special case he intended for amateurs (using an ellipisoidal mirror and a plano-convex, plano-concave corrector) in The Best of Amateur Telescope Making Journal, Volume 2, 17-18.6 "Lurie Anastigmats", pp. 375-392, Willmann-Bell, 2003.
I have his 1975 JOSA article and will gladly post the equations - unless Mike thinks it's off topic.
Mladen
Edited by MKV (11/25/12 12:59 PM)
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wh48gs
Pooh-Bah
Reged: 03/02/07
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: Loren Chang]
#5538700 - 11/25/12 12:53 PM Attachment (20 downloads)
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Loren,
That's interesting arrangement, positive element in front. still only four glass-to-air surfaces. When scaled up to 250mm f/3.5 it is not quite as good as Mike's color-wise, but that wouldn't cause any difference in practical terms. But why use FPL51, if FPL53 is (I think) cheaper? Here's what it looks like.
Vla
Edited by wh48gs (11/25/12 01:28 PM)
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cjc
sage
Reged: 10/15/10
Loc: Derbyshire, England
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: MKV]
#5539779 - 11/26/12 03:25 AM
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Quote:
...
Speaking of tinkering on those cloudy nights, it would be interesting to do a direct theoretical comparison of this Mike I. Jones-Rosin corrected system as opposed to a 10-inch f/3.5 Newtonian with a Paracorr and a 10-inch f/3.5 Newotnian using a Wynne-type corrector (both of which are commercially available).
...
Mladen
These are not quite what you want, but there is a coma corrector design with two cemented doublets in the Telescopes, Eyepieces, and Astrographs by Smith, Ceragioli and Berry. Orion Optics have spots for a set of F3.8 Newtonians with an Optimised Wynne corrector with the 10" spots here:
http://www.orionoptics.co.uk/AG/ag10spots.html
and the others being accessible from here (follow the red links in the table):
http://www.orionoptics.co.uk/AG/agrangeand%28ota%29t.html
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MKV
Carpal Tunnel
Reged: 01/20/11
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Re: 10" f/3.5 Astrograph with Rosin focal reducer
[Re: cjc]
#5539823 - 11/26/12 05:34 AM
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Thanks cjc. Interesting "hybrid" corrector. Bear in mind that the Rosin works only with a hyperbolic mirror, which means the corrector must be used all the time, whether observing visually or photographically. The others, the Ross, Wynne, Paracorr, and the Orion's version work on your ordinary Newtonians with parabolic mirrors which can be used with or without the corrector. Of course, if you have an f/3.5 Newotnian you'd be using the corrector all the time! 
The design and the results of all of these are either public knowledge or can be obtained by raytracing, but not of Paracorr. My understanding is that it consists of two cemented achroamts. It would be interesting to see how Paracorr would compare in an f/3.5 Newtonian, one degree off-axis, against the other correctors.
Mladen
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