Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
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... no ladder, no expensive glass, no huge GEM..
There are a lot of possible variants to the Chief and here's one that's particularly interesting. In this one the secondary is a very slightly curved hyperbolic (conic is -720) changinging the f# from 10 to 12. This corrects the image tilt and with a hyperbolic primary eliminates coma. Not sure if I'll ever make one with all my other projects but it's fun to compare it to a 16 inch APO,.. uh OK so there aren't any 16 inch APOs.
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Ed Jones
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kfrederick
professor emeritus
Reged: 02/01/08
Posts: 669
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EDS YAHOO GROUP IS SPIDERLESS
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Brian Engel
member
Reged: 08/25/09
Posts: 93
Loc: Cincinnati,Oh
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I have a probably dumb question....
A friend of mine experimented with making off axis parabolids several years back. The idea is the primary mirror instead of being tilted had a curve generated into it that the mirror would be flat but focus light off the incoming axis of light.
Just wondering how/if this would work into a Chief design? Simplier? Complex? Not plausable?
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timo4352
super member
Reged: 04/16/07
Posts: 160
Loc: Northeast Ohio
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Hey Ed
If the secondary corrects for the tilt then what purpose do the lenses serve now? Color?
What kind of eyepiece height do you figure with this one?
You paying attention, Kevin? -- You've got a piece of glass coming, don't you?
Tim
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Orion 3.6CA Reflector
and 2 homebrew scopes --
8" Hubble Bubble ballscope
8" F/8 CHief - nearing completion 
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Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
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Brian,
There is no advantage to using an off axis primary in the Chief and making off axis mirror is more expensive than a symmetrical primary.
Tim,
The secondary corrects the image tilt, the lenses correct the tilt aberrations of the tilted primary.
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Ed Jones
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RossSackett
professor emeritus
Reged: 08/17/07
Posts: 692
Loc: Memphis, TN
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The FILE, Ed....We need the file on that one. 
I think I know how I would mount that on a single pole. Getting those large correctors will be an issue, but that looks like a very practical telescope to me.
Ross
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"A craftsman relies on science when the state of knowledge allows it, tradition and experience when it does not, and makes art whenever he can."
12 scopes from 4.25 to 18" and a 24" in progress. 12 ATM awards. Webpage: http://stardazed.com/ Some more scope pix at http://www.flickr.com/photos/8315630@N04/
Anagrams: Amateur astronomer = A mature moon-starer; Dobsonian maker = Debonair as monk
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kfrederick
professor emeritus
Reged: 02/01/08
Posts: 669
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Tim yes I ordered a 16 inch blank pregen f 10 . i have a tool with 320 rc /BY the time i get the primary done ,ED will have invented something even better .EDs telescopes work..great//kevin fredeick
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skyward_eyes
Carpal Tunnel
Reged: 12/12/06
Posts: 2105
Loc: Arizona
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APM is finishing up a 20" Apo. so there are fairly large Apos out there.
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Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
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Ross,
Here is the design. Correctors are about 4 inches and would have to be made. Yo would need to make a test plate for the secondary too.
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Ed Jones
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RossSackett
professor emeritus
Reged: 08/17/07
Posts: 692
Loc: Memphis, TN
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Thanks, Ed.
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"A craftsman relies on science when the state of knowledge allows it, tradition and experience when it does not, and makes art whenever he can."
12 scopes from 4.25 to 18" and a 24" in progress. 12 ATM awards. Webpage: http://stardazed.com/ Some more scope pix at http://www.flickr.com/photos/8315630@N04/
Anagrams: Amateur astronomer = A mature moon-starer; Dobsonian maker = Debonair as monk
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kfrederick
professor emeritus
Reged: 02/01/08
Posts: 669
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ED LOOKS LIKE THE EYEPIECE IS 52 INCHES ABOVE THE PRIMARY !!NO LADDER
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2159
Loc: salem, OR
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Hi Ed,
This is interesting - the conic on the primary should be easy enough considering the f/ratio is f/10, but the secondary is an f/53 with -720 conic? Any feeling for how hard that is (you mention a test plate but it's concave)? What about FOV?
Best,
Mark
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Another good one, Cuz! I have a 16" f/6 Newtonian with a beautifully corrected primary I would love to convert to your unobstructed Chief layout, but that's just too fast a primary to tilt that far.
Mike
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Mark Harry
Post Laureate
Reged: 09/05/05
Posts: 3128
Loc: Northeast
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I have tooling for an 8" F/10, a 6" F/25 that I could use for a secondary testplate..... All I'd need to do, is hunt up a couple lenses for this one! I could have an 8" version fairly easily, hmmm.
Those tiny spotplots look mighty interesting! Way to go, Ed!
M.
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So many projects, so little time!
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Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
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Mark,
If I were to make this secondary I would use a glass tool and polish both using an accurate spherometer (sag is only 0.24 mm) You could check it by focusing on the sun. By decentering one against the other you can work any errors in both so that they are a good spherical match. Then I would aspherize the secondary using the test plate to give the right fringe profile, the deviation is only about a fringe so it's not as bad as you might think.
The field of view, these plots are +/- 1/4 degree. You could go larger with larger lenses and secondary. At 1/2 degree off axis the spot are about 3 times the airy disk.
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Ed Jones
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Mark Harry
Post Laureate
Reged: 09/05/05
Posts: 3128
Loc: Northeast
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I made a concave 6" F/25 with a shorter radius polisher backer,(~112", with used #73 pitch) and the conic came out of polishing roughly -120 for the conic. So making a testplate for that secondary wouldn't be too difficult. You could look for just straight lines if the right deformation was on the testplate.
I'd like to know how close to the final deformation that would be needed to work fairly closely to what your plots show above. is -600 to -800 close enough?
Mark
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So many projects, so little time!
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Mark Harry
Post Laureate
Reged: 09/05/05
Posts: 3128
Loc: Northeast
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If you are looking for something to occupy time-
You could regrind that puppy..... (a nice winter project!)
Go for it!
M.
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So many projects, so little time!
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Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
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Mark,
You would be working to a fringe profile with a test plate and you would want to match that profile as accurately as you could. I could print out a table for you in Zemax.
Also I didn't have my font set right and the primary conic is 1.639. Here it is corrected.
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Ed Jones
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Nuh uh, I ain't regrinding a 1/18 wave RMS 16-incher! I do have another 16" blank I could do, though. But I have a 10" f/26 Mak ahead of it!
Miguel
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56 mirrors, lenses, 16" f/6 Newt, 6" f/10 refractor, TOA-130S, Tinsley 5" f/15 Mak, 6" f/4 RFT, Coronado PST. Still to build: 24" f/10 Modified Dall-Kirkham, 10" f/26 Mak, 8" f/12 apo, spectrohelioscope, Herrig, Schupmann, and others.
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2159
Loc: salem, OR
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Ed,
Can the design be applied to shorter f/ratios with the addition of the two new elements shown here (hyperboloidal primary and secondary), perhaps with some of the more exotic glasses in the correctors, since these are custom anyway? Again I'm thinking about competing with largish APOs and kicking their butts. 
Best,
Mark
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Ed, that's a great f/12 design. I keyed your prescrip in and got the layout and ZEMAX full-field spot plot shown, with Airy ring indicated at center. The outer circle is plotted exactly 2" in diameter, but the spots and Airy ring are plotted 200X larger than they really are. Very good performance over the field.
Mike
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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HOWEVER, going tilted and unobstructed for my 16" f/6 primary doesn't come out "quite" so good (like nowhere near). This first design uses a long-radius conic secondary similar to Ed's, and N-LLF6/N-BK10 correctors. The spots are huge.
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Tried something a little unusual - an all-spherical wedged Mangin mirror. The refractive front and reflective rear surfaces are tilted to each other by 1.67 deg., the thicker side below. The Mangin is Ohara S-FPL51, and the correctors are Ohara S-TIM22 and Schott N-LaK21. That did help get the spots down smaller as you can see, especially the on-axis spot. But still a long way from Ed's nice pointy images over the FOV.
I'm going to continue to mess with it - I love the idea of no central obstruction, but the imagery without it has to be of high enough quality to be worth the trouble to build, which these designs are not. A 16" f/6 is just a really hard mirror to make unobstructed.
Mike
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kfrederick
professor emeritus
Reged: 02/01/08
Posts: 669
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ED how much better is this than if you used a flat . THANKS for all the cool telescopes .
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Mark Harry
Post Laureate
Reged: 09/05/05
Posts: 3128
Loc: Northeast
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"This corrects the image tilt and with a hyperbolic primary eliminates coma. "
********************
Have been thinking about the secondary, and these aspects. If it corrected for the image tilt, there wouldn't need to be a pair of lenses, correct?
The hyperboloidal mirrors correct for just coma, like an RC "on axis" scope???
Just trying to let my mind grasp all the aspects of this design.....
==========================================
I've got a "what if" idea. The primary is about F/6. Let the light come to focus, and allow the secondary to be concave, located maybe 120-130" away from the primary, with a fairly low primary tilt. The secondary tilt bounces the light to the side below the primary, with a pair of lenses to cancel out the tilt abberations. (something like an off axis Gregorian)
Something tells me that the image tilt could be messed up, but perhaps it might be worth looking at???? 
Mark
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So many projects, so little time!
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Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
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I tried to make it faster to answer Marks question, I think it is still OK at f/9.8. At f/8.2 the spots at .25 deg off axis are a half again larger than the airy disk size. That's with a f/7.1 primary. It's hard to go much faster because of the secondary amplification. Using more exotic glass in the correctors can improve the spots a bit but fused quartz lenses is nearly as effective and probably a lot less expensive. I used it in these faster designs.
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Ed Jones
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kfrederick
professor emeritus
Reged: 02/01/08
Posts: 669
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why is mark and mark trying to have ED CHANGE THE PERFECT TELESCOPE HOW MUCH MORE DO WE NEED . LETS GET BUILDING AND GO WITH IT AS IS.. MIKE JONES SAYS IT IS VERY GOOD . THAT IS GOOD ENOUGH FOR ME .THANKS ED
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kfrederick
professor emeritus
Reged: 02/01/08
Posts: 669
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I know they wonder about doing it different ways . i have ask Ed hours of question and in the end his way is the way to go .. he has it all figured out.just build it buy the numbers! not much diferent than a newtonian! . a f10 mirror is harder than a f5 but not much more .not sure on the secondary
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Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
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There is not a lot of coma in an f/10 Chief especially compared to a faster Dob. You'ld have to weigh the benefits in performance to the extra work of making the hyperbolic secondary versus the regular Chief.
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Ed Jones
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2159
Loc: salem, OR
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Kevin,  Change the perfect telescope?? There is no perfect telescope! Ah, except the one you own, of course.
What I'm curious about (ever since Ed mentioned the shorter design work) is where the design could go for production optics, that's all. Wider fields, shorter OTAs, "exotic" elements all have appeal commercially. Nobody says anybody has to deviate from what they like, I'm just a curious sort. Like what Mark H. says:
Quote:
Just trying to let my mind grasp all the aspects of this design.....
Ed, transmission quartz at .8" thick is available (by picking it out from blanks) in small quantities to 14.7" diam, is this adequate? Around f/8 on the 16"? What about smaller, down in the 8-10" size? IIRC it scales faster smaller, or is that just my averted imagination??
Best,
Mark
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Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
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That quartz is plenty big enough, the lenses are only about 4 inches and thickness isn't very important. Primary is f/8.4. Here's the design.
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Ed Jones
Edited by Ed Jones (11/04/09 07:01 PM)
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kfrederick
professor emeritus
Reged: 02/01/08
Posts: 669
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MARK I KNOW I ASK ED THINGS ALL THE TIME .ALOT OF WAYS TO BUILD A CHIEF ..ED CAN MAKE A OFFAXIS WORK UP TO 50 INCHES .PRICE OF A 16 INCH PYREX 1 5/8 INCHES THICK PREGENTERATED BLANK IS 625 . DOLLARS.
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kfrederick
professor emeritus
Reged: 02/01/08
Posts: 669
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hi MARK C YOU COULD GET A TEST PLATE/ SECONDARY MIRROR/ AND TWO LENS OUT OF ONE 14.7 INCH QUARTZ BLANK.. I THINK.. ALL QUARTZ OPTICS. MAYBE A 14.7 INCH PRIMARY
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2159
Loc: salem, OR
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Thanks, I think you're right. Some of the plates have no bubbles and are refractive grade, most of them have bubbles and aren't refractive grade. I've tested a few that could make lenses and I can get some more. I like the all-quartz approach.
Best,
Mark
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kfrederick
professor emeritus
Reged: 02/01/08
Posts: 669
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yes that sounds great[QUARTZ OPTICS]. great optical design. great optics . a ultralight mount!! sounds like a goode
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Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
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Forgot to change the glass type from BK7 to silica on that last design. It is fused quartz not BK7 (I must have CRS). 
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Ed Jones
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kfrederick
professor emeritus
Reged: 02/01/08
Posts: 669
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CRS??
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Can't Remember "Stuff" (ya have to say "stuff" to not violate TOS and get bleeped) 
Mike
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kfrederick
professor emeritus
Reged: 02/01/08
Posts: 669
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I THOUGHT MAYBE CHIEF REFLECTOR SICKNESS
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marcething
member
Reged: 04/20/06
Posts: 19
Loc: Lint , Belgium , Europe
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Hi Ed ,
Is the CHiefspiegler with no CA, no coma, no image tilt, no obstruction,no Sherical aberartion ... possible at F/8 for a 10 or 12" , and could you please calculate this ?
Thanks in advance
Marc
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Mark Harry
Post Laureate
Reged: 09/05/05
Posts: 3128
Loc: Northeast
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Scale it smaller, but adjust your image plane diameter to match your particular format. Generally, you won't have issues in going smaller. (multiply any ROCs and spacings by 3/4, or 5/8)
Mark
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So many projects, so little time!
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kfrederick
professor emeritus
Reged: 02/01/08
Posts: 669
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I am polishing a 16 inch f 10 mirror for a CHief . WE were spliting stars with my 20inch chief last two nights .
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Kobayashi
sage
Reged: 07/10/08
Posts: 381
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Quote:
A friend of mine experimented with making off axis parabolids ... Just wondering how/if this would work into a Chief design? Simplier? Complex? Not plausable?
The whole idea of a Chief* is to make an obstruction-free reflective telescope without the need for expensive off-axis optical elements. Symmetric mirrors are always much easier to make than off-axis mirrors. In fact, off-axis mirrors are usually made by making a large symmetric "parent" mirror and cutting pieces out of it.
But if you must have an unobstructed telescope and money is no object, I think using an off-axis primary mirror is more desirable. An off-axis parabola alone acts as a pretty decent 1-mirror telescope (sort of an improved Herschelian), or you can add a fold mirror and call it an off-axis Newtonian. If coma is a problem, there are ways to correct for that.
*I'm assuming this is an Anglicization of the term "Schiefspiegler", is that correct?
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-- Ken Kobayashi
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Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
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Quote:
*I'm assuming this is an Anglicization of the term "Schiefspiegler", is that correct?
No it is my name for "Catadioptric Herschelian schiefspiegler", a design I invented.
In addition to being quite expensive an off-axis Newt has a portion of the faster primarys coma. I guess you could fix it with a Paracorr but that would be problematic too getting it aligned correctly. You run the risk of a figure change in cutting out an off axis mirror BTW.
You can always scale down a design but you can't speed it up. Here's an f/8 version in a 12 inch size.
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Ed Jones
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kfrederick
professor emeritus
Reged: 02/01/08
Posts: 669
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IS THAT THE ALL QUARTZ CHIEF ? MARK C LIKES THE SOUND OF THAT.
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Kobayashi
sage
Reged: 07/10/08
Posts: 381
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Quote:
No it is my name for "Catadioptric Herschelian schiefspiegler", a design I invented.
Sorry for my misunderstanding, and thanks for the correction.
(I did understand it's your own design, as it is different from the more "traditional" Schiefspiegler designs.)
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-- Ken Kobayashi
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marcething
member
Reged: 04/20/06
Posts: 19
Loc: Lint , Belgium , Europe
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Super , Thanks Ed 
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Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
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Yes silica is the same as fused quartz. 
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Ed Jones
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marcething
member
Reged: 04/20/06
Posts: 19
Loc: Lint , Belgium , Europe
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Hi Ed
One more question :
I have a rather litle obesevatorium / roll-off roof shed (6x6) . the distance between primary and secundary is in the F/8 a rather snap fit
Would it be possible to make it a 12" F/7 or is that to fast to keep it compliant to : no CA, no coma, no image tilt, no obstruction,no Sherical aberartion ...
Can you also put the Zemax or Oslo file either here or on the Spiderless yahoo group please
Thanks a lot in advance
Marc
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Mark Harry
Post Laureate
Reged: 09/05/05
Posts: 3128
Loc: Northeast
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Now lets see, the sag on that convex secondary is .005166", and the longitudinal delta would be 10.6" on a fixed source tester for making a concave test plate..... Gotta be an easier way to make that thing.
Probably a spherical secondary with an elliptical primary would not have anywhere near the tight plots. But how would a spherical secondary/elliptical primary combination compare with an F/8 Newt? I never heard much complaint about an F/8 Newt.....?
(Just thinking out loud.)
Mark
Mark
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So many projects, so little time!
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kfrederick
professor emeritus
Reged: 02/01/08
Posts: 669
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There is very little coma in a 16 inch f 10 NEWT/ The chief has the same amount of coma. i am using a flat. i think .Better ask ed
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Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
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Marc,
No I/m not very happy with the peformance when you get under F/8. What I can do is shorten up the primary - secondary separation by 5.5 inches. This tilts the primary 4.0 deg. and isn't quite as good as above. If this will work for you then I'll post it on spiderless.
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Ed Jones
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marcething
member
Reged: 04/20/06
Posts: 19
Loc: Lint , Belgium , Europe
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That would be perfect Ed
Thanks a lot in advance
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marcething
member
Reged: 04/20/06
Posts: 19
Loc: Lint , Belgium , Europe
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Could you post them both please Ed , The original 12"F/8 ( the Oslo or Zemax file ) and the one with the shorter primary to secundary distance ?
Thanks a lot in advance
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marcething
member
Reged: 04/20/06
Posts: 19
Loc: Lint , Belgium , Europe
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Hi Ed ,
the file : 3451150-12inchf8 aplanat.jpg you added on 16 nov , is an extract of what program ? Zemax ?
Thanks in advance
Marc
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Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
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Yes it is from Zemax, that's what I use. Also I uploaded a Zemax file for this shortened version of the 12 inch F/8 Chief in spiderless for you.
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Ed Jones
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marcething
member
Reged: 04/20/06
Posts: 19
Loc: Lint , Belgium , Europe
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Oops ,I thought that I was going to be able to open the Zemax file with the demo version , like in Oslo ....
 Not
Ed , could you please convert the design to a jpeg , as the 3451150-12inchf8 aplanat.jpg ?
Thanks in advance
Marc
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marcething
member
Reged: 04/20/06
Posts: 19
Loc: Lint , Belgium , Europe
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Thanks Ed .
1 litle remark : shouldn't the diameter in the table for surface 1 be 12" ?
Mark
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