Click here if you are having trouble logging into the forums
Privacy Policy |
Please read our Terms
of Service | Signup and
Troubleshooting FAQ | Problems? PM a Red or a Green Gu.... uh, User
Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
|
|
... 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.
--------------------
Ed Jones
|
kfrederick
professor emeritus
Reged: 02/01/08
Posts: 666
|
|
EDS YAHOO GROUP IS SPIDERLESS
|
Brian Engel
member
Reged: 08/25/09
Posts: 93
Loc: Cincinnati,Oh
|
|
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?
|
timo4352
super member
Reged: 04/16/07
Posts: 160
Loc: Northeast Ohio
|
|
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
--------------------
Orion 3.6CA Reflector
and 2 homebrew scopes --
8" Hubble Bubble ballscope
8" F/8 CHief - nearing completion 
|
Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
|
|
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.
--------------------
Ed Jones
|
RossSackett
professor emeritus
Reged: 08/17/07
Posts: 692
Loc: Memphis, TN
|
|
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
--------------------
"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
|
kfrederick
professor emeritus
Reged: 02/01/08
Posts: 666
|
|
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
|
skyward_eyes
Carpal Tunnel
Reged: 12/12/06
Posts: 2102
Loc: Arizona
|
|
APM is finishing up a 20" Apo. so there are fairly large Apos out there.
|
Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
|
|
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.
--------------------
Ed Jones
|
RossSackett
professor emeritus
Reged: 08/17/07
Posts: 692
Loc: Memphis, TN
|
|
Thanks, Ed.
--------------------
"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
|
kfrederick
professor emeritus
Reged: 02/01/08
Posts: 666
|
|
ED LOOKS LIKE THE EYEPIECE IS 52 INCHES ABOVE THE PRIMARY !!NO LADDER
|
mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2159
Loc: salem, OR
|
|
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
|
Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
|
|
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
|
Mark Harry
Post Laureate
Reged: 09/05/05
Posts: 3125
Loc: Northeast
|
|
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.
--------------------
So many projects, so little time!
|
Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
|
|
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.
--------------------
Ed Jones
|
Mark Harry
Post Laureate
Reged: 09/05/05
Posts: 3125
Loc: Northeast
|
|
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
--------------------
So many projects, so little time!
|
Mark Harry
Post Laureate
Reged: 09/05/05
Posts: 3125
Loc: Northeast
|
|
If you are looking for something to occupy time-
You could regrind that puppy..... (a nice winter project!)
Go for it!
M.
--------------------
So many projects, so little time!
|
Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1415
Loc: Sin-sin-atti
|
|
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.
--------------------
Ed Jones
|
Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
|
|
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
--------------------
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.
|
mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2159
Loc: salem, OR
|
|
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
|
|
13 registered and 4 anonymous users are browsing this forum.
Moderator: Don W, Mike I. Jones
Print Thread
|
Forum Permissions
You cannot start new topics
You cannot reply to topics
HTML is disabled
UBBCode is enabled
|
Thread views: 1376
|
|
|
|
|
|
|
Previous
Index
Next
Threaded
Edit
Reply
Quote
[Re: 