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12" Dob, How light before instability?



 
 
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  #1  
Old December 22nd 05, 01:22 AM posted to sci.astro.amateur
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Default 12" Dob, How light before instability?

Assuming you used the very best materials and design
available, how light could you make a field-assembleable 12"
Dob before it simply would not stable enough in operation or
have the ability to hold collimation? I've used/owned pretty
much every commercial scope going, but I've not used
Newtonians very much.
-Rich
  #2  
Old December 22nd 05, 02:00 AM posted to sci.astro.amateur
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Default 12" Dob, How light before instability?

Gary Wolanski built a 15" F5 dob that, including the mirror, weighs a
total of 40 pounds!

I've looked through it and it is superb!

Wayne Howell
Photon Phlats Observatory
Port Townsend, WA

Rich wrote:
Assuming you used the very best materials and design
available, how light could you make a field-assembleable 12"
Dob before it simply would not stable enough in operation or
have the ability to hold collimation? I've used/owned pretty
much every commercial scope going, but I've not used
Newtonians very much.
-Rich

  #3  
Old December 22nd 05, 04:09 AM posted to sci.astro.amateur
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Default 12" Dob, How light before instability?

Wayne Howell wrote:
Gary Wolanski built a 15" F5 dob that, including the mirror, weighs a
total of 40 pounds!

I've looked through it and it is superb!


My brother-in-law was telling me today about a 12.5 lb road bicycle he
saw. Lots of carbon fiber and Ti. I figure if a bike can be made this
light, the structure of a scope could easily, albeit expensively (the
bike was $8k) be made this light and probably a lot lighter. If you got
the big bucks talk to these guys: www.hextek.com for a mirror, or
http://www.rfroyce.com/conical/ 14 lbs for a 12.5" conical mirror that
won't be as expensive as honeycomb. Add 16 lbs of structure and you
have a 30 lb scope.
Here's an applicable site:
http://www.tms-usa.com/grayarea/janes16/jane16.htm


Shawn
  #4  
Old December 22nd 05, 05:30 AM posted to sci.astro.amateur
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Default 12" Dob, How light before instability?

Stability is a function of design and good engineering and has little
to do with mass. Wide stance, low center of gravity, rigid structure
are the objectives of good design, and light weight!


Steve
Oregon

On Wed, 21 Dec 2005 19:22:41 -0500, Rich wrote:

Assuming you used the very best materials and design
available, how light could you make a field-assembleable 12"
Dob before it simply would not stable enough in operation or
have the ability to hold collimation? I've used/owned pretty
much every commercial scope going, but I've not used
Newtonians very much.
-Rich


  #5  
Old December 22nd 05, 11:14 AM posted to sci.astro.amateur
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Default 12" Dob, How light before instability?

Rich writes:

Assuming you used the very best materials and design
available, how light could you make a field-assembleable 12"
Dob before it simply would not stable enough in operation or
have the ability to hold collimation?


I rebuilt my 10" Dobsonian to cut weight and got down to 9kg
(including finder scope and a full tichness primary mirror at about
5kg). That is without mount, as the whole point was to put it on my
Vixen GP-DX equatorial mount for CCD imaging. I used wood and steel
(but sparingly) so there is room for further weight reduction with
more exotic material. However, although it does work for the intended
purpose, is a borderline construction and I usually prefer my more
compact 6" MAK.

pej
--
Per Erik Jorde
 




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