Re: [ATM] Fw: 20" telescope

[James P Crombie <jpcrombie@pei.eastlink.ca>]

David
  Go get NEWT telescope program and you can play with the variables to 
get the best reuslts
http://home.att.net/~dale.keller/atm/newtonians/newtsoft/newtsoft.htm
  I would locate the mirror cell as far back as possible but still leave 
enough room for some way to reinforce the tubing around the end.  Such 
as a rings of plywood or fibreglas.   Most of the tubes I have seen are 
much thicker for this dia.
  I take it that this will not be a portable scope :-)   I helped move a 
17 1/2 coulter for a friend and that was tough :-)


David Williams wrote:

>
>
>Hello ATM list
>
>I am still building the 20" telescope (that's the mirror's external diameter, but the sonotube is 24" outside diameter:)  and I was wondering what kind of secondary mirror to use for that purpose.  I will use a 3.1 inch minor dimension axis secondary, but does anyone know what kind of percentage or blockage of the primary each would be, and the difference in contrast?  
>
>Of course the bigger the mirror the bigger the price and so I'm looking for the smallest price and there fore hope to find a happy compromise between the cost and the performance.  
>
>
>PS 
>
>My tube is 8 feet and 3 inches long and 24 inches wide (1/4 inch thick) and the mirror is 1 inch thick, 20" diameter, focal length 100 inches, and the mirror cell is 4 to 5 inches thick from front to back.  Where should I locate the mirror cell (rear edge) from the back of the tube and where should I put the spider with the secondary mirror and the eyepiece focuser too?
>
>Thank you.
>David Williams
>Bye
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