Re: [ATM] secondary size dillemma

["Alan Scott" <alanne1956@hotmail.com>]

Tim,
  newt says that you are OK, but on the edge.  I would try the 2.6", and 
would guess that you will be fine.  Center brightness is what is most 
important, anyway.

alan
http://www.xmission.com/~alanne/DS3Main.html


>From: "Tim Nott" <timothy.nott@ims.sa.edu.au>
>To: <ATM@atmlist.net>
>Subject: [ATM] secondary size dillemma
>Date: Wed, 16 Nov 2005 19:27:16 +1030
>
>Help!
>
>As a first time telescope builder I have about 3/4 finished my tri-dob 16 
>incher.  My dillemma is to do with my secondary size.  I have already 
>bought &designed my f4.9 scope with a 2.6'' secondary holder, an ultra low 
>profile focuser, then moved it up a bit to allow me to add a focuser 
>baffle.  However, when I now run the figures through Andy's program I end 
>up with a 71% edge of field illumination (for the widest field eyepiece I 
>intend to use - 26mm nagler giving 1 degree field) but only a 0.01 degree 
>or a 0.21mm 100%illuminated field of view with a16% central obstruction. 
>Will this be a significant problem if I am only using the scope for visual 
>use?
>
>If I was to go up to a 3.1'' secondary the figures would be 85.68% edge of 
>field illumination, 0.44 degree or 15.37mm 100%illuminated field, and a 19% 
>central obstruction. Should I bite the bullet & order a 3.1'' secondary and 
>if so does anyone think it might be possible to silicone the mirror to the 
>outside of the 2.6'' novak sleeve-style holder or should I buy a 3.1'' 
>secondary holder as well.
>
>Tim Nott (Australia)
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