Re: [ATM] Rebuilding the mirrorcell

[Jeff Anderson-Lee <jonah@eecs.berkeley.edu>]

Treur, Harro wrote:

>Hello all,
>
>I am rebuilding the lightweight Dobson I built in 1993 (12,5 inch, f 4,8
>Thickness of primary = 2,00 inch, made by Galaxy Optics).
>I have problems with the collimation, probably because of the mirrorcell. 
>At this moment the mirrorcell is 9 point and is a crude version of the
>Kriege design.
> 
>I have not used PLOP yet, but after following the ATM-forum for some months,
>I expect that 9 points is far more than necessary. (I understand that a 16
>inch of 1,5 thickness can be placed on a 6-point, though properly built).
>
>Question 1: What do I need for my new mirrorcell?  6-point? 3-point? 
>Question 2: are there any good examples described in words and images on the
>net? 
>Question 3: I once read that someone advised to place a mirror on plastic
>Bubble-foil (not only for Figuring, but also for mirrorcell. I remember this
>was a person form Scotland). What do you think of that?
>
1) Three points should be adequate for that mirror.  You could certainly 
try that first.  Support radius of between 0.413R to 0.470R.  That's 
2.58 to 2.94 inches (65.5 to 74.6 mm).

3) I'd not suggest that for viewing, as the bubble wrap would interfere 
with the mirror cooling down and might not be steady enough to avoid 
changes in collimation.  However if you don't have much day/night 
temperature change where you are you could try it simply enough.  
Likewise for shag carpet and astroturf.

Jeff Anderson-Lee
Sacramento, CA, USA



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