Re: [ATM] considering different design

[mdholm@telerama.com]

>This is not intuitive.  I can see how the support must be  stronger to create 
>the same solid working.  I'm not questioning the  accuracy, but I don't 
>understand why a higher balance point should affect a  solid smooth working. 
>Can you explain?


Generally, the lower the center of gravity of the optic tube, the shorter the
mount can be.  This may mean the pier of a german mount or the forks of a
Dobsonian or equatorial fork.  The shorter the structural members of a mount,
the more inherently stiff they are.  You can make up for it with bigger cross
section structural members, but, all else being equal, shorter structural
members are better.

Mounts that are not stiff enough are a real problem, especially at high power.

Lots of people not familiar with basic structural design confuse strength and
stiffness.  It isn't terribly hard to make an amateur telescope strong enough
that it won't break in ordinary use.  It is not always so easy to make one stiff
enough.

Kriege and Berry, "The Dobsonian Telescope"  has a discussion of stiffness as it
applies to the style of scope they are discussing.  The general principles they
describe apply to all structures.

Mark Holm
mdholm@telerama.com
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