Re: [ATM] Telescope Mounts

[Mark Holm <mdholm@telerama.com>]

I don't think I would say that German equatorials are unstable.  If 
built poorly, they may be more subject to vibration and flexure.  They 
do require more stiffness at certain points in the structure to resist 
vibration and flexure.  The polar axle to fork joint is about the same 
as the polar axle to dec bearing housing as far as stiffness 
requirements.  Actually, the fork may be worse because the cg of the 
scope is farther from that joint.

Pier interference is a problem with Germans.

Some 1960's vintage Boler & Chivens (later Perkin-Elmer) scopes got 
around the problem of pier interference with a greatly extended polar 
axle.  This of course would make stiffness a problem.  They dealt with 
it by making the polar axle extension a very large diameter tube and 
mating it to a very large diameter bearing at the top end of the polar 
axle proper.  I suspect the polar axle proper was also rather large.  
These scopes sold fairly well to professional astronomers, so one 
suspects the design couldn't have been too bothered by flex or vibration.

In the early 70's, somebody advertized a fairly large scope on a one 
tine fork.  Similar in concept to the Boler & Chivens, except the 
counterweight was avoided by bending the polar axle extension to center 
the cg on the polar axis.  This is also essentially a deformed German mount.

Mark Holm
mdholm@telerama.com
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