ATM Re: atm-digest V1 #2240

["Art DeBrito" <ionheavens@hotmail.com>]

The only problem I see with big bearings that are offset, as illustrated 
below, is that the optical axis varies as the altitude is adjusted. That 
would eliminate the accurate use of a poncet platform.

-art-

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Date: Wed, 09 Aug 2000 07:27:49 -0700
From: John Price <jmprice@cbvcp.com>
Subject: Re: ATM REALLY BIG elevation bearings for 6 inch Dob ?

Jim,

Jack Day took a picture of my 10" f/6 scope at Table Mountain Star
Party. -- I was playing around with really big bearings (-22" in dia.)
to see how they'd work. Rather than using solid circles, I use 3" thick
arcs. I really like them.

On the plus side:

    Very smooth  motion.
    Allows me to have the balance point above my mirror box and not have
to use counter weights.
    Keeps the profile lower and mirror box smaller. (I can easily fit
the scope and camping gear into my Honda.)
    Pretty.

On the minus side.

    I have to take the bearings off when I pack up the scope because
assembled, it wont fit in my small trunk.
    I need to modify the design slightly to improve the stability at low
elevations. This will involve a support across the top of the arc to
reduce the "bounciness" I see near the horizon at high mag, when the
whole weight of the scope is resting on the ends of the arc. Once I
solve this problem, I'd call the experiment a big success.

John Price

Jack's picture is at:
http://www.stargazing.net/aaa/t2k/10inchwire.jpg










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