Re: ATM A cage as secondary holder

[ran@netgate.net]

In <199807210159.TAA13795@intergate.pvtnetworks.net>, on 07/20/98 
   at 07:59 PM, iss@pvtnetworks.net said:


>Re the (re)movable secondary cages, one of the problems with building
>accurate telescopes/mounts (in terms of tracking and finding things) in
>amateur class systems is the need to have the telescope axes orthogonal
>(ra/dec or alt/az), and have the optical axis also orthogonal to the
>alt/dec axis. It's
>not that hard to build the mount accurately and, once built
>and aligned, it usually stays that way.

I would guess that "usually" it doesn't:  i.e.,  that most mounts get
moved frequently as they're hauled from observing site to site,  and back
home to be "parked" between sessions.

The axes will stayed aligned *with each other*,  but not with the rest of
the universe.  So any control system needs provisions to compensate for
that.  And the compensation factors need to be recalculated every time the
mount is set up.

Meanwhile,  unless you can rotate the tube (which is common,  I know), the
error added by collimation movements is constant (for the observing
session),  and can be compensated for by the same system that handles
errors in polar alignment.  If you do rotate the tube,  a fairly quick
recalibration should cancel out the new error constant.

Ran


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