Re: ATM A cage as secondary holder

[iss@pvtnetworks.net]

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. This is not the case
with the typical Newtonian that rides on this mount. All the
optical elements are made adjustable in several degrees of
freedom for optical collimation, this means that the final
optical axis may end up not being orthogonal to the alt/dec
axis after collimation tweaking. Getting the OA perpendicular
to dec/alt is not a trivial exercise to begin with so I've
been thinking of ways to do collimation that disturbs the
OA the least possible amount. One way to do this is to
collimate the primary/secondary initially and then do the OA
orthogonality calibration. Any subsequent collimation would
be done by moving the entire secondary cage normal to the 
axis of the primary (rather than tilting the primary). If
the primary mounting is sufficiently rigid the collimation
tweaking should result in the OA being returned to its original
location.

This is probably not a concern for systems built for visual
only observing, but tracking/pointing for CCD/photo imaging 
is another animal entirely.

Any thoughts from the group on this subject would be welcome.



Andy Saulietis / ISS Alt-Az-Fp Drive Systems
HDPE Worm Gears, Custom designs & Machine work
29 Serenity St  Mayhill NM 88339
505-687-3067 Voice
505-687-3021   Fax
e-mail: iss@pvtnetworks.net
32 54 13 N  105 31 44 W 7300' elev

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