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Adjusting the Index Mark Locations on the AS-GT Mount
(AS-GT Misses First Two Alignment Stars by a Wide Margin)

When using the Auto and Auto Three-star Alignment routines on the AS-GT, the mount assumes the following:

  • The RA axis is roughly polar aligned - many sight through the RA axis' tube (this tube is for installing an optional polar finder scope) to center on Polaris
  • The tripod is level - this is required to insure the RA index point is correctly oriented with the sky
  • The location, date, time, daylight savings time and time zone settings are all accurate
  • The index marks are correctly aligned

This last item turns out to be a bit of a problem with many AS-GT scopes.  Many scopes seem to have come from the factory with the index marks in arbitrary locations.  Inaccuracies in any of these three items will result in the scope missing the first two alignment stars significantly.  It should always be very close to the third star since the first two stars build the model of the sky and the third star is simply used to calculate cone error (see the manual for an explanation).

The marks should line up when the optical tube is parallel to (in line with) the RA axis (this is done by moving the scope in declination) and sitting directly on top of the mount (this is done by moving the scope in right ascension).  The figure to the right shows the basic orientation of the scope at this location, although the optical tube is pointed a little off from parallel with the RA axis.  Note that one way to insure the scope is sitting directly on top of the mount is to use a small "torpedo" level placed vertically against the flat side of the
declination axis housing - the location pointed to by the arrow in the figure on the right.  Then use the 90 bubble (see the figure to the left) to properly align the RA axis.

You can check this indoors and then either move the index marks or apply tape along each side of the split and draw a line across to indicate the correct location.

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Michael Swanson
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