Last updated: 17 December 2005
Subject:	Improving DSX goto accuracy
Sent:	Thursday, December 15, 2005 20:14:07
From:	Bill Swartout (
I found a little trick that seems to have improved the pointing accuracy
of my DSX-90 scope and I thought I'd pass it along. In the book "How to
Use a Computerized Telescope" the author, Michael Covington points out
that one of the factors that can adversely affect pointing accuracy is
nonperpendicularity. That is, the alignment software assumes that the
azimuth and altitude axes are perpendicular to each other and that the
OTA is perpendicular to the altitude axis. If that's off, pointing will
be less accurate. On the DSX scopes there's no easy way to adjust the
azimuth and altitude axes with respect to each other, however, because
the telescope is attached to the mount with two thumbscrews and the slot
the screws run in has some play in it, you can adjust the OTA to get it
perpendicular to the altitude axis.

Here's how I adjusted mine:
1) put a bubble level on the flat part of the telescope base (just in
front of the battery cover).

2) Level the tripod until the base is perfectly level.

3) Release the altitude clutch and rotate the OTA until it is pointing
straight up.

4) With the metal lens cover in place on the OTA, put the bubble level
on the lens cover.

5) Loosen the thumbscrews attaching the OTA to the mount slightly so
that it can be wiggled a bit back and forth.

6) wiggle the OTA back and forth until the bubble level shows that the
lens cover is perfectly level.

7) Tighten the thumbscrews

Following the procedure I found (in admittedly limited testing) that
objects were consistently in the 26mm FOV. Before this adjustment, I was
only getting object in the 26mm FOV about 50% of the time.

I'd be interested to hear if others have luck with this.


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