Last updated: 10 May 2001

Subject:	Balancing Your Fork-mounted ETX or LX 90 is Crucial
Sent:	Thursday, May 10, 2001 01:29:37
From:	sherrodc@ipa.net (Clay Sherrod)

Lately, with more and more accessories for the ETX and LX 90 telescopes
being offered in the marketplace, I am getting inquiries regarding the
importance of BALANCE of the telescope and its mounting for proper use
and continued good service of the telescope system over time.

Also, I am beginning to see coming in for my Supercharge tune ups MANY
telescopes whose mountings are suffering badly from excessive wear and
slop due to use in severely imbalanced conditions over time.

Indeed, improper balance of the fork-mounted ETX or LX 90 telescope is
crucial and definitely WILL adversely affect accuracy, GO TO's tracking
and random slewing conditions if balance is not maintained in BOTH axes.
In addition, it will greatly shorten the precision and life-expectancy
of your tracking system as well.  This is particularly true, more
difficult difficult to achieve,  and perhaps more crucial  when your
telescope is mounted in POLAR mode.

In Alt-Azimuth, care must be taken for good balance (you want a little
"load" on the front of the optical tube assembly to assist in
maintaining minimum backlash of the mechanical aspects of the
drive/slewing motors), but primarily in the ALTITUDE axis.  In Polar,
balance should be achieved in both Declination (altitude) and Right
Ascension (azimuth) axes and is not easily done, as the center of
gravity will shift on you in different parts of the sky.

This is particularly true when heavy accessories are added to the front
or back of the telescope optical tube assembly, such as the electric
focuser, a piggybacked camera or guide telescope, a heavy eyepiece (such
as Meade's heavy 14mm UWA) or a camera body mounted at the prime focus
of the telescope.  It does not matter whether you are using the ETX 90
or the LX 90.....balance is important and crucial to the life of the
mechanical parts of your telescope!

In Alt-azimuth mode, you must simply unclamp the altitude ("up-down")
axis prior to observing and check to see if the telescope tube unduely
wants to swing one way or another too freely;  merely add an appropriate
amount of weight to the opposite end (usually the front end if a camera
or other heavy accessory is added) until the excessive weight seems to
be compensated for.

The fork mount balance point will CHANGE as your direction pointing
changes in the sky in Polar mode and hence the sliding counterbalance
systems are necessary in the LX 90  to compensate for this shifting
center of gravity.  On my LX 90 I have an 80mm ST refractor piggyback,
the #1206 heavy focuser, the 2" diagonal and the heavy aluminum Meade
dew shield (plus a few tin cans hanging on it from time to time) and
balance is always a problem and will most definitely cause poor tracking
as well.

If using Polar  - and more and more ETX and LX users are doing just that
- adjust your balance according to which position of the sky you are in;
since you cannot unclamp your LX 90 once you have gone to a position
(you will lose your alignment) you must do this through trial-and-error;
I do this in the daytime and make notes of what is required in
"southeast", "near-meridian", "northwest" and so on, sketching little
diagrams of what weight is necessary where after a GOTO....then I merely
add on the weight while the drive is running after each GO TO and the
scope does fine.

You will notice from some trial-and-error balance testing that many
times you may be well balanced in declination, yet your right ascension
(your main driving axis) is severely out of balance....this can be
particularly true when pointing the telescope far southeast or southwest
with heavy accessories on the eyepiece end.

If you do not balance properly not only is your accuracy and tracking
affected, you will slowly wear out the small motors, add looseness to
your gear trains and cause excessive slow in your clutches.  Take care
of your ETX or LX 90 telescope by assuring proper balance at all times
and in all positions!

P. Clay Sherrod
Arkansas Sky Observatory

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