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Last updated: 3 April 2012

Sent:	Sunday, April 1, 2012 06:58:05
From:	Mark Mittlesteadt (
After using my scope in polar alignment mode, I noticed I was getting drift
in RA. I know this is not the fault of the scope, the drive gears or
anything else, other than my own fault. The drift was getting rather
annoying at high power (as you can imagine). I realized the problem was
entirely the scope not being balanced. I would get the object in the
eyepiece and then it would drift. I discovered the drift always shifted in
the direction towards the heavy side of the mount (be it to the left or
right). I really have no way of mounting any compensating weight without
also preventing the scope from being able to clear the base near zenith.

So...I also knew that if my scope were in Alt-Az mode, the forks would
always be upright and all travel in RA would be in the horizontal plane and
the unbalanced weight of the scope would have no bearing and thus not drift.
Which of course was confirmed first night out with it in Alt-Az. It was not
the gears, not a lack of drive was simply the scope being out
of balance when in polar mode, forcing the gears to try and keep not only
the slewing/tracking intact, but also keeping the offset weight balanced
(which it simply could not do).

In Alt-Az it is perfection. Objects stay perfectly centered in the EP all
the time and remain there for as long as I want it to. With that I set out
to perfect the Alt-Az mount itself. In the two pics provided you can see
that I made a triangular mounting plate out of plywood. The bottom plate
attaches to my tripod/pier (or to any stock tripod head as well). The center
bolt (with wing nut) allows me to rotate the mounting plate to get it
pointing north (without having to move the tripod). Then the three leveling
bolts allow me to level the scope (again without having to level the
tripod). I suggest using leveling bolts no smaller than 1/2" in diameter to
ensure there is no vibration in this setup. It is rock solid. 

The top plate attaches to my ETX scope base (which still fits in my case).
The bottom plate stays mounted to my tripod/pier). I simply set up my
tripod/pier and eyeball it relatively level (no need to make it perfect) and
one leg pointing relatively north (again, no need to be exact). Then I set
my ETX105 on the mounting plate (with the bottom plate's leveling bolts
going through the top plate holes). Then I can rotate the assembled mounting
plate to precisely north and lock it down tight (with the wingnut). Then I
level the scope using the bottom nuts of the bottom plate's leveling bolts
(under the washers the scope and top plate sit on), and once level, tighten
down the top nuts to lock it down.

No fussing with the tripod in any way to achieve polar north or leveling, or
having to mess with attaching the scope to the mount. Easy and rock solid.

Thanks again for your site providing such great ideas for us ETX users. I
hope this is helpful to anyone who might like an easier solution to using
the ETX scopes in Alt-Az mode. This mounting plate will work with any pier,
stand, base, tripod or tripod head (with some slight modification perhaps).
Anyone can e-mail me for more info on it. It is VERY easy to make.

Mark Mittlesteadt
2nd Nature Creations LLC



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