Last updated: 31 August 2001

Sun Aid for ETX

Sent:	Wednesday, August 15, 2001 19:49:24
From:	Hunterherb@aol.com
About two years ago I bought a Solar Filter for my ETX 90 from Orion
Telescope.  After using the filter a few times it was evident that a
pointing aid was required.  Looking the situation over I decided that I
could mount an indicator on the mounting block under the telescope tube
and insert a screw in the filter to cast a shadow.

I used a # 4 screw (about 0.1 inch diameter). I drilled a hole to clear
the screw taking some care (not too much) to drill into the filter rim
normal to the surface of the rim. The filter diameter itself is
oversized so there was plenty of clearance for the screw head. The
distance to the indicator is about 7.75 inches so splitting the shadow
at the indicator points you to within a few tenths of a degree. I placed
the indicator grid on the tube mounting block and when everything was
lined up I took two pieces of masking tape and ran them (one at about 10
o'clock one at about 2 o"clock) from the filter rim onto the telescope
tube taking care to follow the step at the junction of the rim and the
tube to aviod parallax when placing the filter back on the tube. I cut
the tape at the bottom of the step so alignment is quite easy. The
indicator is ruled (Using Corel Draw) with a 0.1 inch grid with an
accented central line as the reference line.

I've attached a *.jpg file that shows some of the detail. The picture
shows the setup in action, so to speak. The inset at the lower right is
a Sun's Eye view of the screw and the indicator chart.  The  /20 screw
that holds on a piggyback camera mount does not interfere with the set
up. Too bad the filter makers don't  drill an extra hole that can be
used if one cares to on an ETX 90 dedicated filter.

   Herb Schmidt
   hunterherb @ aol.com 
Sun Aid

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