ETX TECHNICAL TIPS
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 ¼ /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
Return to the top of this page.
Go back to the Tech Tips page.
Go back to the ETX Home Page.