Wednesday, July 11, 2018

Glad I Fixed This Monday

I was struggling with the finder crosshairs adjustment Sunday night with the new finder on Big Bertha 3.0.  I wasn't sure if it was tiredness or that the mechanism for adjusting point of aim is a new one that seems impossible.  Traditional telescope finders had two rings holding the tube with three thumb screws in each ring.  Of late, Celestron has switched to a scheme with one ring, two thumb screws and a third spring loaded screw that you cannot adjust.  There is a front ring with a big piece of soft rubber between tube and ring.

Complicating this, the finder assembly slides into a metal base that is held to an adapter to the telescope.  Traditionally, finderscope rings attach directly o the telescope tube.  With a semi-serrurier tube, there is nothing solid to which to attach the rings.  Dobstuff.com, who rebuilt my sorry experiment with Big Bertha 2.0 into the current telescope, attaches the rings to a wooden base which clamps onto a 1" aluminum tube at the front of the upper cage.  I had to replace the wooden base with a new one because the old finderscope tube was much longer than the new one; and because I decided the black acetal would be tougher and better tapped.  It was also nice to be able to make this part with a "just barely fits" slot using the mill.

So I started trying to adjust it, using a radio station tower on top of Bogus Basin as my target.  First, I noticed the front rubber ring was not seated between metal ring and tube.  Then I noticed the finderscope's base was loose on the acetal adapter.  After removing everything, I stuffed the rubber between the tube and the front ring, and tightened down the nut and screw that holds the scope base to the acetal plate.  (In computer science terminology: interface to the interface to the interface.)  Now, those two adjustment screws are easy to exactly center the target into the dual illuminated crosshairs. 

No, three are no mildots; is it really a "windage" adjustment when there is no wind out there?  When I first built a 3" f/4.5 reflector some years ago, the people I worked with assumed that it was a weapons scope.  And why would you need that much power for something that you can pick up and carry?  Of course this was the S.F. Bay Area, where many otherwise educated people might have difficulty identifying from which end the bullets come.

1 comment:

Stephen said...

Start a rumor that the 3" reflector is a copy of the optics on Isaac Newton's home defense gun, then change the subject. Quickly.