Last updated: 4 February 2002
Sent: Monday, February 4, 2002 16:21:39 From: firstname.lastname@example.org (Thomas Henry) While observing and star-testing last night, something surprising happened. At the start of the night the star tests were quite good (circular images when defocused). Several hours later I saw the typical tri-form image caused by pinched optics. Why the change? Well, I'm in Minnesota and last night was quite cold (around 5 degrees or so). You southerners will never know the joy of touching metal parts that literally sting like electrical shocks! Anyway, it's pretty clear the optics were not pinched when warmer, but the cold air compressed something or other. I built a spanner in a matter of minutes which lets me loosen up the retaining ring. When I used it, I found that the ring was indeed really cranked down. So much for Meade's constant reference to "to a firm feel only"! Backing it off a bit eliminated the tri-form pattern. To make the tool, I used 1/2" by 3/4" pine parting strips, and 1/4" dowels. I clipped the heads off some brads to use as metal pegs. After clipping these, I filed them down to remove any burrs and to smooth them off completely. Pilot holes in the end of the dowels permit you to tap them in. See the attached photo. To use it, the metal pegs slip into the two index holes on the retaining ring; just revolve the spanner as desired. By the way, the spread is exactly 3" between the centers of the metal pegs, for the ETX-70AT. Here is a good reference to pinched optics and how to deal with them:
Best wishes, Thomas Henry
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