Monday, December 28, 2015

Fixed: Meade ETX-70 Slop and Fat Finger Focus problems

A few months back I got a Meade ETX-70 Computer Controlled Telescope.  It's a fun toy, and for $30, I couldn't beat the price.

When I tried it, I found a couple of problems.: one with aiming, and two with focusing.

First up is an aiming problem, and it's not the telescope's fault.  The computer control discovers its elevation and azimuth by asking you to focus on well-known stars.  Unfortunately I'm star defective, and can't tell Cygnus from an antenna tower.  This is an ongoing problem, but I'm learning slowly with help from http://www.skymaps.com/ and "Collins Wild Guide to the Night Sky" from McKays.

The focusing problems are more involved.

To focus this telescope, there is a small (less than the diameter of a dime/1.5 cm and ~2 cm long) focusing knob near the eyepiece.  There are two problems with this.

First, when the telescope is vertical there is no way to reach the focus knob with my giant ogre hands.

I fixed it.  With the disassembly instructions from http://www.weasner.com/etx/, I manufactured a flexible replacement for the focus knob.






The replacement is made from a flexible piece of plastic jacketed steel cable, a turned steel coupler, and the original focus knob.  It lets me focus even at the extreme of the vertical travel.

Second, on my telescope, was the obscene amount of backlash in the focus adjustment.  If I was turning left and overshot, I'd have to turn back right 8 turns before the lens would respond.  That sucked.  Disassembly and reassembly helped with this, but I wanted a more permanent fix.  Here it is.


I shortened the adapter enough to fit in a thin brass washer.  This washer is bent, to provide some springiness that takes up the backlash in the focuser.

I just finished it and am really excited to test it.   Sadly, Murphy's law says...
... it will be a while.

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