Saturday, April 17, 2021

Joy and Frustration

Everytime I roll out the 8" f/7 reflector my father and I made, I marvel at the precision of the mirror.  Even at 354x, the Moon is spectacularly sharp. Generally a reflector should only give a good sharp image to about 50x/inch and even then you usually need very good seeing (low turbulence and limited moisture).  I have used this telescope to 700x under very exceptional conditions.   Partly this is because Coulter was in the high precision mirror business back then, advertising +-1/25th wave mirrors. (That is a measure of how close to a perfect paraboloid the mirror in wavelengths of light.)

While more precise than Big Bertha it lacks the light gathering power.  Big Bertha gathers 4.8x the light.   The Orion Nebula is clearly green through it.  The Ring Nebula is a green ring instead of monochromatic. The one time I hit the Whirlpool Galaxy the detail in the arms was worth there unreasonable amount of time and money that I have put into it. 

I believe I mentioned trying to rebalance the 8" tube on the mount a couple days ago.   It is perfectly balanced but needs rotation in the rings to get the focuser and finderscope a bit more usefully located.

The frustration is that the CI-700 mount on which it sits seems to be having a problem with the hand controller. This is a four button box that plugs into the mount electronics to let you make very fine adjustments in position.   

Right now, one button works.  As you might expect, replacements for this mount are scarce if available at all.  The hand controller for my Losmandy GM8 looks identical and may in fact be the same.  I will try it.  If it works finding a replacement GM8 controller should be easier.  Otherwise I will open the box and looks for dead bugs.  Without a schematic I doubt that I could identify much less repair it.

The RA motor turns but the polar axis sits there placidly.   I think I will buy a new mount (Losmandy, American made) and let someone else debug this Chinese orphan.  Celestron is of no use with a 20 year old product. 


  1. IF it is just buttons (switches) then it should be easy to trace....and repair, either by find ing a new switch or replacing the switches and making a new enclosure for them.
    Or it could be a bad connection in the cable or the connector.

    You should be able to find out (if it is just switches) what it is with an ohmmmeter.

  2. The hand controller is working. At 16x speed I can hear the motors on each axis whirring. There is some subtlety with the clutches I fear.

  3. You may need to expose the gear train of the motors to trobleshoot. They tend to be brass for small motors, and with enough stress they strip teeth. Sometimes this results from the mating gears not being positioned to get full width engagement. Other times it is from being loaded too close to the limits of the gear train, and then having to deal with the added stresses of poor assembly and maintenance with aging mounting components.