LX200 Frustration

  2004.12.02

Today the STI Stiletto Focuser showed up at my place and Bob received the STV CCD autoguider system. Two very cool toys. We were both really excited to play around with them so as soon as Bob got out of his lab at about 8:00 we got together and set up his telescope in his back yard.

Because we were at his house it was pretty much impossible to forget anything, so unlike last time we had a printout of the polar alignment procedure. Unfortunately, we ran into a snag before we ever got to the drift alignment portion of the procedure. We got the tripod roughly aligned and leveled, then got the wedge centered and the LX200 placed on it. As indicated, we turned the scope on and trained it on a southern star near the meridian and about 30 degrees up on the horizon (Menkar aka Alpha Cetus, in this case). After synching the scope on Menkar, we were instructed to have the scope GOTO Polaris and then refine the alignment using the wedge knobs.

When we hit the GOTO button, the scope would get a GPS fix, then slew into some random and very wrong position, often hitting the DEC stops or pointing straight into the ground. We could not figure out what was wrong. We tried for three hours to modify the routine slightly so that the LX200 could figure out where it was but it was no use. All of our GOTO attempts were always disasters. In the end, we had to shut down at 11:30pm because both of us had to get up early in the morning.

  2004.12.03

After researching the problem we have discovered the missing step. When you turn the LX200 on, it assumes that the DEC axis is at 0 degrees (perpendicular to the forks with spotting scope on the side away from the base) and that the RA axis is set to the current time. The expanded version of the instruction sheet we had mentions this, but the field document we were using does not.

We're going to print out a revised edition of the accurate polar alignment procedure specifically for the LX200GPS (the version we have doesn't deal with the GPS acquisition). We'll have to test it to make sure it is correct, but right now it looks something like this: [updated again on 2004.12.05 to totally separate the computer alignment from the mechanical alignment]

  1. Orient the tripod roughly N/S.
  2. Level the tripod.
  3. Mount wedge and center the azimuth adjustment.
  4. Make sure the wedge elevation adjustment is set for roughly the correct latitude.
  5. Insert the three Tripod/Wedge support bolts but do not tighten.
  6. Mount LX200GPS on the wedge.
  7. Insert and tighten two additional LX200/Wedge support bolts.
  8. Set the RA axis to South (forks pointing North), tighten axis lock.
  9. Set the DEC axis to 0 degrees (perpendicular to the fork), tighten axis lock.
  10. Turn on the LX200GPS.
  11. Center the microfocuser.
  12. Check that the LX200GPS is set to POLAR mount.
  13. Go through the 2-star alignment procedure.
  14. Save current location in memory if not already there.
  15. GOTO Polaris.
  16. Use wedge knobs to get Polaris roughly centered in eyepiece.
  17. Ensure that a diagonal and illuminated reticle are being used.
  18. Use hand controller to point to a star on meridian about +20 degrees DEC.
  19. Rotate the eyepiece until the linear scale runs E-W (using HBX to pan in RA).
  20. Let the telescope track and watch for drift in DEC.
    • If the star drifts up, turn the wedge AZ knob that makes the star move right.
    • If the star drifts down, turn the wedge AZ knob that makes the star move left.
    • Recenter the star using the hand controller.
  21. Repeat previous step until there is no DEC drift after 5 minutes.
  22. Use hand controller to point to a star on equator within 15 degrees of horizon.
  23. Rotate the eyepiece until the linear scale runs E-W.
  24. Let the telescope track and watch for drift in DEC.
  25. If looking at the Eastern horizon:
    • If the star drifts up, adjust the elevation to move the star down.
    • If the star drifts down, adjust the elevation to move the star up.
    If looking at the Western horizon:
    • If the star drifts up, adjust the elevation to move the star up.
    • If the star drifts down, adjust the elevation to move the star down.
  26. Repeat previous step until there is no DEC drift after 5 minutes.
  27. If the overall correction to elevation was several degrees or more, recheck azimuth.
  28. Tighten the three Tripod/Wedge support bolts.
  29. Turn off the LX200GPS (the wedge is now correctly polar-aligned).
  30. Set the RA axis to South (forks pointing North), tighten axis lock.
  31. Set the DEC axis to 0 degrees (perpendicular to the fork), tighten axis lock.
  32. Turn on the LX200GPS.
  33. Go through the 2-star alignment procedure again.
  34. The computer is now aware of its position. Scope is ready to go.