Using a secondary scope to track

[john.clark]

I'm a bit of a novice at tracking.  At low magnifications with my DSLR piggybacked I get along just fine.  At higher magnifications with my 8" Newtonian and a secondary scope attached to it, the image jumps a lot every time the tracking corrects.  I need to fine tune this somehow, but I don't really know how.  My mount is a HEQ5 with the "Rajiva Update" electronics.

I'm using Guidemaster software.  I can play with the aggressiveness of the tracking, which helps a bit, but not enough.

Any suggestions? 

Thanks,

John.

[RobertM]

Hi John,

I'm not familiar with either the HEQ5 or Guidemaster but I suspect the main causes are because there's backlash in either or both axis.  Other than adjusting so that the worm meshes more snugly with the wheel you should try to set the balance so that the drive is always pushing i.e. heavy on the east side by about 1lb, this might eliminate some of if it.  A similar weighting should also be applied to the Dec axis but that's more difficult to determine.  If your scope is perfectly polar aligned then turn Dec corrections off, if otherwise then drift will be north or south so turn off one or other of the corrections.  Another possible cause is stiction because the axis aren't able to move freely; a strip down and relube might be the only answer in that case.

Nearly forgot - make sure there is absolutely zero flex or movement of one scope relative to the other.

Maybe someone with one of those mounts could share their guiding experiences.

Hope that helps
Robert

[john.clark]

Hi Robert:

You've got me thinking.  I never really thought about separating the RA & Dec issues.  They are both there, and I think the Dec may be worse.  Perhaps the 'always pushing' principle may apply to Dec as well: I could try deliberately misaligning it with the pole slightly, so that it drifts and let the guiding correct the drift.

Thank you for your thoughts.

Regards,

John.

[MarkS]

John,

I used to have this problem.  You need to set the change the amount of backlash compensation in the handset options.  I'm not familiar with Guidemaster but for PhDGuiding you must set it to zero (in both axes) because PhD calculates its own backlash compensation to apply.

Mark