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ES G11 / ExploreStars issues Summary


Jeremy Parker
 

Hi Chris,

This is my original post, and I'll be eventually writing a report to summarize it, but here's the short version:

During my first time out with the mount, not yet auto-guiding, I saw star trails in even 2 minute exposures. I was using the PoleMaster for the first time as well, and was trying to seperate any potential polar alignment problems. I was also having intermittent issues getting star-aligned with ExploreStars.

I set my camera up so that RA movement would be in the left-right direction on the frame, and DEC would be up-down. Then I took a series of exposures at different lengths to see how the star trails might change over time. It turned out that I had a good polar alignment, but both high periodic error and RA drift. The incorrect 'RA Rate' setting in ExploreStars was to blame for the RA drift problem. I still don't know how it happened, but once I put the correct value in, the RA drift was fixed.

Then the remaining issues were due to higher-than-expected periodic error, which Jerry and myself attempted to measure by counting pixels and analyzing my images. Then eventually when I got my guiding scope/camera, I was able to measure it with PHD2. It was around 36" peak-to-peak, at it was causing my stars to appear oblong. 

I was also having issues with balancing my mount in RA, due to the friction present by the weight of the setup pushing down on the RA clutch. The solution there was to get a RA wavy washer from Losmandy, which 'unwieghts' the RA enough to let it rotate smoothly, until the clutch is tightened. It was then easier to determine the east-bias for the setup.

The root cause of the high PE was some misalignment of the RA worm bearing blocks but mostly due to a bent helical coupler. I've replaced both DEC and RA couplers with high-end Ruland equivalent couplers, and I believe I've minimized the problem and have the mount performing in-line with Jerry's expectations: around 16" peak-to-peak.

Hopefully this makes it a little clearer to follow...
Jeremy