Strange guiding errors with AP1200

Allen Gilchrist

Has anyone else seen anything like this before?  During an imaging session with my AP1200, while guiding with an STi on a 400 mm f.l. 80 mm refractor, I noticed an occasional really large guiding error.  It took a few cycles to bring the guidestar back to the center of the guide window, and then all was OK until it happened again.  I started an autoguider log file, and found that the process repeated every 379 sec.  This suggested some problem in the RA drive system, but there were corresponding spikes in the Dec. error log as well.  In fact these errors were larger than those in RA.  It almost looked like something was binding the RA drive every 379 seconds and then, when the drive slipped free, there was an impact on the Dec axis.  Interestingly, after recording five of these events in the autoguider log, the problem vanished.  I continued observing for about another hour and a half but the problem did not return.  I've attached a couple of plots, one showing the problem, and the second one after the problem went away.  The plot scale is in pixels, and each pixel is 3.82 arcseconds.  Any ideas?


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