Mount Periodic Error

I finally learned how to correctly measure periodic error of German Equatorial Mounts.

Some of the things I've learned: you need to turn off guiding output in PHD, otherwise what you are measuring is the error with auto-guiding turned on. And, you need to correct for the declination of the star you are guiding on (stars closer to the poles would show less periodic error as they move through shorter "arcs").

I've also learned how to use WebCamScheinern for somewhat automated drift polar alignment, and managed to get good alignments these past two weeks. And, I've also learned to use PEMPro (albeit a trial version for now) to measure periodic error and generate the curves.

With that said, here are the periodic errors of the three mounts I currently own. The Vixen Polaris is gone, sold to a guy in Manila, and I wouldn't bother measuring the periodic error of the Orion EQ-1 that's rusting under the sink.

Vixen Great Polaris with DD-1 stepper motor controller and two MT-1 steppers:



That's a whopping 85 arc-seconds peak-to-peak! a far cry from the 20 arc-seconds I wishfully "measured" some months ago..

Celestron CGEM:



29 arc-seconds peak-to-peak. Not too shabby, and smooth enough.

Astro-Physics 600E QMD, probably manufactured when I was still at university:



7.84 arc-seconds peak-to-peak. A pretty good figure, although I believe the G11 can match or exceed this performance (a used G11 would also cost a bit less, and crucially, carry much more payload). I'm trying to upload the PEM curve to this mount and see how low that figure can go..