Periodic Error Correction Results with the CGEM
March 24th, 2010
I thought I’d publish my results from measuring and training PEC on my CGEM, other users may find the results useful as might potential buyers. I used PEMPro after researching the subject as it is generally thought to give the best results, though I had a bunch of issues getting it to work properly with then SPC900NC webcam, see my earlier post on that subject if you are having problems.
PEMPro offers full support for Celestron mounts as well which is handy, allows you to directly upload a PEC curve to the mount. Anyway, on to the results, the first screens show the uncorrected curve written after 5 worm cycles.
Individual worm cycles :
PEC Curve :
The reported periodic error is +14.2/-13.0, certainly enough to give me problems with extended stars on the RA axis at my image scale, though guiding corrected a reasonable amount of this it was not perfect by any means.
The PEC curve created from this data was then uploaded directly to the mount and I took another set of two worm cycles with PEC running to get an idea of the improvement.
Individual corrected worm cycles :
The data shows corrected periodic error of +5.5/-5.1, a great improvement and a 5 minute guided exposure afterwards showed much better stars, and also showed up how badly out of collimation the scope had become during the recent pier installation. There are probably better results to be had with more worm cycles of data, and I’ve not looked into smoothing the curve or adjusting the time shift, but I’ll report back when I do.
Thanks for publishing this. I’m considering upgrading to a CGEM and this was just the info I was looking for.
No problem Keith, I think there are better results to be had from the mount with more cycles, but finding the time to do the work with the current weather conditions is always a challenge.