Quote:
Originally Posted by Ryderscope
Lee, there is a discussion ( link here) on the EQ8 Yahoo users group on Periodic Error. The post shows that they were seeing about 8" periodic error as measured using PECPrep which is consistent with your results. I haven't read further yet to see what improvements might be gained by implementing PEC.
I am interested in following this discussion as I am about to start tweaking the polar alignment of my EQ8 and have been contemplating the implementation of PEC as well. I have just moved from a 900mm refractor to an RC10 with a 2 metre focal length and I can see now that the tracking is not quite as good as I would like it to be. |
Thanks Rodney :-) Having acquired an old RC8 with a 1.8m focal length somewhat recently myself I know the feeling. It's not an easy task, but I think with the EQ8 we'll get there :-)
Quote:
Originally Posted by Shiraz
mine measured at 7 arcsec p-p in PECprep as well, with two regions of fairly rapid change. These guide out OK at my typical seeing and at 0.91 arc sec sampling.
attempted PEC as follows:
1. autoPEC - why not give it a go I thought... It generated a reasonable curve, but assumed an EQ6 worm period. I redefined for an EQ8, but the new auto curve had a phase error????.
2. then tried using PECprep with data out of phd (not phd2) - it has to be done exactly by the book. I got a good curve that was very consistent across 5 worm periods and almost removed PE entirely in the simulator, but it had a phase shift as well and I could not get it synchronised, even though I had done time stamping and parking. The phase shift slider did not allow shifting across the whole of the worm cycle, so something? was clearly not quite right.
3. Then both phd and phd2 stopped guiding properly - presumably because EQMOD was applying crap PEC as a carryover from an earlier attempt. disabling PEC did not help and I could only get it all back working by reloading everything.
when I get another marginal night and bit more courage, will try again with PECprep, but not with autoPEC. I don't think it is actually too difficult, but everything has to be done exactly by the book. Rate based PEC is in principle a great idea and should clean up the PE very effectively. In the meantime, I get about 0.6 arcsec RMS guide error at 1 sec update on a good night, which is fairly good anyway.
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Thanks Ray! Sounds like a pain in the nether region, really, but maybe worth it in the end.
I read on another forum of a woman who was using her EQ8 to get very long unguided subs (30mins before trailing started to show if I recall correctly, and I think at a long FL as well). I made the (fairly reasonable, I think) assumption that she was achieving this by applying PEC, thus my sudden interest.
Given that, I thought I'd try PEC myself, as if I can get away without guiding, I'd rather do that. For broadband imaging I think I can get away with 220 second subs, which I'm hoping might be achievable at 1.8m FL with PEC. I guess we'll see!