Jump to content


Photo

Need advice from mount gurus on an RA issue (?)

  • Please log in to reply
2 replies to this topic

#1 astrovienna

astrovienna

    Surveyor 1

  • -----
  • Posts: 1770
  • Joined: 04 Dec 2006
  • Loc: The NoVa White Zone

Posted 05 May 2011 - 12:23 PM

Last night I collected data on the unguided behavior of my CPC1100. With PEC on, the mount shows a 10-12 arcsec cyclic drift roughly in sync with the 480 second worm period. You can see a graph here:

http://www.pbase.com...image/134462963

Because it's in sync with the worm cycle, I'm guessing it's residual PE not fixed by PEC. Any suggestions on reducing this further? Do I just need to redo my PEC? It's about a year old (and I did the CPC bearing replacement last fall). When I last did my PEC, PemPro reported residual error of only 5.3 arcsecs, not 10-12.

I'm actually pretty satisfied with my typical guiding results:

http://www.pbase.com...image/134462962

but near the equator I do sometimes get RA elongation. I suspect reducing this residual drift would help.

As for the apparent cycle in dec, I suspect that's an illusion created by less than perfect calibration in PHD. For example, if the real angle for dec is, say, 84 degrees, but because of miscalibration PHD concludes it's 76 degrees, PHD is going to attribute some of the RA drift to dec, and graph it that way. I guess this shows the importance of good calibration.

Man, I need a Mount Whisperer!

Kevin

#2 rmollise

rmollise

    Hubble

  • *****
  • Posts: 15778
  • Joined: 06 Jul 2007

Posted 05 May 2011 - 04:33 PM

Last night I collected data on the unguided behavior of my CPC1100. With PEC on, the mount shows a 10-12 arcsec cyclic drift roughly in sync with the 480 second worm period. You can see a graph here:

http://www.pbase.com...image/134462963

Because it's in sync with the worm cycle, I'm guessing it's residual PE not fixed by PEC. Any suggestions on reducing this further? Do I just need to redo my PEC? It's about a year old (and I did the CPC bearing replacement last fall). When I last did my PEC, PemPro reported residual error of only 5.3 arcsecs, not 10-12.

I'm actually pretty satisfied with my typical guiding results:

http://www.pbase.com...image/134462962

but near the equator I do sometimes get RA elongation. I suspect reducing this residual drift would help.

As for the apparent cycle in dec, I suspect that's an illusion created by less than perfect calibration in PHD. For example, if the real angle for dec is, say, 84 degrees, but because of miscalibration PHD concludes it's 76 degrees, PHD is going to attribute some of the RA drift to dec, and graph it that way. I guess this shows the importance of good calibration.

Man, I need a Mount Whisperer!

Kevin


How are you recording and applying PEC? If you are not using Pempro, do so.

#3 astrovienna

astrovienna

    Surveyor 1

  • -----
  • Posts: 1770
  • Joined: 04 Dec 2006
  • Loc: The NoVa White Zone

Posted 05 May 2011 - 08:28 PM

Hi Rod! Yeah, it was PemPro. (I should have mentioned that the details were under the graphs.)

Kevin






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics