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Does anybody experience the same? When guiding RA with PHD2 (DEC has no motor), I am experiencing periodic oscillation showing in DEC (I am not talking about RA) with p-v over 12 arcsec, sometimes even more (see the first picture, DEC curve is yellow). Polar alignment is close to perfect as shown in second picture when the RA guiding is turned off and guiding advisor is running. Is such large Declination oscillation normal or is my Sky Guider faulty? I am talking about declination only. I appreciate your insight!   |
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Hi Tomas: I've not used the guiding advisor, so I'm not sure I follow what's happening in the second image, but your first image looks VERY similar to how my Skyguider guiding graph normally looked, with the long wandering DEC patterns. Sometimes mine would wander right off the graph and I would check my guiding and see RA only for most of the evening. Sometimes the DEC would hold still for several 6-minute subs only to slowly wander away again. My PAs were pretty tight. In the end, my stars were still mostly round when reviewing the subs - I was able to keep about 80% of my 6-minute subs. I upgraded to the William Optics base (best upgrade I ever bought) and I was sometimes able to keep 100% of my 6 minute subs, and I even stretched that to 10 minutes. If I'm being honest, I can't remember if the WO base improved the DEC oscillation, but it did happen nearly every night, to some degree. The most important question is: how do your stars look? If your RA and DEC error balance each other during your typical exposure length (other factors like sample rate can come into play too) then this might be tolerable, or even unnoticeable. I'm really curious to see if anyone else can chime in with the reason this is happening. Is the rig sinking into the ground slightly? Is the latitude slipping? Would really love to know. CS, Mark |
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Hi Mark, thanks for your reply and confirming that you are experiencing the same. Yes, the stars are reasonably round but I have not used focal length over 200mm or exposures longer than 2 minutes. What is puzzling and I cannot explain is that without guiding commands (second picture) the DEC is perfect, but once I turn the guiding on (first picture), DEC starts wandering. If it was a simple cross-talk between RA and DEC mechanical axes, you would see it in both cases. Tomas |
