Hello folks,
I have the latest GM811.? A few weeks back, I posted about adjusting the screw to get the backlash as low as possible, mechanically.? When using the mount for long-exposure imaging, there are still some DEC issues that ruin a frame here and there.? I have the clutch pressure set very low.
0) First, I should mention that sometimes when the seeing is good, the guiding is good too at < 0.6 rms and the DEC axis just gives gentle nudges back and forth to the axis and everything is fine.
1) Sometimes a large DEC pulse (when changing direction) will cause a corresponding spike in RA also.? See attached picture.? Here only the northward pulses (approx 1 second worth, if I remember + TVC 10) cause a spike in RA.? (BTW, I also had these spikes with TVC 0) I noticed when running the backlash test in Guiding assistant that the guide star also moves a little in RA when changing DEC direction from N to S.
2) a dither move in DEC seems to "unsettle" the axis, and it seems to misbehave for maybe the next 30 seconds or more.? It's like the axis builds up "sticktion" and then releases it at some random time later.? In the picture, the sticktion amount is about 3 arc-sec.? After several minutes, this sticktion drops down to about 2 arc-s, and maybe if the seeing is good for a long time and I don't do any dithers in DEC, it gets even lower.? It's like the worm needs to move back and forth a few times before settling down for best performance.
So at this moment dither in DEC is unreliable because the later movement will mess up a frame.? I've resorted to dither RA only and then "manual DEC dither" after a sequence of images.
