Kevin_A I often wonder how well zwo is with centroid accuracy… it has always been my feeling that the asiair is not that accurate.
I should have more data coming soon.
While trying to gather RA guding data (only the RA axis of the RST-135E has the Renishaw encoder), I also re-polar aligned (after almost a year :-).
As a result, my guide graphs show pretty flat declination slope with the declination guiding completely turned off. Except for the noise riding on that flat-line. Since no one is moving the declination axis (and I have the camera angle aligned with the equatorial coordinates), the noise must come from centroid estimates.
I am concurrectly writing a program to measure what I get from the PHD2 logs. But at some point, I am hoping to also see what the centroid noise from ASIAIR is.
BTW, tonight's experiment uses the FRA300 as the "guide scope" to get PHD2 logs :-).
The problem is that the period of the error is so long (430.82 sec) compared to the sampling rate (2 FPS), an FIR filter has to be really long to be able to filter out the RA drift component from the 430.82 cycle). And that means taking a couple of hours worth of data just to get perhaps 8 periods worth of filtered data from the PHD2 log. So,, long nights of data collection, and can't have a meridian flip in between :-).
I am also measuring right at the equator (well, within 1 of the equator) to get the actual RA error instead of the cosine of the RA error (notice that RA guiding error improves as you get near the pole -- when the declination is +90º, the RA error should be 0 (except for the centroid noise). So, in total, there is only a small part of the sky that is useful for mesuring :-).
By the way, if there is any anomaly in RA (gear tooth missing or deformed, etc), it should always happen at the same hour angle of the mount (i.e., angle of the RA axis relative to Meridian) and independent of the declination angle.
Anyway, the YouTube shills can apparently make all these measurements in one night! What people will do for money! Some people have no shame (at least that OPTcorp shill is out of one of his sources of income now :-).
Chen
