I'm using EQMod driver to drive a Skywatcher AZ-GTi directly, without any other interposed software. It works pretty fine, but I've seen that the errors are not uniformly distributed. They cluster around clumps separated by 4" or so. I've attached a screen shot showing the drift plot.
My question is, anybody has detected a similar pattern? Could it be related with the mount? Can I do anything to have a better behaved system
What I think is very suspicious is that the distance between clusters, about arcsec, is just the resolution of my guidescope/CCD combo: each pixel on the CCD is just 4 arcsec of sky. If you look in detail at the drift plot, you can see that the guide frames are clustered on a regular square grid of 4" of side... just the pixel pattern on my CCD.