" ...When collecting PEC data Autoguiding needs to be turned off otherwise it corrects the imperfections and the PEC collection process is ruined, but once you have collected and applied PEC there is every reason to want to continue using Autoguiding !
PEC only attempts to correct for the irregular "bumps" in pure sidereal movement, primarily caused by the normal mechanical deviations from perfection that exist in almost all gears made by man !
eg most spur gears are cut with 3-5 straight or semicircular cuts to approximate a curve that is an involute curve.
Hence PEC tends to be almost entirely aimed at the complex combination of all the different periods of rotation for each gear in the gear train.
Guiding attempts to correct for all the other errors put together - Atmospheric refraction changes with altitude, temp and barometric pressure, Sidereal tracking rate errors, backlash and other mechanical errors that include incorrect polar alignment.
So anything that can reduce the job the autoguiding correction does is a good thing.
Hence exceptional Polar Alignment, absolute rigidity in the pier and all adapters, good quality mount, Tpoint mapping for software correction of other mount and OTA related physical errors (eg non orthogonality, flexures of all sorts, backlash . . . .) and then all sky pointing correction with software such as ProTrack.
So PEC only performs but one of the many necessary functions to try to reduce the "noise" in our image acquisition systems ... "
Thanks to the source of the above info.
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