denababy I polar align, getting it as close as possible, but when I slew to a target it’s in the vicinity but not on target
Polar alignment is the process of getting the polar axis adjusted so that the polar axis of the mount is parallel to the earth's axis. It allows the mount to track stars as the Earth rotates around its own axis.
Polar Alignment is necessary, but insufficient to achieve GOTO precision of your mount.
For GOTO, you need to also make sure that when the OTA (not the RA axis) is asked to point to the Zenith, the mount's motors will direct the OTA there.
To do this, your mount needs the be perfectly level, and if your mount does not have either (1) absolute encoders on both RA and declination axes, or (2) relative encoders with index marks which are perfectly calibrated, and perfect sidereal time (or UTC + perfect Longitude), then you would need to use stars to calibrate the mount's motors (so called Star Alignment). Star Alignment is the poor man's substitute for an absolute encoder -- i.e., it uses stars instead of index marks on a glass plate to supply the position of the motors.
However, that is what Plate Solves are for. After a GOTO, do a Plate Solve (which identifies the center of the OTA camera, computed from star asterisms), and with the ASIAIR, tap on the "Sync And Goto" button. The Sync will tell the mount that the OTA is not really pointed to where you want it to move to, and the GOTO will command the mount to move relative to that Sync position. If you are off by a lot, then you have to do multiple consecutive plate solves, each followed by a "Sync and GoTo," to get within what you consider usable tolerances. How close you can get will also depend on backlash in your gears and the precision of their teeth.
Chen
