AsToRm Even if PA was ok, the ASIAIR was not able to slew the mount to the target...
Polar Alignment only ensures that the RA axis of your mount is perfectly parallel to the earth's axis. You do this by changing the altitude and azimuth of the mount's base.
There is a third parameter involved, however (in a 3D world) -- it is where the Polar Axis motor thinks the Meridian is relative to the polar axis motor angle. The RA axis can be pointed at the pole, but if this angle is not calibrated correctly, a GOTO command will move the mount to the wrong RA angle.
Many mounts have an internal optical encoder or optical index mark to tell it the absolute angle of the RA motor relative to a leveled mount (this is why leveling is important). Some mounts don't have optical readers but just a visual one -- typically a simple tick mark on the RA housing; this acts as a rough mechanical index mark. Some mounts don't even have a visual index mark, and you (very roughly) calibrate the RA axis by pointing the counterweight towards ground. Both the latter two makes you manually move the mount to the documented location before powering the mount up -- the power-up position is then taken as the "calibration." (very rough, but with a bubble level or digital inclinometer, can get you within a degree or so).
Finally, there are mounts that don't have any of the above functions, and they require you to use stars to determine the angle of the RA (and DEC motors). This is why these mounts need to be star aligned before the mount is connected to any computer control, the ASIAIR included.
The good part is that alignment using multiple stars can be very accurate. Potentially more accurate than you can level a mount using a bubble level if you use sufficient number of stars. It just take more time and effort and require this setup step after it is dark enough to see multiple stars.
Unless you have a permanent pier and spend multiple nights aligning a permanent mount, a GOTO might only get you close to a star (and perhaps not even get the star in the FOV of the camera). This is where Plate Solving comes in. It measures the true mount location after a GOTO and then make the corrective move.
Note that if the RA axis motor angle is not accurately known, Auto Meridian Flip can also be delayed (by 4 minutes in time per degree of RA position error). Plate Solving will not solve that problem; if late Meridian Flip is a problem, you need to better level your mount (to much better than 1 degree) and also do more than a single star alignment.
Chen
