ASIAIR does not really do a Meridian Flip -- it depends on the mount to do it.
From what I observed with the ASIAIR, what happens is this:
a) ASIAIR waits for the mount to reach Meridian. When I did the experiment, it actually waited 30 seconds after the object has passed Meridian -- and this is where there are potential problems if the Meridian Limit on your mount is not set up for ASIAIR.
b) ASIAIR turns the mount tracking off. No exposure is made from this point on.
c) ASIAIR starts a countdown (about 250 seconds, if memory serves).
d) when the countdown is done, ASIAIR sends a GOTO to the mount. *This* is what causes the mount to execute a Meridian flip.
The mount is asked to GOTO the same RA,DEC location as the location before the tracking was turned off. However, at this point, the object is on the West side of the Meridian while the OTA of the German mount is still on the West side of the pier -- this condition causes the mount to execute a Meridian flip.
e) with most mounts, the GOTO will also restart tracking again.
f) in addition, ASIAIR also compares the plate center before tracking is turned off with the plate center after the GOTO (and meridian flip) has finished, and tries to center the object better in a sequence of plate solves and GOTOs. This is needed if Polar Alignment is not perfect, or when your optical axis in not perfectly orthogonal to the DEC axis, or your RA axis is not orthogonal to the DEC axis (what is commonly called "cone error").
Note that in step (a), ASIAIR does not stop tracking until after the Meridian is reached. If you had set your Meridian Limit of your mount to 0º , the mount will stop tracking before the ASIAIR stops tracking. Step (f) will then be incorrect. The same problem can also occur if the Local Sidereal Time of your Mount and the same time in ASIAIR are not in agreement.
To avoid the problem, I have set the Meridian Limit of my mount (RainbowAstro RST-135) to 2º (about 8 minutes in time) so that ASIAIR will stop the tracking before the mount reaches its Meridian limit.
Chen
