Hi guys (and anyone else watching the meridian flip saga),
As I found out from last nights experiments, one other thing to check if your Meridian Flip is really late (other than being "one hour Daylight Saving Time" late) is your tripod's east-west level.
There are people who tell you that leveling the tripod is not important if you do a good polar alignment and use plate solving to GOTO. These smart ones forget the details (dot the i's and cross the t's :-).
Polar alignment will get the RA axis pointed at the pole, so that the mount can track without a declination drift. However, we live in a 3 dimensional world. There is a third axis.
Imagine looking up in the sky and searching for Polaris (near enough to the pole to use as a casual example). You pan the eyes east-west and then north-south to look for it (this is like what polar alignment does). Lets say you have it centered in your view. And you think you are done.
Nope.
Notice that you can tilt you head, while Polaris is centered in your view, and the sky now revolves around Polaris, just like the pretty circumpolar time lapse photos. All the while your head remains "polar aligned" with Polaris at the center.
Why does this matter? Aha, tilting your head is changing the reference point of your head's Hour Angle: it determines the time a star crosses the Meridian in your head!
Having a tripod that is not level in the east-west direction is basically like tilting your head. The time a star crosses Meridian is now different.
What is more interesting is that this time offset will be different with the OTA on the east of the pier and with the OTA on the west of the pier (a Meridian Flip changes the RA motor angle by 180 degree).
Sync-to-mount after a Plate Solve might resolve this problem on your mount, it did not on mine.
How do you check? Obviously, you can do that with a bubble level or a digital inclinometer. But consider the precision... A 1 degree error is very small, right? But that can be enough (if the sign of the angle makes the mount's meridian appear later than the sky's meridian) to delay the Auto Meridian Flip (i.e., the mount does not think that the star has gone past yet). 1 degree of tilt corresponds to 4 minutes worth of time. That said, a $30 digital inclinometer can probably get you to no more than one extra try (1 minute of time) of the auto meridian flip. I.e., good enough unless you are OCD like me (most engineers are, even in retirement :-). I have a couple of the iGaging brand digital inclinometer from Amazon that I have been using for years now; the second one was bought because it had backlight and USB recharging; the first one needed a flashlight to use at night.
How to measure more accurately? ASIAIR has the plate solving tool :-). Once you think you are "star aligned," i.e., the mount knows its RA, do a GOTO to some place in the sky whose coordinates you define to ASIAIR (could just be a named star, if you can find a convenient one). Now do a plate solve. Compare the RA of the plate to the RA that you have asked ASIAIR to go to. Now do a GOTO to a star on a different side of the Meridian (go Home first, just so there is no bias). Check the RA offsets. If they are different, your mount is probably not level in the east-west direction.
Hopefully, this gives a bit more understanding of the late and missing Meridian Flips. Note that in this case, it is not an ASIAIR bug. ASIAIR is is simply depending on the mount to do the Meridian Flip. If ASIAIR were to do its own meridian flip, then the delay will not be there.
I found this out last night when my Auto Meridian Flips were delayed by 5 cycles of AMF retries. ASIAIR kept sending a GOTO to the mount, and the mount thinks it is still on the correct side of the pier and won't move; until the star finally crossed the mount's internal Meridian line. Turns out my mount was well calibrated (almost zero RA error) with a star on the west, but some 4 minutes of RA off for a star on the east, and I was testing with the east-to-west Meridian crossing so time on the east was all important (ASIAIR cannot do West to East meridian crossing anyway right now, ha ha).
Checking with the iGaging inclinometer resting on my dovetail clamp in daylight this morning, I find that the mount is some 1º off level in the east-west direction.
Self inflicted wound :-).
Chen
P.S., for people who are missing the West-to-East auto Meridian flips, notice that even though ASIAIR v1.5 does not know it exists, your mount does. Once the star has reached Meridian, you mount's Meridian Limit should stop tracking. At that point, manually stop autoguiding (or guiding will go bananas) and pause AutoRun. Give it an extra minute and send the mount a GOTO. If it does not flip, repeat with another GOTO a little later. Sooner or later (when the target crosses the mount's meridian), the mount will flip. That manual GOTO should also turn tracking back on (for most mounts) and you just need to turn guiding back on and resume AutoRun.
I started a different thread here on one reason why tracking seems to stop by itself for some people. As I explained in that post, I think it is because the mount has read the west-to-east Meridian Limit and therefore stopped tracking. Since ASIAIR does not think there is a Meridian there, it keeps autoguiding, and you know what happens when you try to auto-guide when tracking has stopped. You can actually successfully auto-guide with no tracking, if the guide rate can be set to above 1x -- but ASIAIR don't let you choose a lava over 0.9x.
