Meridian Flip - then Re-Flip


Last night I encountered an issue - not for the first time - but it’s happened several times. After imaging for about 2.5 hours, it was time to perform a meridian flip. I got the normal “countdown” and hit the “flip now” option as there was only about 15 seconds before SGP automatically did so.

I watched as SGP went through the regular routine of taking an image, the moving the scope to the other side of the mount. Once there it started its plate solve routine…then, here comes the scope slewing BACK to the side of the mount it had been on. I grabbed the hand control and stopped the slew as I wasn’t sure where the scope would end up. At that point I was just frustrated and shut everything down. Also, there doesn’t appear to be a “graceful way” of exiting or halting SGP when this occurs. The only option on the menu is to “resume sequence” and since the scope is pointing to la-la land, there’s no point in SGP starting to take images immediately,

As stated, this has happened on numerous occasions. Anyone else experience this “feature”?



There could be a zone close to the flip position (usually the meridian) where the mount’s idea of pier side is a bit indeterminate. If you force a flip early the mount thinks that it’s past the flip position so does the flip but the plate solve and sync may cause the mount to think it’s not reached the flip position and so the slew causes the mount to flip back.

The solution is to keep tracking until the mount is sufficiently past the flip zone that there’s no doubt about what side of the meridian it should be on. It’s not possible to say how far that is, it will depend on things such as the mount, the mount errors, particularly cone error, and how it implements sync. If you have enough room I’d be generous, maybe 5 degrees past.

And don’t try to force a flip early.


I hear your points. Problem was that IC410 was almost at zenith and I’ve already had to add a 12" extension to my G11 to prevent camera/tripod crashes in these cases. At that time, it was parallel with the mount and had very little room to play with. I might be able to add a 5-minute delay without a problem, but 5 degrees wouldn’t work, unfortunately.

Perhaps adding a delay for “Auto-center delay after meridian flip” and then I could add plenty of time before an auto-center is triggered? Another option - SGP tracks “Hey, I just slewed FROM that side of the mount - now I’m on the other side - I don’t need to flip back” logic.

Also, when I stop the back-flipping, I can go to my hand controller and issue a GOTO and the mount knows where to slew to find the object. Not sure what the difference is (if any) in the command SGP would issue to the mount for a GOTO.

Just my thoughts.



The difference is the sync that SGP does. This changes the mount model and it looks as if it means that the mount thinks that it hasn’t passed the meridian so the slew command issued after the sync cause the flip back.

I suggested 5 degrees because I typically have 20 degrees to play with but if you haven’t try less. If you are finding that a slew issued a minute or two later is OK then maybe 5 minutes will be enough. Try it.

The error that causes a large difference in position after a flip is the cone error. The difference in position is something like twice the cone error so reducing this may help.

In most cases SGP doesn’t issue explicit flip commands, it waits until the mount thinks it has passed the meridian and issues a normal slew command. The slews used to centre are also normal slews. It’s up to the mount to manage the pointing state. The exception is in the rare case where a mount supports set side of pier, in this case the pier flip is handled by the driver.


We’d need logs to see what’s going on.



Thanks Jared. I’m going to add a few minutes to the flip settings delay and see how that works. If SkyX is correct, that should solve the issue.