Re: Apparent loss of tracking after dither command

Dale Ghent

Assuming that the screenshot you provided was taken right after the erroneous event, the reason why guiding stopped in plainly-stated: Something external to PHD2 commanded the mount to slew while PHD2 was still guiding. In such a case, PHD2 will stop guiding and post a complaint.

You mentioned that you turned dithering on in SGP. Dithering is an operation that's normally handled by PHD2 - the sequencing application pauses between exposures, and through its direct connection to PHD2, orders PHD2 to begin a dither operation using either the provided parameters or PHD2's defaults. PHD2 executes this by sending pulse guide commands to the mount to move the field of view a few pixels in a random direction, then reacquires the guide star and resumes guiding. The sequence application observes through its direct connection to PHD2 that the dither op is completed, then starts the next exposure.

I don't know if this option is in SGP, but there is a "manual dither" feature that's common in sequencing apps, typically employed when there is no guide camera and no guiding app such as PHD2 operating, such as with an unguided setup. In such a case, it is the sequence application that tells the mount to move a little to effect the dither. Could it be that you have this feature on in SGP, and thus SGP is not coordinating the dithers through PHD2 at all? If this were the case, PHD2 would then see the guide star and mount move unexpectedly and produce the error you see in the screenshot you provided. This could be one possible explanation.

You didn't explain if you have had previous dither operations execute and succeed during your sequence. Doing your first dither 18 shots into a sequence is pretty late in the game to start doing it as, like I said, one normally sets up dithering to happen every 1-5 shots and no less frequent than that.

I would take Brian's advice and take this up on either the PHD2 or SGP forums.

On Feb 24, 2020, at 12:35 PM, Peter Bresler via Groups.Io <> wrote:

There were problems with retaining the guide scar, although guiding had been working for quite a while. In any case I expect that the mount would keep tracking, but that did fail. When I turned off dither and recentered with a plate solve things were ok.

<guiding 2_23.jpg>

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