Direct Mount Guide dithering while imaging

I usually do five-minute exposures, and while watching the sequence of events, I always noticed that SGP seems to start integrating, and THEN PHD2 shows that it’s dithering. It never really affected my images that I could tell, because of the relative time. I thought maybe it was not a real thing.

Last night I did a stack of 10-second exposures on comet NEOWISE using Direct Mount Guiding. Looking at the raw captures today I see that indeed the integration has started before the dither was performed!

Here’s a link to ten raw FITS files. They’re quite interesting to see how the dithering occurs.

I understand that perhaps the commands to the mount are given before the integration starts, and I guess there is a way to add some delay time.

But why would that not be a default setting? It’s discouraging to discover the problem this way, and lose what might be an only opportunity.


Dither absolutely does not occur during a frame. Direct Mount Dithering can be a little touchy as SGP has 0 feedback from your mount about when it’s done. So basically SGP issues the command, waits for the duration of the dither, waits for the duration of the “Settle at X for Y Seconds”, waits for the duration of the “Mount Settle”, and then begins the process for the next frame.

It sounds like you likely have all of the settle times set to 0 or near 0 or some value that is not adequate for your mount to settle in that time span. With PHD2 we get lots of confirmation that the settling has completed and that you’re within your desired parameters before moving on…but with the direct mount option you have to provide adequate timeouts to allow your mount to stop moving.


I get that, and I understand.

What I’m really asking is that these values have some different installation defaults than zero. When I first try these things out, I’m too ignorant of the underlying problems. They only raise their head after a minor disaster (like those sample comet frames).