PHD reports dithering when it did not happen


So, I was sitting down to process the past weekend’s data when I noticed that none of my images seemed to have been dithered.

Checking the settings in SGP shows that I had somehow managed to uncheck the dithering option. Ok, my fault.

But in PHD, after each image it does report that it was dithering. Even though the data shows that it did not do it. Why did it report do this when dithering was turned off? If I had not seen the dithering line in the PHD graph, I would have realized I needed to turn it on in SGP.

Is this a problem with PHD where it reports that it was dithering when it was not, or did SGP send it some kind of fake signal?


I believe there is an issue in SGP that if dither is unchecked but “Settle at” is specified that SGP will still command a dither. Or it could be that if any autoguider is selected that SGP will command a dither (effectively ignoring the “Dither” option). I can’t recall which, but there is an issue with one of those that will command a dither when you don’t expect it. If you really don’t want to dither then just select “No Auto Guider” for the time being.



You are right, I did have “settle at” enabled, so maybe it did something like command PHD to “dither 0 pixels” which caused the PHD graph to report that it did drizzle.

The real problem is that I did indeed want to dither, but the mixed up options made it look like it did while it did not. Maybe add some kind of reminder that the combination of options may be a mistake? Maybe there is some valid use for that combination of options that I don’t know about.


Presumably this means that while PHD can be running it won’t be controlled by SGP. This will preclude pier flips or changing target won’t it because when the mount is moved the guide star will be lost and PHD won’t know that it needs to select a new guide star.


Maybe. PHD2 is pretty smart if it has an ASCOM connection to the mount. I know it will detect slewing and stop guiding (I don’t know if it will start back up), I’m also not sure how it would handle a pier flip.

I’m not saying this is ideal. I’m saying this is a bug we need to address, but to work around it for the time being you may be able to deselect an auto guider.

I read your initial post wrong. I thought it was dithering but you didn’t want it to. Sounds like we didn’t command a dither but then waited for guiding to settle. That could be valid (but unlikely), I can’t personally think of a reason why that would be a valid use but I’m sure some of our very creative users will prove me wrong :slight_smile: