Asiair : Target drift due to dithering - Forums

Topic starter

Oct 7, 2022

I have the problem that in the course of the session my target drifts further and further away, the direction is quite different, one night for example down to the left, then up to the right, etc.

I have added a few screenshots, in the first picture the start and in the second picture the target after 5 hours, where it has drifted downwards. Also a picture of the Sky Atlas where you can also see how the target has drifted away.

I also had the problem with the current Asiair version and now hoped that with the test beta version 2.0 it might be fixed, but unfortunately not.
Polar alignment is very good, mount is AZEQ6, Newton 8"F5, guidescope 240mm, guiding is fine, so what is the problem?

I have also tried to see if it could be the balance, I have balanced the telescope completely and with a little overweight in the east, but it doesn't change anything, the drift when dithering remains, it is the same with an130mm guidescope, I am slowly at a total loss...

I don't think it's the setup, because before I used the MGEN3 for guiding and dithering and I never had this problem.

Has anyone else had the same problems?

THX Sascha

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andrea tasselli

Frequent contributor

Oct 7, 2022

The problem isn't a problem at all if the lights are stacked up correctly. But, assuming that it is a problem for whatever reason, then you should set up PHD2 to follow a spiral during dithering and that should take the issue away, if there are no underlying mechanical issues.

Mike Cranfield

Oct 7, 2022

andrea tasselli:
The problem isn't a problem at all if the lights are stacked up correctly. But, assuming that it is a problem for whatever reason, then you should set up PHD2 to follow a spiral during dithering and that should take the issue away, if there are no underlying mechanical issues.

Unfortunately the ASIAir does not give access to the full PHD2 functionality so this is not, so far as I know, available. I have the same problem, I end up doing a periodic GoTo to re-establish the framing. Obviously that is not possible if you leave unattended overnight. As a related issue sometimes, when left overnight, I find clouds can come in for, say an hour or so, then it clears but because the guiding has been thrown out by the clouds the framing is quite far out. It would be great if ZWO could build in something to combat these issues - for example, I use an hourly re-focus setting, perhaps an hourly "re-GoTo" function would help. I think we - and hopefully any other interested people - should leave a suggestion on the ZWO forum. I think they are quite good at listening to customer feedback.

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Sascha Ebeler

Topic starter

Oct 7, 2022 · Edited: Oct 7, 2022

Mike Cranfield:
andrea tasselli:
The problem isn't a problem at all if the lights are stacked up correctly. But, assuming that it is a problem for whatever reason, then you should set up PHD2 to follow a spiral during dithering and that should take the issue away, if there are no underlying mechanical issues.

Unfortunately the ASIAir does not give access to the full PHD2 functionality so this is not, so far as I know, available. I have the same problem, I end up doing a periodic GoTo to re-establish the framing. Obviously that is not possible if you leave unattended overnight. As a related issue sometimes, when left overnight, I find clouds can come in for, say an hour or so, then it clears but because the guiding has been thrown out by the clouds the framing is quite far out. It would be great if ZWO could build in something to combat these issues - for example, I use an hourly re-focus setting, perhaps an hourly "re-GoTo" function would help. I think we - and hopefully any other interested people - should leave a suggestion on the
ZWO forum. I think they are quite good at listening to customer feedback.

Thank you very much, yes i also posted it in the zwo user forum and also uploaded a log, i guess if it can't be solved then i also hope for an auto centre after x hours

Andy Wray

Oct 7, 2022 · Edited: Oct 7, 2022

Sascha Ebeler:
Thank you very much, yes i also posted it in the zwo user forum and also uploaded a log, i guess if it can't be solved then i also hope for an auto centre after x hours

Just in case you ever think about moving off the ASIAir to something like NINA:

NINA has a [Center After Drift] function that would take care of any drift (including those caused by passing clouds etc..)

FWIW though: that isn't a very big drift and I personally wouldn't worry about it too much as it's not really impacting the target you were capturing.

Mark Abbott

Oct 7, 2022

I recently started dithering with an EQ6R Pro mount and ASIAir Pro and noticed the same thing. I did reduce the number of pixels moved during dithering in the settings and that helped some.

The ASIAir has really helped me get started in AP, and it keeps improving, but it does seem to have it's limitations

Sascha Ebeler

Topic starter

Oct 7, 2022

Mark Abbott:
I recently started dithering with an EQ6R Pro mount and ASIAir Pro and noticed the same thing. I did reduce the number of pixels moved during dithering in the settings and that helped some.

The ASIAir has really helped me get started in AP, and it keeps improving, but it does seem to have it's limitations

I have already reduced the pixels to 2, but the drift is much stronger with 5 or 10. I really hope that ZWO will find a solution for this in the future.

Mike Cranfield

Oct 7, 2022

Sascha Ebeler:
Mike Cranfield:
andrea tasselli:
The problem isn't a problem at all if the lights are stacked up correctly. But, assuming that it is a problem for whatever reason, then you should set up PHD2 to follow a spiral during dithering and that should take the issue away, if there are no underlying mechanical issues.

Unfortunately the ASIAir does not give access to the full PHD2 functionality so this is not, so far as I know, available. I have the same problem, I end up doing a periodic GoTo to re-establish the framing. Obviously that is not possible if you leave unattended overnight. As a related issue sometimes, when left overnight, I find clouds can come in for, say an hour or so, then it clears but because the guiding has been thrown out by the clouds the framing is quite far out. It would be great if ZWO could build in something to combat these issues - for example, I use an hourly re-focus setting, perhaps an hourly "re-GoTo" function would help. I think we - and hopefully any other interested people - should leave a suggestion on the
ZWO forum. I think they are quite good at listening to customer feedback.

Thank you very much, yes i also posted it in the zwo user forum and also uploaded a log, i guess if it can't be solved then i also hope for an auto centre after x hours

I have just added support to your ZWO post - looks like they are listening!

Mark Abbott

Oct 7, 2022

I added support in the ZWO forum for this issue too.

Well Written

Freestar8n

Oct 8, 2022

I think that some dithering algorithms are purely random and each move is independent of the previous one - and if so that is guaranteed to wander off in a random walk. But it is simple to keep the dither pattern anchored by effectively subtracting off the previous move that was made. There is no need to keep track of all moves or something. The first move is dx1, dy1 - and the next one is dx2-dx1, dy2-dy1, where all the dx, dy's are some kind of random move with some range of radii. You always know where you currently are relative to the anchor point - and the next move should subtract that off.

If the motion is based on movement relative to a guidestar - it should never wander.

It's a trivial change to the dithering code and I don't know why everyone wouldn't do it this way. MetaGuide dithers in this manner with a Gaussian distribution around the star to keep the moves random while also keeping them relatively short. I would not use a structured pattern like a spiral.

Frank

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kuechlew

Oct 8, 2022

The main question with this respect is whether ZWO bought the rights to change the code of PHD2. It doesn't help if the change is easy if you're not allowed to implement the changes. I'm actually surprised about this behavior of ASIAIR guiding. Never experienced anything like this with PHD2 in "random" mode when dithering.

Clear skies
Wolfgang