Rotation in the 3rd stage of polar alignment

[Astrodrawn]

Hi,

I have been trying to use the polar aligning feature in SharpCap pro with my Star adventurer 2i, although when I go to the 2nd stage of alignment, the stars drift horizontally to the pole. In the third plate solving image, the stars drift even more dramatically than the 2nd stage, causing SharpCap to give rotation errors. No matter what I try to do, I cannot figure out what is wrong with my setup. I have seen that the Star Adventurer is tracking and I'm using the wifi on the mount to connect it directly to the computer (which seems to work). At the moment I've got no leads on what I could try, so anything will be helpful.

Thanks,
Astrodrawn.

[admin]

Hi,

I have had a look at your log and I can see the drift in the data, happening over quite a short amount of time - 30s to 1 minute.

The rotation of the earth is not going to have any significant effect over that sort of timescale with the setup you are using with your ASI120MM and a relatively short focal length lens.

The fact that the stars aren't going to be moving leaves two main possibilities left

1) The mount is somehow slewing slowly - I think this is unlikely but worth being sure (turn the mount off and see if the movement continues or not)

2) Something is slipping/settling/sagging, meaning that the direction the camera/telescope is pointing in is changing.

Things to check for the second option include

* physical connection from the telescope/guide scope back to the mount
* How the camera is connected into the telescope/guide scope - is it firmly connected and can it be moved?
* Hanging cables that may be pulling on the end of the camera (unlikely to cause an effect this big)
* The clutches of the mount slipping, alowing the axes to turn
* The altitude or azimuth adjustments moving
* The tripod itself sinking or tipping slowly (perhaps if standing on soft ground)

Hopefully you will be able to identify and cure the cause of the drift and then be able to get good results. Unfortunately, since I haven't used the Star adventurer device, I can't give specific advice on what might cause it to slip/drift.

cheers,

Robin

[Astrodrawn]

Hi,

I had a night of imaging and have got the same issues as before, although what was different is that one of my tries at getting the polar alignment feature to work allowed me to properly polar align for me to get an almost sharp photo. I looked at all the connections, etc and I saw none that was causing the rotation problem. I turned off the tracking and then back on again and it seems as though the mount is tracking either too fast or too slow by looking at the star movements. This is weird though, since it is able to perfectly track when I was normally trying to take a photo. I hope there isn't an issue with my tracker motor or something like that, but I don't think there is considering what happened. The logs should say what happened in the run I was able to get it to work, since I am not so sure on how I exactly did it.

Thanks,
Astrodrawn.

[admin]

Hi,

well, that log didn't seem to have the constant drift in the solve co-ordinates during the periods when SharpCap was waiting for you to move on to the next stage, so I think something must have been working better. It's perfectly OK to run the polar alignment with tracking turned off - you are always looking very close to the pole and the procedure takes just a minute or two, so the effect of the earth's rotation will not be noticeable.

I'm afraid I can't be much help with the tracking issue with your mount. I would just check that it knows it is in the southern hemisphere though, otherwise it might try to track in the wrong direction (I think).

cheers,

Robin

[Astrodrawn]

Hi,

I will try doing that with no tracking and will see if I still get the rotation error, if I do then it would probably be cable snags, Dec movements, etc. Weird how it suddenly worked though, I will have to go through the Green Swamp Sever settings to see if there's anything that could be affecting tracking.

Thanks,
Astrodrawn.