Synscan polar alignment

[JamesF]

As I've posted elsewhere, when I do a three-star alignment with my HEQ5 I get elevation and az errors in the region of a small number of minutes. Last night I tried to use the polar alignment feature on the Synscan handset to improve the polar alignment further. I did a three-star alignment on stars as far apart as I could manage, then went through the polar alignment process and repeated the both steps a further three times. Finally I did one more three-star alignment which gave the errors as 0'13" in elevation and 3'13" in azimuth.

When I then tried to find a target (M27 -- within the triangle formed by the alignment stars) the mount was well out, and even ten second exposures showed significant trailing.

I've read the latest manual from the Skywatcher site and I can't see that I've done anything obvious wrong. Anyone have any clues as to why it might not have worked? It's been suggested already that I try two-star alignment instead which is fine, but it would be useful to understand the actual problem too.

James

[DrRobin]

Hi James,

I think the problem is that the scope needs to be polar aligned and then the home position needs to be very accurate, so that the first star of the three point alignment is almost spot on. To do this I do the following:

1) I polar align my EQ6 (will be the same as a HEQ5)

2) Then with the scope in the approximate home position, I select a very bright object (moon or bright star) and slew to this.

3) I then slacken the clutches and centre the object as best as I can without adjusting touching the Synscan. I try to get it spot on and then tighten the clutches. I also align the finder at the same time.

4) I then park the scope.

5) I either switch off or cancel the park and run through the 3 star alignment. If the first star is still a fair way off, I re-slacken the clutches to centre it roughly before making final adjustments with the Synscan keys.

6) I complete the 3 star and at the end it tells me successful.

Targeting objects with the Goto are never far away and it will track un-guided for around 60 - 90 seconds depending on where the object is.

If I don't do this then I usually get 'poor alignment' although it is never far out even on a small FoV and since I use guided shots it doesn't really make that much difference, just finding the object in the first place.

I hope this helps?

Robin

[JamesF]

Thank you, Robin. I can only give it a try and see what happens

James

[dph1nm]

One thing I noticed with 3.32 is that if you choose a different set of 3 stars for the alignment you can get quite different alt & az errors. So it is clearly not a foolproof process. I also got into a situation where the pa alignment process resulted in significant trailing (the mount is in an obs and I know it had a pretty good manual alignment to start with). I tried to iterate on the pa procedure several times (redoing the 3-star alignment each time), but it just got worse (although the offset errors were reported as smaller, even though by eye it was clearly not pointing near the pole!). In the end nothing except a complete power off and restarting the alignment routine, including manual polar alignment using the polar scope, from scratch would fix the issue. I was hoping that 3.35 would be better ...

NigelM

[JamesF]

3.35 is what I'm using, as far as I recall.

James