RA and DEC star alignments don't match

Using SharpCap's Polar Alignment feature
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atacamastar
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Joined: Tue Nov 07, 2017 5:58 pm

RA and DEC star alignments don't match

Post by atacamastar » Wed Mar 14, 2018 6:48 pm

I love the PA tool but am bothered by an apparent discrepancy -- It could be me or my rig -- here goes:

I start with mount CW down, within 5 degrees of NCP - I fire up SC and start PA tool -- it plate solves immediately and requests that I move the mount 90 degrees in Dec - again plate solves immediately and I begin my RA and DEC adjustments -- I get it to say "Excellent" and am very happy-- I then rotate the mount back to CW down and the screen now says PA is "Good" instead of "Excellent" -- see attached -- is this normal or is there something wanky with my mount?

Regards,

Tom
RA 90.jpg
RA 90.jpg (213.72 KiB) Viewed 249 times
RA 0.jpg
RA 0.jpg (213.75 KiB) Viewed 249 times

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admin
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Re: RA and DEC star alignments don't match

Post by admin » Wed Mar 14, 2018 9:01 pm

Hi,

you could have a little flex in the mounting of your guide scope causing it to shift slightly as you rotate. A better test would be to re-run the whole PA procedure starting in the 90 degree position that you finished the first run in and going back to home.

There are some good hints on troubleshooting polar alignment issues here - http://www.sharpcap.co.uk/sharpcap/feat ... leshooting

cheers,

Robin

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admin
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Re: RA and DEC star alignments don't match

Post by admin » Wed Mar 14, 2018 9:03 pm

Btw,

what I should have also said is that anything under 1 minute of arc is probably good enough for all reasonable uses. If you have not turned on the refraction correction then the error introduced by ignoring that is ~1 minute of arc or so at 50N and more at lower latitudes. So, the best answer might be to not worry about the last few arc seconds! :)

cheers,

Robin

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