Polar align error

Using SharpCap's Polar Alignment feature
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Brian
Posts: 2
Joined: Tue Aug 20, 2019 3:47 pm

Polar align error

#1

Post by Brian »

I have a question about the accuracy of Sharpcap versus my handset's Polar Align accuracy.

I have a Celestron11" SCT on an CGX mount. I use a Celestron RACI with a GPCAM2 as the camera for the Sharpcap technique.

I did the folowing. I used Sharpcap to Polar align my mount. I had no issues with the plate solving and everything ran happily. I finished with a polar align error of L 51" and D 4", which I was quite happy with. (I actually got it a lot closer but tightening up the bolts moved the mount a bit.)

Afterwards I ran an align on the handset (6 stars total) and, out of interest, checked what the handset thought the error was. I got an error of AZM -8'32" and ALT -6'25". Which is quite different.

I then repeated the process in reverse. Using the handset All Star Polar Align process I got the error down to AZM -3" and ALT -1'8". I then ran the Sharpcap polar align technique and got an error of R 1'20" and Up 8'17". Which is kind of consistently out the same way. Any ideas which I should trust? Or am I making an error in my Sharpcap technique?

Thanks
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admin
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Re: Polar align error

#2

Post by admin »

Hi,

In general the best way to be sure whether you have good polar alignment or not is to take some long exposure images and see whether the stars trail or not. The proof of the pudding is in the eating and all that…

I used several goto based alignment tools before I added polar alignment SharpCap and I found them all to be pretty unreliable – essentially you can run the same tool again and again making adjustments each time that it suggested and still get results suggesting that you had poor polar alignment. I think the biggest problem with this approach to polar alignment is that if the goto is not perfectly accurate each time then the errors build up in the calculations leading to the alignment suggestion.

It would also be worth you checking out the troubleshooting page for the SharpCap polar alignment just in case you're falling foul of any of the common problems like flex between the guide camera and the mount or a dangling cable.

https://www.sharpcap.co.uk/sharpcap/fea ... leshooting

Cheers, Robin
Brian
Posts: 2
Joined: Tue Aug 20, 2019 3:47 pm

Re: Polar align error

#3

Post by Brian »

Hi,
thanks for the link. I've tested out your suggestions re flexure of the mount/cameras etc and I don't get any issues (the values are a few seconds different). I've found that if I use the alignment procedure on the handset, then check the error using SharpCap, the results are closer than vice versa (which probably means I'm not doing it correctly).

Anyway, there isn't much difference between the tracking on both. I have to guide in either case and it does appear that if I use the handset's polar alignment technique, it positions slightly better so I'll stick with that, which is a shame, as the SharpCap technique is a lot easier.

I should point out that I am actually using the scope in an observatory. You might well ask why don't I do drift alignment. Well,I can fine tune it all I want but after I tighten up the mount, it ruins the alignment so I hoped these techniques would be better. But that's for another thread/forum.

Thanks.
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