3-star alignment versus SharpCap plate solves /syncs

Discussion of using SharpCap for Deep Sky Imaging
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3-star alignment versus SharpCap plate solves /syncs

Post by Paul » Mon Feb 04, 2019 4:08 am

I have a Skywatcher mount and the normal way to get the scope aligned is to: a) Do Polar Alignment, and then b) Do a 3-star alignment or the equivalent.

It seems that the latest versions of SharpCap can do polar alignment using a finder scope and camera of the appropriate size.

Am I correct in assuming that using SharpCap to perform 3 plate solves, followed by syncs, of appropriately separated stars is more or less the equivalent of doing a "traditional" 3-star alignment? I am now referring to using SharpCap with the main camera of course.


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Re: 3-star alignment versus SharpCap plate solves /syncs

Post by admin » Mon Feb 04, 2019 6:53 pm


I think that actually these have different outcomes. If you press the sync button 3 times in SharpCap then that's equivalent to doing 3 separate one star alignments, which means that only the data from the last sync is being used. A 3 star alignment will build a simplified model of the pointing of the amount to take into account any polar alignment offsets and any cone error that may be present. Of course if your polar alignment is virtually perfect and then you have also corrected for any cone error then the 2 will be very similar in their results.

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Re: 3-star alignment versus SharpCap plate solves /syncs

Post by nexusjeep » Mon Feb 04, 2019 10:02 pm

Hi Robin,
If using EQMOD does the append sync after a plate solve not add it to the points list of EQMOD so if you had 3 point alignment set then after three syncs it would have achieved the same thing as it would have built its map from those three synced points. This is using my Skywatcher EQ6-R + EQDirect cable without the Synscan controller.

Personally I have stopped doing multiple syncs anyway as using the polar align function in Sharpcap I get the Polar values for left /right up/down between 0 and 2 seconds quite easily using the main scope and camera, after which a slew through Stellarium / EQMOD and a plate solve puts me on target for the object I have chosen and as I image one object in an evening it appears to stay aligned perfectly.


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Re: 3-star alignment versus SharpCap plate solves /syncs

Post by TimothyTim » Wed Mar 06, 2019 2:56 am

Three star alignment? What’s that?! I use the Atlas Pro with EQMOD and I haven’t done the star alignment in over a year since I started using plate solving. There is no reason I can come up with to use the Star alignment process once you have plate solving up and running with SharpCap.

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