Plate Solve & Sync

Discussion of using SharpCap for Deep Sky Imaging
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TimothyTim
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Joined: Fri Jan 25, 2019 12:00 am

Plate Solve & Sync

Post by TimothyTim » Fri Jan 25, 2019 12:04 am

Hello;

I've been having a problem with my Plate Solve and Sync. When I have been using my Refractors 102mm and 80mm, when using the Plate Solve & Sync, SharpCap would send the scope with the target somewhere within the frame, not center, but well within the frame for me to manually adjust.

However, this has changed dramatically once I started using my EdgeHD 925, I updated my index files (using All Sky Plate Solver, which uses Astrometry), when I do the Plate Solve and Sync, it does detect the stars and does it's job, but the object is not within the frame. Usually it's somewhere very near the frame but I would have to spend some time trying to find it.

Any idea the reason behind this and solution?

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admin
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Re: Plate Solve & Sync

Post by admin » Fri Jan 25, 2019 7:53 am

Hi,

I assume that this is a consistent offset – i.e. if you do the solve and sink 2 or 3 times in a row it always ends up at the same position with the target a bit out of view. In that case my suspicion would be on a difference between the coordinate system epoch used by the mount and the plate solving tool.

The plate solving tools supported by SharpCap will give a solution in the J 2000 coordinate system. SharpCap will query the Ascom mount driver to find out what coordinate system it claims to use and if the mount claims to use a JNOW coordinate system, SharpCap will perform the conversion before sending the position to the mount. However if the mount uses JNOW but incorrectly reports that it is using J 2000 then it's possible for an error like the one you see to occur.

Actually, thinking about it this could also occur if there is a mismatch between the coordinate systems of the mount and this guy at the software you are using to do the initial GOTO of the target. If those 2 pieces of software disagree on the coordinate system then the initial pointing position may be wrong and SharpCap may be correctly re-centring on the wrong position if that makes sense.

Hope this helps give you some lines of investigation.

Cheers, Robin

TimothyTim
Posts: 6
Joined: Fri Jan 25, 2019 12:00 am

Re: Plate Solve & Sync

Post by TimothyTim » Sun Jan 27, 2019 9:30 am

Robin;

Yes, that is correct it’s syncing to the same location every time just a bit off the FOV. This wasn’t a major issue when I used 102MM it wasn’t centered but inside the FOV. This is a whole new problem with 9.25.

The mount is Atlas Pro and using EQMOD. I have All Sky Plate Solver which was configured as per your manual. I’ve been doing star hoping to get the objects but it has been a pain.

Any recommendations on how to resolve this and what to check?

cuivenion
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Re: Plate Solve & Sync

Post by cuivenion » Sun Jan 27, 2019 10:49 am

Make sure the epoch is the same in EQMOD and All Sky Plate Solver.

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Re: Plate Solve & Sync

Post by admin » Sun Jan 27, 2019 7:17 pm

Hi,

Yet it is almost certainly going to come down to the epoch not matching somewhere between either your planetarium software, your mount ascom driver, the plate solver and SharpCap.

Hopefully the documentation for your mount Ascom driver will say what epoch it uses. You can also find out the epoch that it reports to SharpCap by capturing a one second framed fits format and looking at the fits meta data for the EQUINOX field. If the mount is reporting J 2000 to SharpCap then the equinox value will be 2000, if it's reporting J now then the equinox value will be 2019.something.

It's also worth looking at the SharpCap log after the plate solver operation as the log will contain the coordinates that the mount claim to be at before the solve, the results of the plates of operation and the resulting go to movement.

The two likely possibilities are

1) your planetarium software is using a different epoch to the mount driver. This means that the original go to the target is going to the an incorrect location due to the epoch mismatch and the plate solve in SharpCap will then take you accurately to the incorrect location

2) your Ascom mount driver is reporting the wrong epoch to SharpCap, meaning that SharpCap is either failing to correct from the J 2000 results from the plates over to the J now epoch required by the mount or incorrectly correcting when in fact the mount once a J 2000 epoch coordinate.

Hope this helps, Robin

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