SharpCap Forums

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?

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

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?

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

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

I am facing the exact issue, hope I can get some help here.

I have been using Cates du Ciel Skychart for many years, with Astrophysics mount and a few softwares (including Sharpcap platesolver) without any issue.
Recently I also use Celestron AVX (celestron ascom driver), but often Sharpcap "solve and re-sync" ends up at a wrong location (I repeat "solve and re-sync" it always ends up at same but wrong location).

Do you know whether Celestron ascom driver is reporting the wrong epoc used?

Hi,

the first thing to check is the size of the error - the error caused by having the ASCOM driver incorrectly report J2000 will be up to about 8 minutes of arc (depends on the part of the sky you are looking at, but as of 2024, 8 is the maximum - by 2034 it will have increased to nearly 12 minutes of arc). If you are seeing bigger errors than that then it's not the problem with the ASCOM driver epoch... Or at least that's not the only problem!

The next thing to do is to perform a GOTO from the 'Goto Catalog/Target Co-ordinates' tool in the tools menu - just pick any target above the horizon and let the GOTO run. After it has finished check the log. If you see a line like this
then it tells you that your mount ASCOM driver is reporting JNOW (since SharpCap is converting the J2000 position from the catalog into JNOW before sending it to the mount).

cheers,

Robin

Yes I think it was much more than 8', because my FOV was 20x30 and it was outside.

And what else could contribute to the large error?

Hi,

there are lots of causes that might lead to an initial large error (polar alignment, mount alignment, cone error, etc), but hitting the problem after the plate solving correction has tried to put the target into view is less easy to work out.

If you are trying to image near the celestial pole and the initial GOTO is significantly out then the correction may be off due to the curvature of the co-ordinate space around the pole, but that probably won't be significant unless you are polewards of about +/- 75 to 80 degrees declination.

Plate solving results can sometimes be wrong due to a random error, but that wouldn't repeat again and again.

Mount backlash could be an issue if it is very large, but normally the mount will approach a GOTO target from a consistent direction to avoid this.

Your mount could be rejecting/ignoring the sync command that SharpCap is sending it - try changing the 'After solving ...' setting in the plate solving settings from 'Sync mount and re-center...' to 'Offset the mount position...' which can fix this issue.

To dig into this further, it might be best to send me the SharpCap log captured after you have tried to get things working and had an issue - that will contain the information about the target you chose, the plate solving results calculated at the end of the initial GOTO and the new co-ordinates that were then selected. Addditionally save an image of where the telescope ends up and do a 'plate solve only' there which will show the co-ordinates that you ended up with.

cheers,

Robin