Plate solving ok; sync doesn't work properly

[ippiu]

Meade lx90.

Plate solve works with no problem, as you can see.

Immagine.jpg (135.28 KiB) Viewed 2921 times

But when i sync the mount or sync and recenter it, the coordinates change. And they always change by an offset between 0,23 and 0,28 degree...

2_.jpg (114.69 KiB) Viewed 2921 times

I suspect that this amount of offset is due to a coordinate conversion, from J2000 to Jnow, when apply sync to the mount..

I tried with meade generic driver and meade classic and autostar I driver. Problem persists.
Tried with different plate solvers: either ASPS and ANSVR. Nothing changed. Problem still here.

Thanks for your help

[admin]

Hi,

The plate solving tool always works in J 2000 coordinates. The Ascom driver for the mount should be able to report the coordinate system that it uses (usually J 2000 or J NOW). SharpCap will ask the Ascom driver which coordinate system it uses and if it reports J NOW then SharpCap will perform the conversion before sending the synchronisation command. However, if the Ascom driver uses J NOW but reports J 2000 (or the other way round) then you would get this sort of problem with offset.

The easiest way to work out what coordinate system your mount claims to use is to save a single frame from SharpCap into FITS format. Once you've done that, open the file with a program like FITS Liberator and look at the headers. SharpCap will write an EQUINOX header which will either have the value of 2000 for a J 2000 mount driver or the current date a J NOW mount driver.

Some Ascom drivers may have settings that allow you to configure the coordinate system used, which may help. Currently there is no way in SharpCap to override the coordinate system that the mount reports.

Hope this helps, Robin

[ippiu]

Thanks Robin.

So my meade mount claims to use JNOW? Under equinox It reports 2020.00273224044...

So what happens exactly during sync?

Immagine.jpg (129.11 KiB) Viewed 2892 times

[admin]

Hi,

Okay, the procedure is something like this

SharpCap asks the mount for its current pointing position (which may be JNOW or J 2000 – we don't care)
Image frame is captured and passed to the plate solving engine
the plate solver calculates the position of the centre of frame in J 2000 coordinates
SharpCap converts the J 2000 coordinates to J NOW coordinates based on the Mount reporting J NOW as its coordinate system
SharpCap sends a synchronisation command to the Mount based on the JNOW coordinates
SharpCap issues ago to to the coordinates that the Mount reported pointing to initially

Hope that makes sense, Robin

[ippiu]

Hi,

Okay, the procedure is something like this

1) SharpCap asks the mount for its current pointing position (which may be JNOW or J 2000 – we don't care)
2) Image frame is captured and passed to the plate solving engine
3) the plate solver calculates the position of the centre of frame in J 2000 coordinates
4) SharpCap converts the J 2000 coordinates to J NOW coordinates based on the Mount reporting J NOW as its coordinate system
5) SharpCap sends a synchronisation command to the Mount based on the JNOW coordinates
6) SharpCap issues ago to to the coordinates that the Mount reported pointing to initially

Hope that makes sense, Robin

So my mount says to SC to be in JNOW coordinate, but in reality is it in J2000? But during all this process, where is the coordinate conversion error? During 4 and 5? I edited your message with number at the beginning of each sentence, to understand where could be the coordinate error conversion problem...

[BlackWikkett]

Not sure if this will help but when I had this error with Astrotortilla I did the following and have had no issues since. In my case I used JNOW but I'm guessing if everything was was set for J2000 it would also work. It's worth a shot giving it a try. Seems like if all the software is playing from the same sheet music there will be no conversion needed?

1. Setup Stellarium for JNOW
2. Setup iOptron mount for JNOW
3. Using the Astrotortilla interface, run stand alone outside of SharpCap, setup for JNOW

I've helped one other user following this same procedure that before had incorrect slews after solve and sync. Their plate solving is now working as intended.

Hope this helps, Chris

[ippiu]

BlackWikkett thanks for your suggestion.

1) I don't need and don't use any planetarium software. Why should i use stellarium?
2) I repeat that Meade Autostar 497 (that is present on Meade LX90) hasn't any sort of coordinate setting (i also installed a 3rd party pacthed firmware: it hasn't too that setting)
3) I tried to change coordinate settings in All Sky Plate Solver and ANVSR: put J2000 or JNOW doesn't matter, the error persist.

[BlackWikkett]

I know we're not using same software / hardware except for SharpCap. Just giving example of what I did with my setup when I encountered the same offset as you're experiencing when the plate solver found a solution and the subsequent slew and sync was off.

-Chris

[AndrewP]

Hi,

I have the same set up and have experienced the same issue. Was a solution found to this problem?

Thanks