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Telescope alignment using Stellarium

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#1 JOLinton

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Posted 25 February 2021 - 11:32 AM

I have a Starwatcher AZ mount and have used it with an older version of Stellarium successfully. I have recently upgraded to V 0.20.4 which apparently has something called ASCOM support (what is this and do I need it?). It also has a new dialog window for Telescope control which has some useful buttons such as 'Slew' which enable you to go to a selected object etc. (which occasionally works!) It also has an interesting button labelled 'Sync' but this one does not seem to do anything at all. So my first real question is - what exactly is this button supposed to do? (The latest Stellarium User Guide (which is dated 2016) does not mention this button)



#2 michael8554

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Posted 25 February 2021 - 12:06 PM

If your mount is already working with Stellarium, when you slew to an object, if it's not centred, you can centre with the slew controls.

 

SYNCH will then synchronise the mount's starmap with reality.

 

Other GoTo's in that part of the sky will then be more likely to be centred.

 

ASCOM offers drivers for mounts, cameras, filter wheels, focusers etc, making connecting these much easier as they are all made to a specific framework.


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#3 JOLinton

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Posted 26 February 2021 - 11:10 AM

That's what I thought - but when I click on Sync, nothing actually happens. I expected the reticle to move over the selected object but it stays where it is. Does it have to be within a certain distance already?

 

Dopes anyone know where I can find documentation on the latest version of the telescope control plugin (V 0.4.0)? All the documentation I can find refers to much earlier versions and says nothing about Sync



#4 JOLinton

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Posted 27 February 2021 - 02:07 PM

After several hours of struggle I think I may have answered my own question and what I have discovered may be of interest to others. The following assumes a laptop running Windows 10.

 

First - I have abandoned the dreadful handset which came with my SkyWatcher scope and replaced it with a Lynx Astro USB EQ Direct cable from First Light Optics (cĀ£35). But in order to enable Stellarium to talk to the scope you need to download and install several pieces of software (all free)

 

First connect the EQDirect cable to your computer. The appropriate drivers should install automatically. Go to the Device Manager (press WIN-X); click on Ports (COM & LPT) and check that there is an entry saying USB Serial Port (COM X). Note the number of the COM port which has been assigned.

 

(If, as happened to me, the cable did not install the drivers automatically, you will have to install them. Download them from https://ftdichip.com...s/vcp-drivers/)

 

Now download SynScan Pro (https://skywatcher.c...re/synscan-app/). This is the program which replaces the handset and which converts instructions from Stellarium (i.e. RA/DEC coords) into Alt-Azimuth coords. It is this program which performs the necessary alignment. Run the program and check under Settings that the COM port is correct. Also check that you have selected the right type of mount (AZ or EQ). Press 'Connect' and hopefully you will now be able to slew the telescope and align it on one or more stars. Tell SynScan your location. (I imagine it gets the time from the computer)

 

Now we are setup. Run Stellarium. I will assume that you know or can find out how to add a new telescope and open its cofiguration window. Select the 'External Software or remote computer' option. Under 'Telescope Properties' enter a suitable name for your scope 

Now go back to the telescope dialog and click on 'Connect'. Fingers crossed. it should connect.

 

Now for the alignment procedure. First a bit of basic info. When you carry your scope into the garden and power it up, the telescope could be pointing anywhere and the AZ scales could be reading anything so the first thing to do is to tell SynScan (not Stellarium) where the telescope is pointing. To do this click on Brightest Star alignment. Since we are starting from scratch SynScan will ask for two objects, For example select Betelgeuse and Procyon. Press 'Begin Alignment'. Now use the cursor buttons to center the scope on Betelgeuse. Press the tick. The scope will now slew to the vicinity of Procyon. Center the star and click ok again. Synscan now knows the relationship between AZ coords and RA/DEC coords

 

If you have been watching what happens to the reticle in Stellarium during this process it will probably wander all over the place - but eventually, when the alignment is complete, the reticle will settle in the right place. Presumably, Synscan is telling Stellarium (in RA/DEC coords) where it thinks the scope is pointing all the time and eventually it gets it right. Now you should be able to slew to any object you like using either SynScan or Stellarium. Remember, the link between Stellarium and SynScan is two way and is in RA/DEC coords; communication between SynScan and the telescope is in AZ coords.

 

Well, I hope I have got this right. Let me know if I haven't.

 

I still don't know what the 'Sync' button does though!   


Edited by JOLinton, 28 February 2021 - 11:56 AM.



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