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How to get Plate Solve Sync working for a 12" Sky-watcher GOTO Dobsonian?

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#1 Ritaelyn

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Posted 18 January 2025 - 11:13 PM

I read someone who has the 14" version uses Sharpcap to plate solve and sync their Sky-watcher Dobsonian for better tracking accuracy and making it so they don't need to do 2-3 star alignments.

I've tried this but it crashes the SynScan ASCOM driver every time I attempt it. I'm only connected to it on a mini PC via wifi and the SynScan Pro app on Windows. When that happens I have to restart Sharpcap completely and restart the windows SynScan pro app completely.

I'm on the latest version off their website. Is there a good last known version that might work with it?

How can I get this sharpcap feature to work?
Thanks!


Edited by Ritaelyn, 19 January 2025 - 05:06 AM.


#2 Ritaelyn

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Posted 19 January 2025 - 05:06 AM

Because there are literally over a dozen combinations to connect a SkyWatcher mount to a computer and do the alignment, please specify which ones you are using.  For example, usb from the hand controller to the computer, with the hand controller doing the alignment.  Right now, it's entirely unclear if the alignment method you are using will let you do that.

I did in the original post. I'm using the windows app, connected over wifi.

There is no USB cable for the mount. I also don't want to connect through the hand controller as reading up on that Sky-Watcher forgot to include a voltage regulator for the hand controller so it's easy to fry and brick this telescope.

 

 

 

The latest version of SynScan Pro app for windows has an automatic alignment routine using plate solving built into it already.  You can just use that instead of having Sharpcap do it, with you slewing around manually and hitting the solve button yourself.

I've tried this. It fails to plate solve :(. I even downloaded the extra .fit files. I have no issues plate solving with Sharpcap's built in plate solver and astap.

 

 

I would suggest you start doing the alignment using SynScan Pro App, rather than the hand controller.

Again - you did not read my post. I'm using the SynScan Pro App on windows, connected over wifi. I'm NOT using the hand controller.

 

 

 

The only thing to watch out for with SharpCap is the limit it imposes on local syncs.  After a certain distance away from the reported position, it won't send the sync.

The whole reason I wrote this post is sharpcap has huge errors sending a sync!



#3 smiller

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Posted 19 January 2025 - 05:08 PM

I have an Orion XT 12G Dob that I use for Astrophotography and although I do not do the sync method like you’re asking, I know of people that do and where they are most active is on the Facebook group “Dobsonian astrophotography”.

 

Also there is one thread somewhere on cloudy nights, possibly the Astro photography beginner forum, where someone was discussing how to this. I will try to find it and update this post if I do.



#4 Ritaelyn

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Posted 20 January 2025 - 06:09 AM

I have an Orion XT 12G Dob that I use for Astrophotography and although I do not do the sync method like you’re asking, I know of people that do and where they are most active is on the Facebook group “Dobsonian astrophotography”.

Also there is one thread somewhere on cloudy nights, possibly the Astro photography beginner forum, where someone was discussing how to this. I will try to find it and update this post if I do.



Awesome thank you! I got into trying astrophotography with my dob after reading your pdf and watching your YouTube lecture.

It's been a frustrating experience as it tends to drift 800+ pixels off target all the time. I've not been able to get it to plate solve and re-center either. Trying to run any goto commands from sharpcap or Nina just crashes it. 😞

Ironically the PC version of Stellarium works perfectly and Stellarium can make it go to targets. Unfortunately the mobile version of stellarium doesn't work.

I've tried everything possible to tighten up the tracking. I put on the correct amount of magnetic counter weights to perfectly level the scope. I've made sure the altitude and azimuth motors are as tight as possible. I've tried turning on and resetting the absolute encoders. Turning those on only made things worse and it would fight with me constantly if I tried to navigate with it. I've also tried various backlash settings. I've tried to add dozens of stars and other sync points with PAE. I've tried setting various backlash values.

The only other thing I've not tried yet is a guide camera. I ordered a player one 48 fps Xena. I'm not too optimistic as I've read somewhere if the mount is sent guiding pulses that it stops tracking for a bit.

I'm out of ideas other than just getting a "proper" mount and a second OTA. it tracks good enough and goto is good enough for visual use. It's just really lacking astrophotography wise. 😞

#5 smiller

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Posted 20 January 2025 - 10:02 AM

This is a real bummer you’re having such issues.  

 

I know people have occasionally ran into various hiccups, but usually the hiccups are from using a new piece of software or new way to drive the telescope.  Typically when someone follows a recipe that had worked in the past, it works for them too, so this is surprising and disappointing.

 

You certainly shouldn’t have gone to the level of all the things that you’ve done, you’ve gone over and above what should be necessary to get basic tracking and decent Astrophotography working. I get great results with just a very simple rough telescope leveling and a basic two star alignment.  All the other measures I do are just to add that little bit extra. Those are just icing on the cake.   So I think it’s not the precision at which you’re doing this there’s something fundamental that we have to find here.

 

You have a very nice set of equipment (nexus and imx571 cameras), this should work very well as it has for many others, so let’s see if we can find the root cause

 

A few clarifying questions:

 

1) For general observation use where you do your two star alignment with a reticle. Does your telescope properly do two star alignment and keep an object in the eyepiece for a good while? (Ex: several minutes at higher power, much longer at lower power)?  In other words is the telescope basically operating correctly out of the box?

 

I wish I had a metric for how long a target typically stays in an eyepiece at a particular power, but I don’t for this type of telescope. But what I’m trying to understand here is when you use the telescope for observation are you getting at least average performance in your Goto and tracking as a typical user gets?  Perhaps you know how yours compares to other people who own your type of telescope with respect to keeping a target in an eyepiece.

 

Also let me tell you that I have sometimes had terrible tracking and I later found I was making a basic mistake. Here are a couple of mistakes I have made and sometimes they’re difficult to sort out when you’re doing this at night:

 

a) I’ve centered it on the incorrect star sometimes with my two star alignment.

b) I put in the wrong date or time accidentally.

c) I accidentally entered East instead of West in my longitude just because I didn’t realize I tapped a button at the wrong time.  This causes a very gross error so it’s probably not this.

d) after traveling with the scope I forgot to reset the location to my new location.

 

 

2) You say it drifts 800 pixels off target after your best alignment, how long does it take to drift that far?  I assume it should drift in an eyepiece just as quickly. (Per question 1).  

 

3) although I use SharpCap sometimes for planetary capture I’m really only familiar with NINA for driving the telescope for deep sky astrophotography (i.e. plate solving and slewing to targets).  So I’m going to focus on getting Nina to work for you and why it may not be working at this time:

 

I think your main problem is that you are not connecting with a physical USB cable through the hand controller to start with.  This is the most reliable method and I know that you’re a bit concerned that the hand controller can break the telescope so the second most reliable way is to use a physical connection to the serial port on your mount with a USB to serial dongle that you can get from Celestron with the synscan app on the pc.

 

It has been often reported that using the Wi-Fi connection is very unreliable so I think this is your issue as you’re starting with the least reliable method to get going.

 

If you’re willing to take some risk using your hand controller, which I think is very low as many people use those Synscan controllers on a variety of systems, you can get going really quickly and reliably using a USB cable from a computer to the hand controller and only the hand controller on your scope.  Then once you get going, you can switch over to the USB to serial cable directly to the mount driven by the PC synscan app and not use the hand controller anymore.


Edited by smiller, 20 January 2025 - 10:35 AM.

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#6 Ritaelyn

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Posted 20 January 2025 - 07:55 PM

You have a very nice set of equipment (nexus and imx571 cameras), this should work very well as it has for many others, so let’s see if we can find the root cause

 

A few clarifying questions:

 

1) For general observation use where you do your two star alignment with a reticle. Does your telescope properly do two star alignment and keep an object in the eyepiece for a good while? (Ex: several minutes at higher power, much longer at lower power)?  In other words is the telescope basically operating correctly out of the box?

 

 

I really appreciate the help! Here is the answers to your questions.

Yes. I've stopped doing eye piece alignments. I have the telescope permanently in the backyard - trying to do astrophotography every night. Using SharpCap's push to assistant which plate solves every frame, usually the alignment stars are within the red crosshairs. Sharpcap reports roughly 0.10 degrees off alignment.

I want to say it stays on target for a good 15-30 minutes. The drifting starts after that. 

 

 

I wish I had a metric for how long a target typically stays in an eyepiece at a particular power, but I don’t for this type of telescope. But what I’m trying to understand here is when you use the telescope for observation are you getting at least average performance in your Goto and tracking as a typical user gets?

For observation it's been fantastic. No complaints here.

 

 

 

a) I’ve centered it on the incorrect star sometimes with my two star alignment.

b) I put in the wrong date or time accidentally.

c) I accidentally entered East instead of West in my longitude just because I didn’t realize I tapped a button at the wrong time.  This causes a very gross error so it’s probably not this.

d) after traveling with the scope I forgot to reset the location to my new location.

I've made all 4 of the above mistakes. One thing I learned is whatever app you have connected to the telescope it resets its location and time to that. So to add on the list of mistakes is one sort of drifting I found was using my iphone app to control it. I'm now only controlling it purely through the mini pc attached to the telescope.

 

I have a NMEA gps dongle that I give it the gps coordinates too, and I put it in the SynScan Pro app.

 

 

2) You say it drifts 800 pixels off target after your best alignment, how long does it take to drift that far?  I assume it should drift in an eyepiece just as quickly. (Per question 1).

I'd say 15-30 minutes in, well after I think I'm fine for the night. The best way to describe it is it feels like its a timeout in the app. If I restart the app I noticed Sidreal is no longer checked sometimes, but not often, like 50/50 that happens. If I recheck sidereal tracking it tracks again perfectly for 15-30 minutes.

 

So I bet that's why you guys have been needing to platesolve and center so much. Since I'm currently unable to with the driver issues - I've had to resort to getting the actual tracking performance as best as I can possibly. 

 

I say the telescope makes for a great EAA experience, just a lousy "go to bed and wake up with photos" experience.

 

 

I think your main problem is that you are not connecting with a physical USB cable through the hand controller to start with.  This is the most reliable method and I know that you’re a bit concerned that the hand controller can break the telescope so the second most reliable way is to use a physical connection to the serial port on your mount with a USB to serial dongle that you can get from Celestron with the synscan app on the pc.

Thank you! I will try this out! Do you have any suggestions on what a reliable cable is, or is that not allowed to make suggestions on the forums?

 

 

It has been often reported that using the Wi-Fi connection is very unreliable so I think this is your issue as you’re starting with the least reliable method to get going.

Yes it is very unreliable. I'm using my mini pc's wifi dongle the best. I also found out that, not documented in the main manual, but in a different pdf on sky-watcher, that the wifi factory resets for an hour of use if you dont have a hand controller plugged in. lol.gif  I solved that wifi stability issue. After I plugged in the hand controller for the wifi - I've not had to reconnect the wifi. However my best insight so far is sidreal tracking gets turned off - like its an internal app or telescope level timeout and I think its the cause of drifting.

So it might be losing wifi and I don't know it - and it might be reconnecting automatically - and thus the loss of sidereal tracking.

 

 

If you’re willing to take some risk using your hand controller, which I think is very low as many people use those Synscan controllers on a variety of systems, you can get going really quickly and reliably using a USB cable from a computer to the hand controller and only the hand controller on your scope.  Then once you get going, you can switch over to the USB to serial cable directly to the mount driven by the PC synscan app and not use the hand controller anymore.

I'm happy to try this and take the risk, and I'll be happy to report back the results. It'll be nice to see if I get better results/stability/etc if Nina and SharpCap is written with the USB to serial cable method.

Thank you sooo much for helping me with this! I hope the USB to serial cable helps! Thank you!


Edited by Ritaelyn, 20 January 2025 - 08:00 PM.


#7 mayhem13

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Posted 20 January 2025 - 10:32 PM

Just a question…..you fellas do disable the auxiliary encoders through the HC settings, yes?



#8 smiller

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Posted 21 January 2025 - 12:00 PM

Just a question…..you fellas do disable the auxiliary encoders through the HC settings, yes?

Yes I turn mine off as the telescope manual says that you’ll get better tracking if they are off.  

 

My tracking is inconsistent enough that it’s hard for me to prove whether it has been better when I turn them off, but my impression is with them off over the last year I have not had as many instances of high drift evenings as I had in the past, but that is anecdotal.


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#9 smiller

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Posted 21 January 2025 - 12:12 PM

 

 

I'd say 15-30 minutes in, well after I think I'm fine for the night. The best way to describe it is it feels like its a timeout in the app. If I restart the app I noticed Sidreal is no longer checked sometimes, but not often, like 50/50 that happens. If I recheck sidereal tracking it tracks again perfectly for 15-30 minutes.

 

So I bet that's why you guys have been needing to platesolve and center so much. Since I'm currently unable to with the driver issues - I've had to resort to getting the actual tracking performance as best as I can possibly. 

 

I say the telescope makes for a great EAA experience, just a lousy "go to bed and wake up with photos" experience.

 

Thank you! I will try this out! Do you have any suggestions on what a reliable cable is, or is that not allowed to make suggestions on the forums?

 

Yes it is very unreliable. I'm using my mini pc's wifi dongle the best. I also found out that, not documented in the main manual, but in a different pdf on sky-watcher, that the wifi factory resets for an hour of use if you dont have a hand controller plugged in. lol.gif  I solved that wifi stability issue. After I plugged in the hand controller for the wifi - I've not had to reconnect the wifi. However my best insight so far is sidreal tracking gets turned off - like its an internal app or telescope level timeout and I think its the cause of drifting.

So it might be losing wifi and I don't know it - and it might be reconnecting automatically - and thus the loss of sidereal tracking.

 

I'm happy to try this and take the risk, and I'll be happy to report back the results. It'll be nice to see if I get better results/stability/etc if Nina and SharpCap is written with the USB to serial cable method.

Thank you sooo much for helping me with this! I hope the USB to serial cable helps! Thank you!

15-30 minutes before a target recentering is typical for this type of telescope.   And so, yes, this is absolutely why we need the “recenter after drift” functionality for all night imaging.  I use Nina to do that.

 

Any USB peripheral cable will work.  
 

If you want the quickest path to success, I recommend:

 

1) Use a wired connection.  My preference is usb to the hand controller as the simplest, but more sophisticated users use USB to a USB-to-serial converter directly to the amount and use the synscan app on their computer.  But I would argue this is more complex and I think you want to start simple and get successful and then move on from there.

 

2) both Nina and SharpCap have methods of recentering after drift, but I’m most familiar with Nina so I would naturally recommend that.  When you get that working it’s pretty easy to have this telescope go all night long. (other than the fact you’ll be fighting dew and a few other side effects of having equipment out all night running unattended).

 

3) Join the Facebook group “Dobsonian Astrophotography” as that group includes a bunch of dedicated Goto Dob Astrophotographers that use both sharpcap and Nina and both methods of physical connection and they can help answer a lot of very specific questions you have.  Nothing better than having two dozen experienced active users to rely on for help.

 

Finally, I did a 1 hour presentation on how I got into doing astrophotography on my Goto Dob on the Astro imaging channel here, it may be useful for you:

 

https://www.youtube....ToGaM__MCbS6wsw
 

And I created a 163 page guidebook on how to do astrophotography on a Synscan Goto Dob and it is here:

 

https://drive.google...4r0IP6PbxA/view
 

Cheers,

 

Steven


Edited by smiller, 21 January 2025 - 12:30 PM.

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#10 Ritaelyn

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Posted 21 January 2025 - 09:46 PM

15-30 minutes before a target recentering is typical for this type of telescope.   And so, yes, this is absolutely why we need the “recenter after drift” functionality for all night imaging.  I use Nina to do that.

 

Any USB peripheral cable will work.  
 

If you want the quickest path to success, I recommend:

 

1) Use a wired connection.  My preference is usb to the hand controller as the simplest, but more sophisticated users use USB to a USB-to-serial converter directly to the amount and use the synscan app on their computer.  But I would argue this is more complex and I think you want to start simple and get successful and then move on from there.

 

2) both Nina and SharpCap have methods of recentering after drift, but I’m most familiar with Nina so I would naturally recommend that.  When you get that working it’s pretty easy to have this telescope go all night long. (other than the fact you’ll be fighting dew and a few other side effects of having equipment out all night running unattended).

 

3) Join the Facebook group “Dobsonian Astrophotography” as that group includes a bunch of dedicated Goto Dob Astrophotographers that use both sharpcap and Nina and both methods of physical connection and they can help answer a lot of very specific questions you have.  Nothing better than having two dozen experienced active users to rely on for help.

 

Finally, I did a 1 hour presentation on how I got into doing astrophotography on my Goto Dob on the Astro imaging channel here, it may be useful for you:

 

https://www.youtube....ToGaM__MCbS6wsw
 

And I created a 163 page guidebook on how to do astrophotography on a Synscan Goto Dob and it is here:

 

https://drive.google...4r0IP6PbxA/view
 

Cheers,

 

Steven

 

Yup as I mentioned before I watched your entire lectuer and read through the entire 163 pdf page above. :)

 

I'm really happy to report that the USB wired connection solved everything! The mount is incredibly responsive with the arrow keys. I was able to have it goto a target in sharpcap! It accepted the sync command just fine! :D :D :D

 

I'm not sure how tracking is on with the wired connection - but at least I can now goto and recenter in sharpcap. I haven't tested Nina yet - but I'm feeling confident Nina will likewise pick it up!

 

I also noticed with the USB connection Nina was able to see the GPS coordinates of the mount. Previously it would report 0,0,0. The usb connection also let me set the mount's altitude. Previously that box was greyed out on wifi and it assumed 0 altitude - sea level, not my altitude. That probably contributed to the poor tracking over time!


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#11 smiller

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Posted 22 January 2025 - 12:10 AM

Excellent it’s working.

 

Yes, Nina will see the coordinates of the mount and if it sees a discrepancy between mount and computer, it’ll ask you which one you want to use.


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#12 mayhem13

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Posted 22 January 2025 - 07:43 AM

Yup as I mentioned before I watched your entire lectuer and read through the entire 163 pdf page above. smile.gif

 

I'm really happy to report that the USB wired connection solved everything! The mount is incredibly responsive with the arrow keys. I was able to have it goto a target in sharpcap! It accepted the sync command just fine! laugh.gif laugh.gif laugh.gif

 

I'm not sure how tracking is on with the wired connection - but at least I can now goto and recenter in sharpcap. I haven't tested Nina yet - but I'm feeling confident Nina will likewise pick it up!

 

I also noticed with the USB connection Nina was able to see the GPS coordinates of the mount. Previously it would report 0,0,0. The usb connection also let me set the mount's altitude. Previously that box was greyed out on wifi and it assumed 0 altitude - sea level, not my altitude. That probably contributed to the poor tracking over time!

Did you connect to the HC or directly to the mount?


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#13 Ritaelyn

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Posted 22 January 2025 - 02:01 PM

Did you connect to the HC or directly to the mount?

Directly to the mount.



#14 smiller

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Posted 22 January 2025 - 02:22 PM

Directly to the mount.

Did you use the SynScan App on a PC?



#15 Ritaelyn

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Posted 22 January 2025 - 02:23 PM

Did you use the SynScan App on a PC?

Yes. :) The latest version too that's from their website by the way. Thank you for all the help you've provided me Steven! 


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#16 Ritaelyn

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Posted 23 January 2025 - 02:53 AM

Did you use the SynScan App on a PC?

FKoiGQm.jpeg

 

I'm having issues with Nina's Slew and Center. Once the telescope starts drifting it spams forever. It's like it ignores the slew.

 

I see all the syncs show up on the app. If I go into the app and slew it very far away then Nina is able to slew it back on target.

 

However if its less than say 1,000 pixels (1125mm focal length) - it seems like the app ignores Nina's slew requests. It just continues to drift drift drift. :(

 

If I go into the app and check no tracking, then re-check Sidereal then it starts working again. That's great if I'm there manually watching it. It's not great for "go to bed and sleep" imaging.

 

I'm getting really frustrated. I'm not sure what to attempt next.

 

I've not tried a sequence yet in sharpcap. Sharpcap has no problems with slewing the mount manually with its GOTO and platesolve.

 

Does anyone have any ideas on how to get Nina and this mount to play nice?

 

I'm getting really frustrated and close to saying **** it and buying a ONTC telescope and a proper equitorial mount. Imaging with a 12" goto dobsonian sounds nice in theory but with the constant drifting that happens 15-20 minutes in I'm getting super frustrated. All this work for images that, quite frankly, with the field rotation and drifting, is refractor-like in quality.


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#17 mayhem13

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Posted 23 January 2025 - 07:45 AM

I'm getting really frustrated and close to saying **** it and buying a ONTC telescope and a proper equitorial mount. Imaging with a 12" goto dobsonian sounds nice in theory but with the constant drifting that happens 15-20 minutes in I'm getting super frustrated. All this work for images that, quite frankly, with the field rotation and drifting, is refractor-like in quality.

I get it……but for the price of automation?…..whew…..a functional EQ set up like that is gonna be a pretty pennie and still not without challenges…..large newts tend to slip collimation when used equatorially where the DOB mirror mounting isn’t challenged. Same goes for the focuser/imaging train with changes in sag. I have a well tuned 10” F4 and a mount that can handle it…..ask me how many times I’ve used it? lol


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#18 smiller

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Posted 23 January 2025 - 10:23 AM

I think what you are experiencing are typical teething pains, and getting a new system going is fairly complex regardless of what type of system you try to set up, whether it’s an equatorial system with guiding or whatever, you will have beginner teething pain.   All these systems have some complexity as you are often stringing together various hardware  and software components and configuring them to make them all work together under a variety of conditions.  Just wait until you get to stacking and proper image processing trying to match what the best can accomplish…. This is simply a complex hobby you’ve chosen.  It’s a long journey for everyone.

 

A common problem with Nina’s center after drift on these scopes is people often set the tolerance too tight. I noticed that it looks like it’s saying that your error is just over one arc minute. That’s 60 arc seconds, and I see that your pixel scale is .69 arc-secs and this means that you have a tolerance of only about 100 pixels, if my math is correct (and it may not be).

 

If that is so, then 100 pixels or 1 arc minute is usually too tight of a tolerance for your type of telescope when it loses into position, it is often wrong by more than that I would set that tolerance to 3x that to start with.  You can always tighten it up later as you learn about your system and how precise it is in slewing.  The setting can be changed in the plate solving tab

 

The reason why it works sometimes and not others is because there’s some inconsistency in how accurate it ends up and that sometimes depends on how big of a slew it’s doing so I think what you’re seeing is just the inconsistency in trying to get to within your tight tolerance.

 

Look on the bright side:  You got plate solving to work and a lot of people get stuck there because they have some entry incorrect: Either their pixel scale is off or their database isn’t downloaded correctly or they don’t let the scope settle enough, or their platesolve exposure isn’t right, or, or…. There are a lot of things that go wrong just getting plate solving to work and you got past that!

 

When I was just getting started, I got stuck on just getting plate solving to work consistently for two full evenings…

 

Don’t give up yet as you’ve made huge progress already!  Just a few days ago you couldn’t even get any of these systems to reliably to connect to your scope, you were using SharpCap and not NINA, and now you have Nina installed, configured, with all the drivers and databases, connected to the scope, platesolving and driving it?   Dude, you’re progressing at a really fast pace!  Now you are just in the stage of working out the bugs in your configuration and setup.


Edited by smiller, 23 January 2025 - 01:31 PM.

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#19 Juggernaut

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Posted 23 January 2025 - 12:39 PM

FKoiGQm.jpeg

 

I'm having issues with Nina's Slew and Center. Once the telescope starts drifting it spams forever. It's like it ignores the slew.

 

I see all the syncs show up on the app. If I go into the app and slew it very far away then Nina is able to slew it back on target.

 

However if its less than say 1,000 pixels (1125mm focal length) - it seems like the app ignores Nina's slew requests. It just continues to drift drift drift. frown.gif

 

If I go into the app and check no tracking, then re-check Sidereal then it starts working again. That's great if I'm there manually watching it. It's not great for "go to bed and sleep" imaging.

 

I'm getting really frustrated. I'm not sure what to attempt next.

 

I've not tried a sequence yet in sharpcap. Sharpcap has no problems with slewing the mount manually with its GOTO and platesolve.

 

Does anyone have any ideas on how to get Nina and this mount to play nice?

 

I'm getting really frustrated and close to saying **** it and buying a ONTC telescope and a proper equitorial mount. Imaging with a 12" goto dobsonian sounds nice in theory but with the constant drifting that happens 15-20 minutes in I'm getting super frustrated. All this work for images that, quite frankly, with the field rotation and drifting, is refractor-like in quality.

You will be able to get it.
It works fine with my 10 inch GoTo. I usually image all night long while I am sleeping most of the time (longest session was 9 hours of unattended imaging).

I am not in front of NINA right now, but there is a setting in the platesolving where you can adjust the amount of error it will accept. I think the default is 1 arcsecond. When that is too low for you setup, it can be below the level of where the scope feels like it needs to move so it won't move and NINA won't be happy. I believe I increased mine to 3 arcseconds and then that lets NINA be happy that you are centered enough and then it continues to image without an issue.

Note that most people are using NINA for this, but sharpcap definitely has been used with success for others as well.

I hope this helps!

 

Let us know if you have any other questions. It works just fine - these are just some growing pains you are having. I didn't think I could get it to work, but I did and it wasn't through any particular magic, but of course attention to details is key.


Edited by Juggernaut, 23 January 2025 - 12:41 PM.

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#20 smiller

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Posted 23 January 2025 - 12:57 PM

You will be able to get it.
It works fine with my 10 inch GoTo. I usually image all night long while I am sleeping most of the time (longest session was 9 hours of unattended imaging).

I am not in front of NINA right now, but there is a setting in the platesolving where you can adjust the amount of error it will accept. I think the default is 1 arcsecond. When that is too low for you setup, it can be below the level of where the scope feels like it needs to move so it won't move and NINA won't be happy. I believe I increased mine to 3 arcseconds and then that lets NINA be happy that you are centered enough and then it continues to image without an issue.
 

+1 on this.

 

Here is the setting in NINA:

 

NINA Pointing tolerance.jpg

 

I have mine set to 4 arcminutes and it works great.

 

For most large slews to a target, it's outside the tolerance and has to try once more to fine tune it.   Every once in a while it has to try again a third time.   For Center-after-drift, a similar thing happens, but sometimes it's right on, sometimes it has to try one more time.


Edited by smiller, 23 January 2025 - 01:31 PM.

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#21 Ritaelyn

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Posted 23 January 2025 - 03:36 PM

+1 on this.

 

Here is the setting in NINA:

 

attachicon.gif NINA Pointing tolerance.jpg

 

I have mine set to 4 arcminutes and it works great.

 

For most large slews to a target, it's outside the tolerance and has to try once more to fine tune it.   Every once in a while it has to try again a third time.   For Center-after-drift, a similar thing happens, but sometimes it's right on, sometimes it has to try one more time.

Thank you! It was set to the 1 arc minute default. I've set it to 4. I'll report back on how well it does tonight. I also copied your gain and bin settings too. Thank you! 


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#22 Ritaelyn

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Posted 24 January 2025 - 11:56 AM

+1 on this.

 

Here is the setting in NINA:

 

attachicon.gif NINA Pointing tolerance.jpg

 

I have mine set to 4 arcminutes and it works great.

 

For most large slews to a target, it's outside the tolerance and has to try once more to fine tune it.   Every once in a while it has to try again a third time.   For Center-after-drift, a similar thing happens, but sometimes it's right on, sometimes it has to try one more time.

Hey Steven!!! This fixed everything!! Thank you!! grin.gif grin.gif grin.gif grin.gif grin.gif

 

In my bortle 8.5 backyard in Vegas it stayed on target on Bode's galaxy for 8-9 hours. Here is what the initial stack looks like from Sharpcap. 

Thank you so much! 

 

GxfWIKO.jpeg


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#23 mayhem13

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Posted 24 January 2025 - 02:40 PM

How are you managing the field rotation?



#24 CowTipton

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Posted 24 January 2025 - 02:53 PM

How are you managing the field rotation?

 

For individual subs? Not necessary as they're very short.  A few seconds.

 

 

Over the entire duration of the shoot?  Without a rotator, you can just crop it down to get rid of the edges where the overlap is apparent after stacking.


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#25 Ritaelyn

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Posted 24 January 2025 - 03:45 PM

How are you managing the field rotation?

 

I'm not. I shot the above image with 12 second subframes. Honestly I think 12s was a bit too long too (sharpness in sharpcap was soft), I might try 8s or 4s. I shot with NINA, and ran sharpcap's folder based stacking in the background.

In the center sharpcap reported green for field rotation of around 1.3~ pixels @ 12s frames, but red on the edges. As you can see over my 8 hour shoot the field rotation made a squarey-circle. Sharpcap used the first frame in black, and the light-polluted purple frame is the stacked result of all the remaining area of the image after field rotation.

I'm trying to figure out stacking in Siril right now - however its not fun given the 2,000+ frames it produced at 52 megabytes each (104 gigabytes of data! lol.gif )

 

I also have a rotator so I could have Nina estimate the original degress of the image - was around 227 degrees going off of memory last night. I could then have a loop of shoot, rotate, shoot, rotate, etc. I happen to have a primalucelab rotator on my dobsonian to test out field de-rotation. Sadly even though this rotator advertises field derotation - they don't have it's capability in the existing PLAY software despite advertising all over it does field derotation. I'm a software engineer myself so I can do the calculations based on the mount's current coordinates and talk to the ASCOM driver of the rotator/etc. 

 

Now that centering is working quickly - the quick and dirty in me is trying a shoot - rotate - shoot first in Nina to see if that de-rotates it "enough." 

 

Field rotation is really weird. On a 1 hour shoot it does hell with the diffraction spikes. 8+ hours in - sigma pixel rejection removed all the diffraction spikes and gave me refractor-like stars with no spikes - heck, I'm surprised it even removed my mirror clip diffraction too. I didn't need to use any apodizing masks to remove diffraction spikes, no anti-egret masks, no lost aperture with mirror clip masks! 

 

Ultimately though field rotation has a huge price to pay - it turned my lovely APS-C style sensor into a 4/3 crop sensor. So if I wanted to do wide sweeping mosiacs with this dob - that's getting rough without solving field de-rotation.

 

Another issue I've found with my rotator is it slightly changed my flats and tilt. So I'm not sure how the calibrated images would look like with it either. Without the rotator with a secure mechanical threaded connection I could mostly re-use flats for an entire week until dust buildup was too much and I had to either A. clean out the dust (which let me keep the same flats - I still took new flats just to be sure, couldn't really tell a difference grin.gif), or B. take new flats.

 

I rotated my camera roughly 2 degrees last night to get the initial diffraction spikes to line up perfectly square with my initial image. That required new flats as that minor change was just bad enough that the images looked really bad on the edges. 

 

So there is huge risk that you might get some garbage calibrated frames with constantly de-rotating on a cheap dob, especially a fast dob where the secondary doesn't even appear as a perfect circle through the focuser (and if its fast enough - it shouldn't appear as a perfect circle when you're collimating it enough.) 

So one might want to make a master flats library for a field derotated image, say 40 frames at each 1 degree rotation, so you're stacking 360 degrees * 40 frames per degree = 14,400 frames going into a master flat. Now imagine having to do that every day due to dust. Yuck. I woudln't do anything less than 10 frames/degree, so 3,600 frames as the bare mininum. 

 

Even worse - that master calibrated file might not work well enough on the edges, and only works on the center. Or even worse - you now have to calibrate with the nearest degree flat, or even worse. Now, imagine trying to figure out what degree flat to use as you could have Nina write out the degrees in the file - that'd roughly be the same number given field de-rotation. You'd have to write your alt-az coordinates in the file name from Nina (is that even possible?) to then have software re-rotate that to pick the correct flat! Even then - what if 1 degree wasn't good enough for a flat? 1/2 degree? 1/10 of a degree? 1 arc-second? grin.gif

 

The last issue is I also have random slippage at times with my Starizona nexus coma corrector & reducer with the rotator. I chose the 2" visual back adapter for my rotator as while the coma reducer has m48 threads on both sides - I've read that some people had to order a collarless version of the coma corrector to get it far enough in the draw tube on some dobs! Thankfully I didn't need a collarless version - but I don't think if I got a m48 adapter on the rotator I will be able to focus. I could absolutely be wrong, but my understanding is the coma corrector needs to grab light inside the draw tube, not outside. Please someone correct me if I'm wrong about this. I might just order the m48 adatper to test it out.

 

Regardless - I don't think it'll change the need to take at least 360 degrees of flats as even if you have a perfectly collimated newtonian (which isn't possible without robotics), I'd think that rotation alone will always require new flats with a newtonian design because of collimation. That's not bad if you're wanting to frame things for a large mosiac on an equitorial newtonian - new flats for a new chosen manual rotation is reasonable.

 

So that also means field de-rotation on a dob means shooting images without a coma corrector - who would want that? Maybe that's fine for planetary and lunar, but Autostakkert already has experimental field-derotation that seems to work for me.

 

 

So yeah, its a fun experiment. So you either capture cheap/fun images with an APS-C sized sensor that gets cropped to 4/3 because of field rotation, or get a wedge for this (not sure how good this would be on a wedge), or you get a proper imaging telescope and a proper equitorial mount.

It rocks for EAA - its really cool to have this fast dob setup. From the comfort of my own home it was showing the horsehead nebula within minutes - despite the light pollution. I can't wait to take it to a bortle 2~ zone!  For less than 5 minutes field rotation isn't really noticeable on an EAA style of setup. The image is rotated 1-2 degrees over that time period.

 

I'd say if you want picture to picture pixel perfect images on your sensor - you'd need to go with a "proper equitorial mount", which I'm still considering doing. The unconventional dob approach was fun, it was a fun puzzle to accomplish this, and it was a great intro to astrophotography for me. :D 


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