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Initial alignment using sharpcap?

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#1 ex-Bubblehead

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Posted 13 July 2021 - 10:10 PM

So I just about have everything there, but I need a little advice to overcome a last basic technical hurdle until I can actually start up the EAA learning curve.

 

I have sharpcap talking to my mount (AZEQ5 in AltAz mode) and camera.  I can platesolve within sharpcap using ASTAP.  Is there any way to use that plate solving to perform an initial alignment?

 

The overall flow I am trying to achieve is that I move the scope and mount out of the garage and drop them on the driveway, attach all of the cables and power supplies, turn on the mount, start sharpcap/stellarium, do an initial platesolve to orient the mount, then I'm off to the races.

 

During the hour break in the clouds I had tonight, I was pointing at Polaris and able to get a reasonable solution, but could not get the sync to take.  The closest I got was by moving the telescope to a particular position such that on resetting the encoders in the EQASCOM window in the PARK section, I could move the scope back to Polaris and get close enough for the platesolve sync to take.  The one time I was able to get that to work, however, sharpcap then drove the scope to 180 degrees out in azimuth and claimed it was now pointing north (stellarium showed the same picture, as did the raw data from EQASCOM, they both thought the scope was pointing north when it was roughly pointing south).

 

I'm trying to avoid having to use the HC or the synscan pro app to do a manual alignment.  Is the solution to just do one of the manual alignments, park the scope, then try to match that position the next time I move everything around?


Edited by ex-Bubblehead, 13 July 2021 - 10:11 PM.


#2 alphatripleplus

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Posted 14 July 2021 - 07:23 AM

I use SharpCap 3.2 with ASTAP on my german equatiorial mount (Mach 1) for initial and all subsequent alignments and so it can be done. However, I believe SharpCap is configured to assume a maximum alignment error in any GOTO of 15 degrees when platesolving, and so your initial goto must be within that accuracy for a successful initial sync-and-centre via ASTAP. If you use ASTAP as a standalone, you can configure the maximum alignment error for platesolving as well as other parameters. I don't know if SharpCap 4.0 allows more configuration of ASTAP parameters than vs3.2.



#3 Jeff Lee

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Posted 14 July 2021 - 08:45 AM

 You could try this (I use the StarSense control and have a different way of setting up (camera is on other scope)):

 

1. Plug into the USB connection, Setup your mount/scope to north and level. Manually (either with scope control in Stellarium or SharpCap ) move to Polaris and PlateSolve. Then goto that star from Stellarium (star should be centered if the mount got the new position from the PlateSolve). 

 

SharpCap should report the PlateSolve to the mount and the goto into Stellarium should show that.

 

The SW HC does not have a one star alignment in the the HC, so I am think if you do the above you will get the proper coordinates to the mount, but it's just a guess. 



#4 roelb

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Posted 14 July 2021 - 11:22 AM

When in ALT/AZ I'm afraid you have to carry out an initial alignment (by hand or auto StarSense).

Although this alignment doesn't require to be very accurate.

After doing that, one can use ASTAP from within SharpCap to plate solve and improve the alignment.



#5 RazvanUnderStars

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Posted 14 July 2021 - 12:18 PM

I used to have a Celestron Evolution mount (alt-az) and found that SharpCap worked very well during the initial alignment as well, which was a surprise, I had thought an alignment was required. Sometimes two solve-and-center clicks were required to accurately put the star in the crosshairs as the first one was close but not exact. I would expect this would work for the AZEQ5 as well, as there's no fundamental difference that I can think of.

 

If the mount's slew misses the alignment star by too much that plate solving doesn't work, there are two options:

  • simply slew the mount closer to the correct position - eyeballing is enough. You can do it from within SharpCap, you don't need the hand control. Then click on the solve-and-center button.
  • use a plate solver that can do blind solving as well (ASTAP is one and, I'd argue, the recommended solver anyway now).

The first option is painless, though and by preserving the non-blind solving in ASTAP, everything will be faster.

 

I'd suggest that the OP try it.



#6 roelb

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Posted 14 July 2021 - 01:29 PM

When turning the mount on.
Doing no alignment at all.
Connecting to SharpCap.
Will SC known where the mount is pointing to?
Using CPWI requires alignment first.
Using Stellarium or other planetary software will require the mount is properly sending its coordinates.
I wonder this will work.
Can you please describe each step you are make to achieve an alignment?

#7 RazvanUnderStars

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Posted 14 July 2021 - 02:07 PM

I used CPWI + SharpCap as follows (from what I remember, it's been 2-3 years since but used this procedure for more than a year until I changed mounts).

  • I started with the OTA horizontal, pointing towards north (this is because without an alignment, the mount's azimuth defaults to 0 so when it moves, it moves in the rough area where the stars are). I had the camera parallel to the ground as well.
  • Setup:
    • SharpCap is connected to the "CPWI mount" exposed by CPWI as an ASCOM device.
    • The plate solver in SharpCap has the correct FOV set up.
  • You start the alignment with CPWI and choose a star. The scope will slew, very roughly in that area. Nonetheless, CPWI will tell the mount "go to these RA/Dec coordinates" (not alt-az, the translation is done in the mount's firmware). Once it slewed there, I clicked on the solve-and-center button in SharpCap. SharpCap reads the coordinates from the mount (so it knows where it should be pointing), solves the image, tells the mount where it's actually pointing and then re-issues the goto to the coordinates of the alignment star.  Sometimes the centering is done in one step, at others you need one more attempt to refine the centering but the first one is close. Fundamentally, that's how StarSense must be working as well.
  • Choose a second alignment star and repeat the above.
  • Same if you want to add extra model points later.

I sold my StarSense when I realized the above worked every time (so just to avoid any misunderstanding, the above did not use StarSense). Try the above and let me know if something doesn't work, I'll try to remember or dig any message that I may have posted about this at the time.

 

Razvan


Edited by RazvanUnderStars, 14 July 2021 - 02:14 PM.

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#8 roelb

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Posted 14 July 2021 - 02:25 PM

Thanks Rasvan.
That was a clear explanation.
I'll try that next time out when weather permits.
I'll change the StarSense HC with the Nexstar+ first.
Will report my findings here.

#9 ex-Bubblehead

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Posted 14 July 2021 - 11:05 PM

I used CPWI + SharpCap as follows (from what I remember, it's been 2-3 years since but used this procedure for more than a year until I changed mounts).

  • I started with the OTA horizontal, pointing towards north (this is because without an alignment, the mount's azimuth defaults to 0 so when it moves, it moves in the rough area where the stars are). I had the camera parallel to the ground as well.
  • Setup:
    • SharpCap is connected to the "CPWI mount" exposed by CPWI as an ASCOM device.
    • The plate solver in SharpCap has the correct FOV set up.
  • You start the alignment with CPWI and choose a star. The scope will slew, very roughly in that area. Nonetheless, CPWI will tell the mount "go to these RA/Dec coordinates" (not alt-az, the translation is done in the mount's firmware). Once it slewed there, I clicked on the solve-and-center button in SharpCap. SharpCap reads the coordinates from the mount (so it knows where it should be pointing), solves the image, tells the mount where it's actually pointing and then re-issues the goto to the coordinates of the alignment star.  Sometimes the centering is done in one step, at others you need one more attempt to refine the centering but the first one is close. Fundamentally, that's how StarSense must be working as well.
  • Choose a second alignment star and repeat the above.
  • Same if you want to add extra model points later.

I sold my StarSense when I realized the above worked every time (so just to avoid any misunderstanding, the above did not use StarSense). Try the above and let me know if something doesn't work, I'll try to remember or dig any message that I may have posted about this at the time.

 

Razvan

Interesting solution.  When I can get a clear night I will try it.  The weather for the past few weeks has been either partly cloudy or mostly cloudy with a chance of T-storms...and it looks like that is continuing through the 10-day forecast...but targets of opportunity occasionally pop up!

 

Since it is a Sky Watcher mount I am not sure that the CPWI app will work, but I wonder if the SynScan Pro app would be able to achieve something similar.  I am mainly trying to avoid doing a traditional (2 star) alignment as I have a rats nest of wires going between the camera and the power supply (PPBA) sitting on the battery on the ground so every big slew is a bit sketchy at this point (getting that fixed is my next big project...).  It sounds like this method is a hybrid one so not quite what I was hoping for, but probably the best solution for this particular mount.



#10 ex-Bubblehead

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Posted 14 July 2021 - 11:07 PM

I used to have a Celestron Evolution mount (alt-az) and found that SharpCap worked very well during the initial alignment as well, which was a surprise, I had thought an alignment was required. Sometimes two solve-and-center clicks were required to accurately put the star in the crosshairs as the first one was close but not exact. I would expect this would work for the AZEQ5 as well, as there's no fundamental difference that I can think of.

 

If the mount's slew misses the alignment star by too much that plate solving doesn't work, there are two options:

  • simply slew the mount closer to the correct position - eyeballing is enough. You can do it from within SharpCap, you don't need the hand control. Then click on the solve-and-center button.
  • use a plate solver that can do blind solving as well (ASTAP is one and, I'd argue, the recommended solver anyway now).

The first option is painless, though and by preserving the non-blind solving in ASTAP, everything will be faster.

 

I'd suggest that the OP try it.

As noted above, I will give it a shot.  Thanks!



#11 ex-Bubblehead

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Posted 14 July 2021 - 11:12 PM

 You could try this (I use the StarSense control and have a different way of setting up (camera is on other scope)):

 

1. Plug into the USB connection, Setup your mount/scope to north and level. Manually (either with scope control in Stellarium or SharpCap ) move to Polaris and PlateSolve. Then goto that star from Stellarium (star should be centered if the mount got the new position from the PlateSolve). 

 

SharpCap should report the PlateSolve to the mount and the goto into Stellarium should show that.

 

The SW HC does not have a one star alignment in the the HC, so I am think if you do the above you will get the proper coordinates to the mount, but it's just a guess. 

I'll need to take a note of the initial reported mount position on a (non-parked) startup.  This is would be closer to what my desired solution would be.  I did not have the scope in the horizontal position initially, I roughed it to Polaris before powering on the mount...that may have been my downfall.

 

If only we had consistently clear nights right now...



#12 ex-Bubblehead

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Posted 14 July 2021 - 11:14 PM

I use SharpCap 3.2 with ASTAP on my german equatiorial mount (Mach 1) for initial and all subsequent alignments and so it can be done. However, I believe SharpCap is configured to assume a maximum alignment error in any GOTO of 15 degrees when platesolving, and so your initial goto must be within that accuracy for a successful initial sync-and-centre via ASTAP. If you use ASTAP as a standalone, you can configure the maximum alignment error for platesolving as well as other parameters. I don't know if SharpCap 4.0 allows more configuration of ASTAP parameters than vs3.2.

I did not try ASTAP in the standalone mode.  Sharpcap 4.0 still has the maximum error of 15 degrees (as far as I could tell).  I didn't think ASTAP had native support for commanding a mount via ASCOM.  I'll have to look into that further.



#13 dcweaver

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Posted 14 July 2021 - 11:46 PM

If you are running the Synscan Pro app, you don't have to do anything other than set the scope to level and North before powering on.  This sets a default pointing model.  Page 10-13 of the app manual discusses how to do this.

   

http://skywatcher.co...nd-synscan-app/

   

Basically, you are telling the mount where it is, when it is, and what it is pointing at before you move it.  That's enough to give it a rough sky model.  It isn't very accurate, but the goal is to be just accurate enough for SharpCap's plate solving interface to get you the rest of the way there.  SharpCap will fail if you are more than 15 deg off target, so you need to be rigorous about initial level and North (home position).  Once you have finished with the location and time info, you can do a goto.  That should get you close to the target.  Do a plate solve from SharpCap, and that should put you on target.  Be aware that the success of plate solving is tied to the field of view your telescope provides, and how much of the field is captured by the sensor.  Long focal lengths and small sensors are challenging.

   

Also, both goto and tracking will be rough.  To improve tracking you will need to add alignment points using the align with sync function.  You will have better accuracy in both if you set up in EQ mode and polar align.  SharpCap makes polar alignment easy.  Other than balancing the payload, it wouldn't be any harder than fussing with level and North for alt-az operation.  This type of workflow is common for people using EQ mounts, and is similar to what Errol (A3+) described.

 

+1 for Razvan also.  This is basically what he described using CPWI for Celestron products.


Edited by dcweaver, 14 July 2021 - 11:54 PM.


#14 alphatripleplus

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Posted 15 July 2021 - 06:49 AM

I did not try ASTAP in the standalone mode.  Sharpcap 4.0 still has the maximum error of 15 degrees (as far as I could tell).  I didn't think ASTAP had native support for commanding a mount via ASCOM.  I'll have to look into that further.

At the scope when aligning, I usually use ASTAP called by either SharpCap or CCDCiel and not in standalone mode. The only time I use it in standalone mode on the scope is to change ASTAP parameters that SharpCap does give direct access to. 



#15 Clouzot

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Posted 15 July 2021 - 09:34 AM

I used CPWI + SharpCap as follows (from what I remember, it's been 2-3 years since but used this procedure for more than a year until I changed mounts).

  • I started with the OTA horizontal, pointing towards north (this is because without an alignment, the mount's azimuth defaults to 0 so when it moves, it moves in the rough area where the stars are). I had the camera parallel to the ground as well.
  • Setup:
    • SharpCap is connected to the "CPWI mount" exposed by CPWI as an ASCOM device.
    • The plate solver in SharpCap has the correct FOV set up.
  • You start the alignment with CPWI and choose a star. The scope will slew, very roughly in that area. Nonetheless, CPWI will tell the mount "go to these RA/Dec coordinates" (not alt-az, the translation is done in the mount's firmware). Once it slewed there, I clicked on the solve-and-center button in SharpCap. SharpCap reads the coordinates from the mount (so it knows where it should be pointing), solves the image, tells the mount where it's actually pointing and then re-issues the goto to the coordinates of the alignment star.  Sometimes the centering is done in one step, at others you need one more attempt to refine the centering but the first one is close. Fundamentally, that's how StarSense must be working as well.
  • Choose a second alignment star and repeat the above.
  • Same if you want to add extra model points later.

I sold my StarSense when I realized the above worked every time (so just to avoid any misunderstanding, the above did not use StarSense). Try the above and let me know if something doesn't work, I'll try to remember or dig any message that I may have posted about this at the time.

 

Razvan

I second that procedure, that's exactly how I align my alt-az Evolution mount. The fact that you start with the OTA level and pointing north is enough for the first slew to be reasonably close to the first alignment point: the mount already knows where it is, more or less, even before you start aligning.

For the Skywatcher users, SynScan also allows that kind of alignment procedure ("North Level Alignment") but with two stars only, as opposed to CPWI which can build a much more complex model with multiple stars.


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#16 ex-Bubblehead

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Posted 15 July 2021 - 11:55 PM

Just a progress update for posterity:

 

Assuming the mount was not parked at power down, EQMod will assume it is pointing at the celestial north (DEC = 90, RA = various, Alt = Lat, Az = 0 for the northern hemisphere).  There are no settings to change this default behavior.  Essentially pointing at polaris.  I figure there are two easy options at this point.

 

1. Align the altitude setting circle and when setting up the mount, eyeball the azimuth and set the altitude to the latitude using that.  That should be close enough to plate solve and synch the encoders from SC without it blowing up on me.

 

2.  Set a defined park position of horizontal and pointing north.  When setting up the mount, eyeball both.  At that point, just slew up and find some stars to plate solve and synch with...again, it should be close enough.  To be even more froggy, an unpark position can be defined to have the scope slew up to ~Polaris automatically.  This option more closely resembles how the synscan app works.

 

I'll probably set the setting circles AND define the park/unpark positions just to give myself options.

 

To dcweaver's point about going to an EQ setup, I'm notionally keeping the second mounting option available to toss on my AWB for comparisons/visual practice/to look impressive for the neighbers/etc...


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#17 roelb

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Posted 20 July 2021 - 06:38 PM

I used CPWI + SharpCap as follows (from what I remember, it's been 2-3 years since but used this procedure for more than a year until I changed mounts).

  • I started with the OTA horizontal, pointing towards north (this is because without an alignment, the mount's azimuth defaults to 0 so when it moves, it moves in the rough area where the stars are). I had the camera parallel to the ground as well.
  • Setup:
    • SharpCap is connected to the "CPWI mount" exposed by CPWI as an ASCOM device.
    • The plate solver in SharpCap has the correct FOV set up.
  • You start the alignment with CPWI and choose a star. The scope will slew, very roughly in that area. Nonetheless, CPWI will tell the mount "go to these RA/Dec coordinates" (not alt-az, the translation is done in the mount's firmware). Once it slewed there, I clicked on the solve-and-center button in SharpCap. SharpCap reads the coordinates from the mount (so it knows where it should be pointing), solves the image, tells the mount where it's actually pointing and then re-issues the goto to the coordinates of the alignment star.  Sometimes the centering is done in one step, at others you need one more attempt to refine the centering but the first one is close. Fundamentally, that's how StarSense must be working as well.
  • Choose a second alignment star and repeat the above.
  • Same if you want to add extra model points later.

I sold my StarSense when I realized the above worked every time (so just to avoid any misunderstanding, the above did not use StarSense). Try the above and let me know if something doesn't work, I'll try to remember or dig any message that I may have posted about this at the time.

 

Razvan

I tried the above procedure with the Evolution 8 ALT/AZ using CPWI, SharpCap, ASTAP with the ZWO ASI533MC-Pro.

But couldn't achieve a satisfying overall alignment.

For every point in the sky I was forced to plate solve at least twice.

After some alignment points plate solving was even not possible.

One must set higher gain/exposure to succeed plate solving, which is rather time consumingfrown.gif

Will try when I have some EAA spare time.

Using StarSense is a lot faster.



#18 RazvanUnderStars

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Posted 20 July 2021 - 09:39 PM

Interesting to hear - I'm intrigued that it didn't work so, purely for scientific reasons (as you have an alternative solution), below are some thoughts on why plate solving may have failed. As a curiosity, do you happen to still have the images that were not solved?

  • correct star detection (the first step in a plate solving attempt) is influenced by the exposure times. A low gain or bright sky (if the alignment was made during dusk) may prevent the stars from being properly detected or distinguished from hot pixels. At the time I was using a high gain (~400) and exposures under 10s, set right from the start.
  • if blind platesolving was used, maybe the issue was the smaller FOV of the 533 - at the time I was using a 294MC Pro. Blind plate solving & smaller FOV could be a difficult combination, but here ASTAP's author would be more qualified to comment (there have been discussions about this here on CN, but don't remember the limits)
  • another possible cause is very long exposure times (if a low gain was used) which, in the absence of a tracking model, yet to be built, could cause the stars to be lines instead of points - this is known to cause plate solving failures, much like imperfect focus.

 

I ran into the first and third issues myself at various times.

 

Hope this helps,

Razvan



#19 ex-Bubblehead

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Posted 20 July 2021 - 11:19 PM

I think I got everything sorted out.  So to pull a Paul Harvey:

 

My previous plan as noted did not work as intended.  After a couple hours of struggling to square the circle, I did some additional research and realized that EQMOD will struggle to drive an ALTAZ scope because it assumes the declination/altitude axis is inclined to match the latitude.  Playing around with the EQMOD simulator in Stellarium and watching the scope motion for different slew commands pretty much put the nail in that coffin for me.

 

I had previously assumed that the synscan pro app was not able to be interfaced with other programs (Stellarium/SC), but some more digging showed that to be false.  While researching the topic, I found the steps used by someone to associate the app with ASCOM.  A little more experimentation showed that Stellarium and SC could both talk with synscan pro simultaneously.  When I put it in to practice on Monday night, I thought everything had been solved, then I noticed some serious star trails happening starting at about 15 seconds exposure time. 

 

After a couple hours of troubleshooting, I felt that one reasonable explanation was that I had the OTA mounted upside down with respect to the altitude axis (so that raising the scope in altitude actually made the axis reading become more negative) which was an issue I had to work through when I first got the mount and goto and tracking did not work right.  The tip off there was that the HC directional arrows made the scope operate opposite from what was expected.  So the scope operated more like an airplane...pull back to tilt the nose up.  After cycling scope power to plug in the HC and remove the USB connection, I performed a normal 2-star alignment...and the problem disappeared.  Doing a quick reflection, I realized that I must have mis-targeted a star during the synscan pro alignment.  Racing against time to get the alignment done before I lost 1 of the handful of available stars behind a tree, I ended up a few seconds late and was left with basically a barely visible polaris being the only star I was sure of.  The night had been very hazy with almost no visible stars, and using SkySafari on the phone to try to identify the ones that were visible, I must have gotten them mixed up and aligned on the wrong star.  That seemed the most likely explanation for my tracking issue.

 

The following night (tonight) was slightly clearer (I didn't have to avert my eyes to see Polaris, barely), but I confirmed I had a good shot at Vega, Deneb, Polaris, and Arcturus for alignment.  I did a North horizontal two-star alignment on Arcturus and Polaris, did a couple slews and syncs to refine the alignment...and the rest of tonight went pretty much as ideally as it could have, given the poor seeing conditions.

 

So at this point I have a solution that works well enough for now, and it is just a matter of making it more efficient, I think.

 

And now you know...the rest! of the story.


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#20 roelb

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Posted 21 July 2021 - 06:02 PM

Interesting to hear - I'm intrigued that it didn't work so, purely for scientific reasons (as you have an alternative solution), below are some thoughts on why plate solving may have failed. As a curiosity, do you happen to still have the images that were not solved?

  • correct star detection (the first step in a plate solving attempt) is influenced by the exposure times. A low gain or bright sky (if the alignment was made during dusk) may prevent the stars from being properly detected or distinguished from hot pixels. At the time I was using a high gain (~400) and exposures under 10s, set right from the start.
  • if blind platesolving was used, maybe the issue was the smaller FOV of the 533 - at the time I was using a 294MC Pro. Blind plate solving & smaller FOV could be a difficult combination, but here ASTAP's author would be more qualified to comment (there have been discussions about this here on CN, but don't remember the limits)
  • another possible cause is very long exposure times (if a low gain was used) which, in the absence of a tracking model, yet to be built, could cause the stars to be lines instead of points - this is known to cause plate solving failures, much like imperfect focus.

 

I ran into the first and third issues myself at various times.

 

Hope this helps,

Razvan

Agree with all your statements.




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