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alignment of an AZ mount with Sharpcap

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#1 zoltrix

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Posted 30 November 2021 - 06:45 PM

Hello

I own an AZ GTi mount (no wedge)
In my Bortle 9 sky even the alignment of the mount can be a pain
Yet a reasonable number of stars is visible on the screen of my PC
I wonder whether Sharpcap plate solving function could be of help

I mean

1) I use the "North and level " method of synscan pro
2) the mount slews to the first star but it slightly miss it
3) I center the star with plate solving

Unfortunately it seems to me that Sharpcap does not know which stars I have selected from the synscan menu
Is there a way to overcome that issue ?

#2 Rac19

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Posted 30 November 2021 - 06:58 PM

I have found Sharpcap plate solving to correct and synch my alignment model very accurately. It requires that you have a reasonable alignment though and won't correct if the error is more than 15 degrees. It can't "blind solve", in other words, and needs to have a rough idea of where the OTA is pointed. 

 

Can you see the current coordinates in  Sharpcap telescope panel? It won't work if you can't see them. Sharpcap reads these coordinates (not the name of the target star) , compares them to the the plate solves results, calculates the error and corrects it, if the error is less than 15 degrees.



#3 zoltrix

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Posted 30 November 2021 - 07:43 PM

hi Richard

you got my point
Actually the current coordinates in Sharpcap telescope panel do not match the ones of my first selected star
Sharpcap can not get data from synscan
However I wonder whether Sharpcap can accept them as a manual input from user
with "north level " method the scope automatically slews to my first star and it miss the target but the error is definitely less than 15 degrees

Alberto

Edited by zoltrix, 30 November 2021 - 07:43 PM.


#4 barbarosa

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Posted 30 November 2021 - 07:59 PM

It would be worthwhile to read the SC help file sections on setting up plate solving and the options for how it is used. SharpCap does not plate solve, it calls the plate solving application that the user selects and installs. The user than selects some options such as solve and sync to determine what happens when you invoke plate solving from the SC menu. You can set it up for blind solving but most folks use a faster option to look at within some set limit around the current coordinates.

 

SharpCap essentially get the pointing information from the mount via ASCOM and passes it to the solver.

 

I have a permanent EQ setup and no longer bother to align. I just do a plate solve and sync.

 

My guess is that  with an Alt -az mount you cannot do a solve and sync unless the mount is aligned. You might try doing this--

 

For whatever plate solving app you use, download a larger data set, on that can deal with a large pointing error. Do a one star alignment Just assume that the slew is accurate and accept it. The mount now "thinks" it is pointed at some coordinates. Then invoke plate solving to solve and sync. This should correct the initial pointing error. Then go on from there using the hand control or software to point the mount, plate solving again if necessary. The second solve should be fast.



#5 ButterFly

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Posted 30 November 2021 - 08:05 PM

You need an alignment first, so that the scope can know where it is and send out coordinates.  Alt/Az mounts must be star aligned and know when and where they are in order to track properly.  A mere sync may not cut it for the long term, especially near zenith.

 

What you are suggesting can be done with Celestron mounts using CPWI.  I can platesolve, then inject the coordinates into the CPWI model.  I cannot do this with a handcontroller model, so I need to use a computer.  I have an EQ mount, so the utility is precisely zero.  The tracking for EQ mounts, or a wedge, is controlled by the polar alignment, not the star alignment.  I just "Quick Align" after a polar alignment, platesolve to where I need to go, then it tracks based on the polar alignment.

 

Skywatcher and Celestron are owned by the same company, so there may be something coming down the road.  In the meantime, get a wedge.



#6 Rac19

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Posted 30 November 2021 - 11:36 PM

Not being an expert on this subject, but having some experience...

 

I am pretty sure that Sharpcap has to be connected to the mount and receiving coordinates from it. I don't think that there is a way to manually enter them into Sharpcap.

 

I would have thought that it would be possible to connect the SynScan, via its ASCOM driver. Once that is done you should see the correct coordinates, from the mount, displayed in Sharpcap and Sharpcap could be able to slew to that precise position very accurately, after plate solving.

 

By the way, is plate solve actually successful? If not some exposure adjustments may be required to show enough stars but not to many. The image must also be in focus of course, by the way. Another consideration is that the field of view must by wide enough to capture a pattern of stars that large enough to be solved.

 

You do need to have reasonably calibrated alignment model before you start, Sharpcap will adjust an established alignment model but won't create one from scratch.



#7 zoltrix

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Posted 01 December 2021 - 03:59 AM

Hi

No , the plate solve is not succesful but I dont think it is a matter of exposure adjustments
I tried and tried even with different sigma values.
The point is that the coords shown in the telescope panel are not the ones of my target thus the error may be higher than 15°
it seems that sharpcap can comunicate with the mount only after being aligned so it is of no help for the alignment of an AZ mount only for an EQ
I tend to believe that it is an oversight which can be easily fixed

I will try a David's suggestion,enanched version smile.gif

1) I do a one star alignment
2) I accept it
3) I plate solve
4) I exit the procedure
5) I repeat the one star alignment with the same star
6) a few seconds later the star should be still reasonably centered
7) I accept it

Edited by zoltrix, 01 December 2021 - 04:23 AM.


#8 Rac19

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Posted 01 December 2021 - 05:52 AM

it seems that sharpcap can comunicate with the mount only after being aligned so it is of no help for the alignment of an AZ mount only for an EQ

I know for sure that the Celestron mounts will communicate regardless of alignment status, and the coordinates will be displayed in Sharpcap, even if they are nominal initially nominal, say North or South and horizontal.

 

The fact remains that you do need to have an active alignment model and you need to within 15 degrees accuracy before Sharpcap plate solve can work. Actually, the 15 degree limit might apply mainly to re-centering.

 

One question that I have seen on another thread, are the mount and the software (Sharpcap) using the same epoch (J2000, JNOW etc)? I am not sure that a discrepancy would result in a 15 degree error though.

 

Also, is you field of view wide or narrow (low f ratio or high f ratio)? If it is too narrow plate solving won't work.

 

Does Sharpcap provide a reason for plate solve failing?


Edited by Rac19, 01 December 2021 - 03:40 PM.


#9 alphatripleplus

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Posted 01 December 2021 - 08:18 AM

Hello

I own an AZ GTi mount (no wedge)
In my Bortle 9 sky even the alignment of the mount can be a pain
Yet a reasonable number of stars is visible on the screen of my PC
I wonder whether Sharpcap plate solving function could be of help

 

Which plate solving software are you using with SharpCap?



#10 zoltrix

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Posted 01 December 2021 - 08:26 AM

hello

I have a newtonian 130/650 , the FOV should not be too narrow
I get an error message but it does not make any sense
"maybe too many stars ?"
The point is that I am in Bortle 9
However I can play with the parameters but nothing changes
I am reasonably sure that plate solve fail because Sharpcap considers a target which is far away from my target
anyway you confirm that it should not be that difficult to comunicate the coords of the target regardless of the alignment status

#11 zoltrix

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Posted 01 December 2021 - 08:27 AM

Which plate solving software are you using with SharpCap?


all sky plate solver

#12 RazvanUnderStars

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Posted 01 December 2021 - 08:52 AM

A couple of years ago I had a Celestron Evolution mount and an 8" SCT and was using CPWI for alignment and SharpCap+ASTAP for platesolving, including assisting in centering the alignment stars. In other words, doing a plate solve & sync was replacing the manual centering of the alignment star. So only one alignment attempt was needed. The mount was just pointing roughly in the area of the sky of the target star; if it went too far I slewed it closer by eyeballing it, which was fairly easy since the alignment stars are typically bright.

 

So the entire alignment process was starting with the OTA horizontal and pointing to the north, then clicking an alignment star in CPWI, then clicking solve & sync in SharpCap, then repeat for other stars.

 

OP, I'd suggest the above process and also to replace the older ASPS with ASTAP which is faster & better and can also do blind solves, although you shouldn't need that.



#13 zoltrix

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Posted 01 December 2021 - 09:20 AM

thanks

It is what I supposed possible with Sharpcap i.e :

"Assisting in centering the alignment stars "

I will try with ASTAP but I doubt it can work
a CPWI like function is needed
it should not be that hard to implement it ( I hope)

#14 RazvanUnderStars

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Posted 01 December 2021 - 09:33 AM

I'm in Bortle 9 as well and it worked very well with ASTAP - make sure the exposure is set appropriately so stars can be recognized, this is a common reason for failure, especially if aligning during late dusk, when the sky is still bright. In Sharpcap, adjust the black level and check the number of stars shown. 



#15 zoltrix

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Posted 01 December 2021 - 12:52 PM

hi

do you mean that you can plate solve even though your AZ mount is not aligned ?
in other words Sharpcap can be of help for alignment thanks to the plate solving function ?
If so I immediately download ASTAP :
I am concerned about Bortle 9 just in case of "electronically non assisted alignment "
sometimes in the zone of sky which I can see from my balcony not even a star is visible
Yet in the snapshot at least 15 stars or even more are alwayes present

Edited by zoltrix, 01 December 2021 - 12:56 PM.


#16 ButterFly

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Posted 01 December 2021 - 01:22 PM

Plate solving is separate from syncing the mount.

 

I can plate solve an image I got from the internet, or if I draw well enough, one that I hand drew then scanned.  A plate solve only determines where in the sky that is.

 

Syncing the mount tells the mount "this is where you actually are".  When the mount's alignment thinks it is too far from where it actually is, syncing will fail.



#17 RazvanUnderStars

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Posted 01 December 2021 - 02:11 PM

Yes. I've done it for months (and immediately sold my StarSense once I realized). The process is done, whether the mount is aligned or not, because even during the alignment, the mount has a model - it's going to be off a lot, of course, but it's still there, that's why once you start from north, the first slew is still in the area of the target star. With each star, the model is refined. And again, make sure to be in the area of the star by slewing manually if the mount doesn't get close enough. ASTAP can do blind solving, but it's best to help it by simply being in the vicinity of the target instead (plus blind solving may require tweaks to the configuration, I don't remember, it's been a while since I use it).

 

 

do you mean that you can plate solve even though your AZ mount is not aligned ?
in other words Sharpcap can be of help for alignment thanks to the plate solving function ?
If so I immediately download ASTAP


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#18 steveincolo

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Posted 01 December 2021 - 04:01 PM

hi

do you mean that you can plate solve even though your AZ mount is not aligned ?
in other words Sharpcap can be of help for alignment thanks to the plate solving function ?
If so I immediately download ASTAP :
I am concerned about Bortle 9 just in case of "electronically non assisted alignment "
sometimes in the zone of sky which I can see from my balcony not even a star is visible
Yet in the snapshot at least 15 stars or even more are alwayes present

That is what I do, but with an iOptron AZ Mount Pro and an ASIAIR Pro.  Turn on the mount without aligning, do a plate solve, and sync the results to the mount.  Voila, mount is now aligned. 


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#19 zoltrix

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Posted 02 December 2021 - 02:38 AM

hello

so, it must be a synscan only related issue

#20 Rac19

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Posted 02 December 2021 - 06:24 AM

I was inspired by this topic to experiment a little when I got clear skies, for the first time in a couple of weeks.

 

I have been using "save alignment and park" in CPWI which is great when it works. Unfortunately CPWI seems to regularly loose the plot (and the alignment model)  in mid-session, as it did on my last outing.

 

On connecting to the scope tonight, I used a CWPI option to "use the last alignment", I was instructed point the scope North (being in the Southern Hemisphere) and parallel to the wedge plate. I ignored the instruction to GoTo a star and sync the model on it.

 

Instead, after doing a GoTo a prominent star, I did a plate solve and sync/centre in Sharpcap. After successfully solving, Sharpcap reported a 2 degree error, synchronised the alignment model and centred the star.  It wasn't even in view after the GoTo but was dead centre after plate solving. I assume that I could have have skipped the GoTo and pointed the 'scope anywhere that there were stars. It was reassuring to see a known target being centred though.

 

I should point out that I have a permanent mount with a wedge, so it's not difficult to be with 15 degrees in this circumstance.

 

EDIT: So plate solving allowed me to avoid another StarSense align. There was a small issue in fact because the 'scope was way out of focus due to changing from a 2.5x Powermate to a 0.5x reducer. Reasonable focus was obviously required before a plate solve could be attempted.


Edited by Rac19, 02 December 2021 - 07:02 AM.

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