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Starsense alignment and goto approach questions

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#1 Cfeastside

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Posted 16 July 2020 - 10:42 AM

Have some questions maybe y’all could shed some light on.
1.  Re adding alignment reference points:  If I need to calibrate starsense camera, should I add these after the first auto alignment, or after I calibrate and do the post starsense calibration auto alignment?  I guess I’m wondering if the ref points get wiped out when redoing the auto alignment after calibrating the starsense camera.

 

2.  Starsense handcontroller, Goto Approach:  my 9.25 evo is front heavy so trying to set altitude to NEGATIVE.  Tried this last night and hand controller still says to slew up and right when adding alignment reference points.  Won’t store the point unless I do that, wants that check mark.  Been having drift issues and gotos are putting star at edge of field even with backlash settings applied, so trying this negative setting to see if it helps.  Has this been your experience?  Is this right or a bug in the firmware?  Handcontroller is up to date firmware wise (1.20.20162).  Just redid it this morning, for 

 

9.25 evolution with starsense

all firmware up to date 

 

thanks!


Edited by Cfeastside, 16 July 2020 - 10:43 AM.

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#2 deansjc

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Posted 16 July 2020 - 02:10 PM

I wish I knew the answer to this one. Logically the HC should call for the final move based on this setting. I am interested in what replies come in. I have the BexStar users Giude and will see if Mike Swanson has provided guidance on this specific question. He has as related to alignment manually.

#3 Noah4x4

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Posted 16 July 2020 - 03:40 PM

1. Add additional alignment points after your primary alignment and calibration. 

 

In effect, you are adding SYNC points dotted around the sky. I added an initial ten. Then each month I would replace one that had dropped below the horizon with a new one in view. Over ten months, I developed a perfect all year round set whereby at any one time I had perhaps six currently available. My Starsense accuracy has always been awesome since then . But see next....

 

2.  My 8" Evolution is seriously front end loaded as I either use Hyperstar or must put my OTA at its optimum forward position to get sufficient rear end camera clearance at f/6.3.

 

I have not found balance or GoToApproach to have any significant impact on Starsense performance or Evo tracking, albeit it is sensible to eliminate this possibility. The powerful Evolution motors and metal gears nullify most mechanical aberations and there is no comparison with (say) an 8SE. But like you, my early GoTos were not perfect.

 

What I eventually discovered was how difficult it is to EXACTLY centre a star in an eyepiece during (say) alignment or calibration etc. This is crucial, particularly if trying to eliminate polar alignment error during an ASPA. I now defocus and progressively use ever greater EP magnification to ever more accurately centre the enlarged airy disk (which is easier to centre than a pin-point star).  I finish using a 12mm illuminated cross hair reticle EP.  

 

I leave my scope fully assembled and the diligence above delivered great performance for three years with Starsense HC. It came as shock to discover that I had to repeat all when I embraced CPWI. But once again, my GoTos are precise. I reckon taking more care with this step is probably more important than fiddling with backlash, Gotoapproach or other like settings. It's not easy to find the precise centre of an eyepiece, especially if you wear spectacles, unless you follow my suggested technique.


Edited by Noah4x4, 16 July 2020 - 03:43 PM.


#4 Cfeastside

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Posted 16 July 2020 - 08:16 PM

1. Add additional alignment points after your primary alignment and calibration. 

 

In effect, you are adding SYNC points dotted around the sky. I added an initial ten. Then each month I would replace one that had dropped below the horizon with a new one in view. Over ten months, I developed a perfect all year round set whereby at any one time I had perhaps six currently available. My Starsense accuracy has always been awesome since then . But see next....

 

2.  My 8" Evolution is seriously front end loaded as I either use Hyperstar or must put my OTA at its optimum forward position to get sufficient rear end camera clearance at f/6.3.

 

I have not found balance or GoToApproach to have any significant impact on Starsense performance or Evo tracking, albeit it is sensible to eliminate this possibility. The powerful Evolution motors and metal gears nullify most mechanical aberations and there is no comparison with (say) an 8SE. But like you, my early GoTos were not perfect.

 

What I eventually discovered was how difficult it is to EXACTLY centre a star in an eyepiece during (say) alignment or calibration etc. This is crucial, particularly if trying to eliminate polar alignment error during an ASPA. I now defocus and progressively use ever greater EP magnification to ever more accurately centre the enlarged airy disk (which is easier to centre than a pin-point star).  I finish using a 12mm illuminated cross hair reticle EP.  

 

I leave my scope fully assembled and the diligence above delivered great performance for three years with Starsense HC. It came as shock to discover that I had to repeat all when I embraced CPWI. But once again, my GoTos are precise. I reckon taking more care with this step is probably more important than fiddling with backlash, Gotoapproach or other like settings. It's not easy to find the precise centre of an eyepiece, especially if you wear spectacles, unless you follow my suggested technique.

Thanks noah for the detailed reply.  The frustrating thing is im using a 12mm illum ep when calibrating and setting the additional ref pts.  Unfortunately i have break my setup down each time.   



#5 Michael_Swanson

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Posted 16 July 2020 - 09:11 PM

Have some questions maybe y’all could shed some light on.
1.  Re adding alignment reference points:  If I need to calibrate starsense camera, should I add these after the first auto alignment, or after I calibrate and do the post starsense calibration auto alignment?  I guess I’m wondering if the ref points get wiped out when redoing the auto alignment after calibrating the starsense camera.

 

2.  Starsense handcontroller, Goto Approach:  my 9.25 evo is front heavy so trying to set altitude to NEGATIVE.  Tried this last night and hand controller still says to slew up and right when adding alignment reference points.  Won’t store the point unless I do that, wants that check mark.  Been having drift issues and gotos are putting star at edge of field even with backlash settings applied, so trying this negative setting to see if it helps.  Has this been your experience?  Is this right or a bug in the firmware?  Handcontroller is up to date firmware wise (1.20.20162).  Just redid it this morning, for 

 

9.25 evolution with starsense

all firmware up to date 

 

thanks!

Hi,

 

With StarSense (and the SkyPortal/SkySafari apps using Celestron WiFi) additional alignment points improve the system's model of the sky, correcting for physical mount imperfections.  An alignment with 2 points must assume the azimuth, altitude and optical axes are perfectly orthogonal (perpendicular in 3 dimensions).  In practice, I find that a total or 5 or 6 alignment points is the sweet spot.  For most methods of use of the scope (i.e. taking it back in the house/garage between uses), you will always need to do a new alignment each session and must add 5/6 points each time you align (for best accuracy).  So, as I suggest in my book, you should perform the initial alignment and then add another 2 or 3 alignment points before you perform the camera calibration (generally a one-time requirement).  I also explain how you can store the current alignment routine to automate it later as a User Auto Align - creating your own alignment routine that automatically adds 5/6 alignment points (I've posted some of those details here on Cloudy Nights as well but haven't kept links to the specific discussion threads).

 

Regarding GoTo Approach - sorry, as noted in my book, changes to that are busted in StarSense.  I do recommend front-heavy scopes have the GoTo Approach for ALT set to NEG but unfortunately StarSense still uses POS even when you make the change.  Fortunately, there is relatively little gear backlash in the Evolution mount so the effects of this are relatively minor and you will just need to live with it (unless Celestron ever addresses this - but I informed them of the issue over 3 years ago...).

 

Since the GoTo Approach is POS, when adding additional alignment points, use the RIGHT and UP arrows as the final motion to the alignment point (there is no reversal of UP/DOWN arrows in that procedure).

 

Best regards,
Mike Swanson
https://www.NexStarSite.com

 

 


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#6 beammeup

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Posted 17 July 2020 - 07:35 AM

Have some questions maybe y’all could shed some light on.
1.  Re adding alignment reference points:  If I need to calibrate starsense camera, should I add these after the first auto alignment, or after I calibrate and do the post starsense calibration auto alignment?  I guess I’m wondering if the ref points get wiped out when redoing the auto alignment after calibrating the starsense camera.

 

2.  Starsense handcontroller, Goto Approach:  my 9.25 evo is front heavy so trying to set altitude to NEGATIVE.  Tried this last night and hand controller still says to slew up and right when adding alignment reference points.  Won’t store the point unless I do that, wants that check mark.  Been having drift issues and gotos are putting star at edge of field even with backlash settings applied, so trying this negative setting to see if it helps.  Has this been your experience?  Is this right or a bug in the firmware?  Handcontroller is up to date firmware wise (1.20.20162).  Just redid it this morning, for 

 

9.25 evolution with starsense

all firmware up to date 

 

thanks!

I use my AVX mount with CPWI and Starsense.

I also find that I get drift if the polar alignment is not precise.

Of course the AVX tracks in RA only I believe.

For EQ mounts, in CPWI you can also activate tracking in both axes by selecting the “Ra + Dec Tracking” checkbox. This can be useful to use if your polar alignment isn’t very good.


Edited by beammeup, 17 July 2020 - 07:36 AM.


#7 Cfeastside

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Posted 20 July 2020 - 08:19 AM

 

Hi,

 

With StarSense (and the SkyPortal/SkySafari apps using Celestron WiFi) additional alignment points improve the system's model of the sky, correcting for physical mount imperfections.  An alignment with 2 points must assume the azimuth, altitude and optical axes are perfectly orthogonal (perpendicular in 3 dimensions).  In practice, I find that a total or 5 or 6 alignment points is the sweet spot.  For most methods of use of the scope (i.e. taking it back in the house/garage between uses), you will always need to do a new alignment each session and must add 5/6 points each time you align (for best accuracy).  So, as I suggest in my book, you should perform the initial alignment and then add another 2 or 3 alignment points before you perform the camera calibration (generally a one-time requirement).  I also explain how you can store the current alignment routine to automate it later as a User Auto Align - creating your own alignment routine that automatically adds 5/6 alignment points (I've posted some of those details here on Cloudy Nights as well but haven't kept links to the specific discussion threads).

 

Regarding GoTo Approach - sorry, as noted in my book, changes to that are busted in StarSense.  I do recommend front-heavy scopes have the GoTo Approach for ALT set to NEG but unfortunately StarSense still uses POS even when you make the change.  Fortunately, there is relatively little gear backlash in the Evolution mount so the effects of this are relatively minor and you will just need to live with it (unless Celestron ever addresses this - but I informed them of the issue over 3 years ago...).

 

Since the GoTo Approach is POS, when adding additional alignment points, use the RIGHT and UP arrows as the final motion to the alignment point (there is no reversal of UP/DOWN arrows in that procedure).

 

Best regards,
Mike Swanson
https://www.NexStarSite.com

 

 

 

Thanks michael!  I do have your book at it has been very helpful

 

i was able to get very precise gotos with stars showing up in my 12mm ep after modifying my methods.  This without the scope on the wedge.   Unfortunately when i use the wedge gotos just suck.  Pretty consistantly putting stars at the edge of a 22mm ep or just outside of fov of the 22 ep.  further issue is if i try to refine my polar alignment error each additional result seems to make it worse.  After the third polar alignment attempt upon initiating a new auto alignment starsense points below the horizon and locks up. This seems to be a pattern as this is the third time its done this.  

 

Looking through past posts regarding starsense and wedge usage many seem to have similar issues with poor gotos when on the wedge vs without.  Really scratching my head on this. A recent user posted similar issues and after talking with celestron he modified his goto approach and they seemed to improve his gotos.  Though he had a back heavy scope and changed alt setting to pos instead of neg.  i was hoping by changing my alt to neg would improve things but it hasnt.  

 

I am using a compass to orient to true north and my initial PE isnt too bad but am trying to get in seconds off in both directions instead of minutes.   Iam using the starsense hc to do my alignments.  Usinf skysafari has similar results.  The hc reports an alignment error of 4-5 minutes in each direction when on the wedge.   Ill have to check that when not using the wedge.

 

At this point i will try the following, 1) manual alignment using starsense and will shut scope off after doing Polar alignment, 2) not use starsense and try the nexstar plus hc.   

 

All firmware is upto date.  If anyone has any suggestions on improving goto accuracy on a wedge id appreciate it.   



#8 Michael_Swanson

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Posted 20 July 2020 - 08:16 PM

I don't have a lot of experience with StarSense on a wedge.  Updated firmware is definitely important and you have already taken care of that.  You must also change the HC menu setting to let the system know you are on a wedge (see page 116 in the book).  Since you cannot change GoTo Approach in StarSense (well, again, you can change it but it ignores the change), just be sure all finally movements to add additional alignment points finish with the RIGHT and UP arrows, even on a wedge.  Balance of a fork-mount on a wedge is pretty tricky - seek out the balance article on Starizona.com for good tips.

 

When operating on a wedge, are you still adding multiple alignment points?  One tip that might help is to only add alignment points below the celestial equator.  You would use the StarSense Manual align to do this.  Then only point at objects towards the south.  The reason I think this might help is that it avoids the changing balance that occurs when you point higher in the sky or towards the north.  This will in turn avoid any backlash induced inaccuracies.

 

Best regards,
Mike Swanson
https://www.NexStarSite.com



#9 Cfeastside

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Posted 23 July 2020 - 09:04 AM

I don't have a lot of experience with StarSense on a wedge.  Updated firmware is definitely important and you have already taken care of that.  You must also change the HC menu setting to let the system know you are on a wedge (see page 116 in the book). yes, thats being done Since you cannot change GoTo Approach in StarSense (well, again, you can change it but it ignores the change), just be sure all finally movements to add additional alignment points finish with the RIGHT and UP arrows, even on a wedge.  Balance of a fork-mount on a wedge is pretty tricky - seek out the balance article on Starizona.com for good tips.

 

When operating on a wedge, are you still adding multiple alignment points?yes  One tip that might help is to only add alignment points below the celestial equator.  You would use the StarSense Manual align to do this.  Then only point at objects towards the south.  The reason I think this might help is that it avoids the changing balance that occurs when you point higher in the sky or towards the north.  This will in turn avoid any backlash induced inaccuracies.  thats a Good idea.  I’m thinking this is a balance issue when on the wedge.  Thanks for tips and suggestions!

 

Best regards,
Mike Swanson
https://www.NexStarSite.com



#10 Ddaniel84

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Posted 25 July 2020 - 02:51 AM

Hi Mike
I've a question for you. My setup is C8Ev + wedge + Starsense. What is the best accuracy I can obtain with such setup? After ASPA it says that RMS is 0 but Polar Error South (or north) some minutes and the same for polar error East (or West).
How it's possible?
Last when using then PHD2 the polar error alignment can be evaluated between 5 to 15' !!!
Dom

#11 Michael_Swanson

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Posted 26 July 2020 - 09:21 PM

Hi Dom,

 

There are two different accuracy issues to consider when polar aligned.  One is GoTo accuracy, the other is tracking accuracy.  GoTo accuracy is depending upon a large number of factors but you should be able to get very good accuracy with StarSense, particularly if you add at least 5 or 6 total alignment points. 

 

Tracking accuracy is dependent upon how close you are to "prefect" with your polar alignment, the accuracy of the motor moving at the correct rate (usually very, very good on Celestron's mounts), and the perfection of the gears (good, but certainly not perfect on an Evolution) and how you have the system balanced.  Other factors can sometimes come into play, such as binding of the worm gear, excess movement of a drive or mount component, binding of an axis, etc.

 

ASPA is good, but not perfect.  It gets you a quite accurate polar alignment rather quickly.  Polar alignment can be improved upon using a drift alignment (Google is your friend).  That said, for any exposures shorter than 10 minutes (and it is rare to use longer exposures these days), ASPA is probably all you need and you should perfect your autoguiding for the last bit of tracking accuracy required for good results.

 

And that's about as far as I can take you down that road as I'm not an avid astrophotographer.

 

Best regards,
Mike Swanson
https://www.NexStarSite.com



#12 Ddaniel84

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Posted 26 July 2020 - 11:41 PM

Thanks a lot Mike. It's very precious.
I've no problem in finding objects. Accuracy should be less than 1' for a FOV of 25'.
Problem is tracking. I've improved polar alignment with PHD2 drifting polar alignment and will now consider it is the reference. But it's not stable. I'm building a fix and permanent basement to receive the wedge and will pay a large attention in mounting the wedge.
I cross fingers and hope all of that will reduce instability. Sharpcap seems to have a better procedure for polar alignment. But polaris has to be seen. I try to elevate my setup for that. I will also pay more attention in balancing the system. But how to appreciate quality of gear?
Dom

#13 Michael_Swanson

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Posted 26 July 2020 - 11:45 PM

Hi Dom,

 

Lower quality gears result in short and sometimes dramatic errors in tracking (but so do imbalance, friction issues, other mechanical issues).  Autoguiding can usually deal with any moderate gear quality issues as you would see on a worm drive system like the Evolution.

 

 

Best regards,
Mike Swanson
https://www.NexStarSite.com



#14 Ddaniel84

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Posted 27 July 2020 - 12:34 AM

I've plane to follow a course on autoguiding (PHD2) and tracking images at beginning of september. Today exposures are limited to one min. My goal is to reach 2 or 3 minutes.
Your answer let me think that it's possible with C8Ev. Otherwise I think to change it for an equatorial mount. Is there anither alternative to reach so accuracy in tracking?
Dom

#15 Michael_Swanson

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Posted 27 July 2020 - 12:40 AM

You should be able to get 2-3 minute exposures once you get the autoguiding all worked out.

 

Best regards,
Mike Swanson
https://www.NexStarSite.com



#16 Ddaniel84

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Posted 27 July 2020 - 01:33 AM

🙏👍

#17 Ddaniel84

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Posted 27 July 2020 - 01:34 AM

🙏👍

#18 lov2krz

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Posted 27 July 2020 - 02:30 PM

I'm very happy to have found this thread.  My alignment reference register is full and I  want to know how to overwrite, delete and replace them.

 

I have a Celestron GEM DX mount with an 11" Edge HD in my NexDome with StarSense.  The SS sits on Losmandy dovetail on top of and at the front of the OTA to give the camera a wide open view of the sky through the dome slit.  The SS sits on the dovetail bar using an ADM DV Series Dovetail Adapter for StarSense Mounting; for reference only. I have updated the SS firmware a few weeks ago.  The mount and OTA are well-balanced.

 

Here is my process:

1.  I manually set the home position to the reference marks on the mount and set the HC Axis Positions to 90.00.00. 

2.  I then Polar Aligned (PA) the mount using Pole Master (PM) as close a humanly possible to align the green square over the red circle in the monitoring phase of the PM PA.  I triple checked the PA alignment to ensure I was really PA on the NCP and could not get any closer star monitoring alignment using PM.

2a.  I reset the Axis Positions to 90.00.00 from a few arc seconds off from step 1.

3.  I did an auto alignment with SS and calibrated the camera to the mount and then repeated the auto align. 

3a.  I added 6 alignment reference images and got dead on goto and auto guiding for my first 3 targets.  During the next slew the mount hit the RA limit, so I hit the back button and selected another target.  When the scope slewed to the new target it was nowhere near the center of my 38 mm EP. 

4.  I sent the mount to the home position and the DEC axis was lined up to the reference marks but the RA was off by ~15 degrees west.

5.  I unlocked the RA axis and set back to the reference marks.

6.  I did another goto slew and the target was no longer in the EP FOV.

7.  I tried to add another reference point but got the message about already having 10 images.

8.  I sent the mount to home and put it into hibernate then powered down the mount.

 

I'm looking for some help to delete or replace some alignment reference images and if I should try a Sync Reference.

 

Any help is greatly appreciated.

Steven



#19 Ddaniel84

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Posted 27 July 2020 - 04:10 PM

Hi Steven I experiment sometimes the same situation. What I did then was delete the alignment and began from scratch.
The good news is that the new version of CPWI (2.3.5) now well manage slew limits. The physical altitude limit for my C8 is -30°. Until now CPWI 2.3.4 always force it to 0!
Perhaps it can be a part of the answer...
Dominique

#20 lov2krz

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Posted 27 July 2020 - 06:15 PM

Dominique, thanks for letting me know.  I really took my time getting those additional reference images but I knew I'd have to start over.  This time I'm going to save the alignment.

 

Steven 




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