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Is all star polar align exclusive to Celestron?

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#1 Darren Drake

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Posted 06 July 2020 - 05:39 PM

I recently got a CGEM II and love this new feature.  I'm new to eq mounts being  a dob guy so i had the impression that this is such a cool feature that it must be in other mounts.  However i havent found any that  allow polar alignment by offsetting any star the same amount as the polar alignment error.  So i wonder if other mounts have this.  And if not why not?  Is it patented?


Edited by Darren Drake, 06 July 2020 - 05:41 PM.


#2 Michael Covington

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Posted 06 July 2020 - 06:05 PM

I can tell you iOptron definitely does not.   I am told Losmandy Gemini does but am not sure.  The other brand to check would be Sky-Watcher, which is likely to be similar to Celestron, but I'm not sure.

I'm wondering if it's patented, too!  Seems like it might be too obvious to be patentable.



#3 DuncanM

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Posted 06 July 2020 - 09:07 PM

I recently got a CGEM II and love this new feature.  I'm new to eq mounts being  a dob guy so i had the impression that this is such a cool feature that it must be in other mounts.  However i havent found any that  allow polar alignment by offsetting any star the same amount as the polar alignment error.  So i wonder if other mounts have this.  And if not why not?  Is it patented?

 

iOptron implements a similar feature.

 

"5.3.6. Polar Iterate Align
This alignment method allows you to polar align the mount even if you cannot view the Celestial Pole.
Press the MENU button, then select “Alignment” and “Polar Iterate Align”. The HC will display a list of
bright alignment stars near the meridian as Alignment Star A. Follow the HC instructions to move
Alignment Star A to the center of the eyepiece using a combination of the Latitude Adjustment Knob
and the “◄” and “►” buttons. Press ENTER to confirm the settings. Next, select a bright star that is
close to the horizon as Alignment Star B. Center it using the Azimuth Adjustment Knobs and the “◄”
and “►” buttons (the “▲” and “▼” buttons will not function). Press ENTER to confirm the settings.
The telescope will now slew back to Alignment Star A to repeat the above steps. The iteration can be
stopped when it is determined that the alignment error has been minimized. Press the BACK button to
exit the alignment procedure.
NOTE: It is highly recommended to use an eyepiece with illuminated crosshairs for accurate centering.
NOTE: The movement of the alignment star in your eyepiece may not be perpendicular depending on
its location in the sky." (page 29 of the CEM60 manual)

 

But I've never used it, so I can't speak to the accuracy of it. IIRC, Synta/Orion Syncan mounts have a similar feature.


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#4 Michael Covington

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Posted 06 July 2020 - 09:19 PM

In my limited experience, iOptron's Polar Iterate Align apparently relies on the accuracy of the starting position.  Celestron's ASPA does not; it uses the model that is built by syncing on up to 6 stars.

 

I could be wrong; I haven't totally worked out the mathematics of Polar Iterate Align; but it seems to me that with only two stars, it is vulnerable to errors in the starting position in declination.  You should "Search Zero Position" beforehand, to go to the starting position that is marked by a hardware sensor.  But I doubt that this has arc-minute accuracy.



#5 DuncanM

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Posted 06 July 2020 - 09:26 PM

In my limited experience, iOptron's Polar Iterate Align apparently relies on the accuracy of the starting position.  Celestron's ASPA does not; it uses the model that is built by syncing on up to 6 stars.

 

I could be wrong; I haven't totally worked out the mathematics of Polar Iterate Align; but it seems to me that with only two stars, it is vulnerable to errors in the starting position in declination.  You should "Search Zero Position" beforehand, to go to the starting position that is marked by a hardware sensor.  But I doubt that this has arc-minute accuracy.

 

The CEM60 manual suggests doing a 2 or 3 star alignment first.


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#6 Starlancer

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Posted 06 July 2020 - 10:37 PM

Sky Watcher AZ-GTI has this feature in the phone app.  It's really nice and works pretty well, to bad the mount is questionable, at least for photography, but not bad for visual.



#7 freestar8n

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Posted 06 July 2020 - 10:38 PM

I think Bisque  has something similar now but I believe it was added after ASPA.

 

There may have been similar things before ASPA but they didn't get much attention - and if they relied on a sky alignment with only 2 or 3 stars they would have had limited accuracy.

 

As for it being obvious - I think the concept is obvious but there is good indication the implementation is not obvious.  This is shown by my trials and tribulations in CN trying to convince people the procedure needs to assume the mount is level.  The fact that so many people think it can be done without assuming level is direct indication the implementation is not obvious.

 

Unfortunately the procedure is still described as slow compared to some other recent methods - but it is unique in being combined with the sky alignment process, whereas other procedures require a complete sky alignment *after* polar alignment.  With ASPA the two proecedures are combined so polar alignment does not add much time.

 

Frank


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#8 Michael Covington

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Posted 07 July 2020 - 08:23 AM

Yes, this turns out to be one of the situations where levelness matters -- because ASPA assumes azimuth is really azimuth and altitude is really altitude -- which means it assumes the mount is level.   At the same time, didn't we establish that the effect of errors in levelness is small, and the procedure still converges to an accurate solution if you do it more than once?  (I always do it more than once to make sure it succeeded.)



#9 freestar8n

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Posted 07 July 2020 - 08:30 AM

Yes it’s a small effect as long as it is reasonably level. But most people thought level was completely irrelevant and the mount could be upside down since it “knows” where the pole is. And that says they would not know how to implement it - and it therefore isn’t obvious how to do it.

Frank
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#10 OldManSky

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Posted 07 July 2020 - 12:34 PM

While ASPA is indeed "cool," it's a somewhat expensive add-on, and a "one-trick pony"; hardware that only really does one thing.

Since many of us guide our mounts, or have cameras on the main scopes, a $15 license for Sharpcap Pro can use your guide/main scope and camera to do essentially the same thing, without having to have specialty hardware to do only polar alignment.  If you already have a guide scope or camera attached to your main scope, Sharpcap is the bomb.  PHD2 also has basically "analyze then show an interactive display to move a star to a position" polar alignment, using hardware you already have -- and it's completely free :)



#11 rmollise

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Posted 07 July 2020 - 01:01 PM

Other than Celestron and the other Synta brand SkyWatcher (Synscan), no. But there are many similar implementations.

 

However, most find it quicker and easier to do a precise polar alignment with Sharpcap or Polemaster these days.



#12 mclewis1

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Posted 07 July 2020 - 01:33 PM

While ASPA is indeed "cool," it's a somewhat expensive add-on, and a "one-trick pony"; hardware that only really does one thing.

?? I think you are referring to StarSense or perhaps one of the other vendors polar alignment tools?

 

ASPA is the built in polar alignment routine in the NexStar hand controller firmware ... no extra cost, no hardware involved, etc.


Edited by mclewis1, 07 July 2020 - 01:34 PM.

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#13 EFT

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Posted 07 July 2020 - 03:59 PM

I thought that the more recent hand controller/firmware Synscan mounts had a similar routine to that of the ASPA but maybe I'm wrong about that.  Considering that the Synscan and Nexstar mounts are made by the same company, it wouldn't be surprising if they had similar or identical routines.  A variety of companies use internal polar alignment routines now in order to avoid the old drift-alignment method with some better than others.  I doubt that there would be any patent or copyright on this or, if there was, you couldn't get around it by developing a different routine.


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#14 eyeoftexas

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Posted 07 July 2020 - 05:08 PM

Other than Celestron and the other Synta brand SkyWatcher (Synscan), no. But there are many similar implementations.

 

Shouldn't Orion have this ability too, since it uses Synscan?  



#15 DuncanM

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Posted 07 July 2020 - 05:22 PM

Shouldn't Orion have this ability too, since it uses Synscan?  

It does, this is from the Orion Synscan 5 HC manual:

 

"6.8 Polar Alignment without Polar Scope
Polar alignment of your mount by means of the polar-axis scope
is covered in the instruction manual for the mount.
However, there is another, more accurate way to polar align.
This software-based polar alignment routine can be performed
without use of the polar-axis scope. You will need to use a reticle eyepiece for this procedure to ensure precise centering of
the stars in the eyepiece field of view.
1. Complete a 2-star alignment or 3-star alignment. At the
end of the alignment, the SynScan hand controller will
display the polar alignment error in altitude (Maz) and
azimuth (Mel) (refer to Section 5.17). Based on the error
given, you can decide whether it will be necessary to
adjust the polar alignment.
2. Press the “MENU” shortcut key, and then access to submenu “Alignment\Polar Alignment”. Press the ENTER key
to proceed to the next step.
3. The screen will display “Select a Star”.
• Use the scroll keys to browse through a list of star
names and press the ENTER key...
"

 

It goes on to describe a similar process as used on the iOptron mounts.

 

However, IMHO and experience, a well aligned PAS used carefully, is just as accurate as software assisted PA.


Edited by DuncanM, 07 July 2020 - 05:24 PM.


#16 eyeoftexas

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Posted 07 July 2020 - 05:25 PM

Thanks, good to know.  I'm considering a new, larger GEM, so it's nice to know what various can and cannot do.



#17 OldManSky

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Posted 07 July 2020 - 06:27 PM

?? I think you are referring to StarSense or perhaps one of the other vendors polar alignment tools?

 

ASPA is the built in polar alignment routine in the NexStar hand controller firmware ... no extra cost, no hardware involved, etc.

You're correct, I did indeed confuse ASPA for the StarSense add on.  Thanks for pointing out the error.



#18 descott12

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Posted 07 July 2020 - 06:37 PM

You're correct, I did indeed confuse ASPA for the StarSense add on.  Thanks for pointing out the error.

But your comment about using SharpCap for PA couldn't be more true. It is amazing. My very first polar alignment ever  was done in about 5 minutes using a guide scope and SharpCap.


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#19 mclewis1

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Posted 08 July 2020 - 06:05 PM

It's a good point Dave (and Paul), the polar alignment tool in SharpCap does also work well. There are actually quite a few software based tools as well as a number of hardware add ons. We sure have come a long way from the only options of a polar alignment scope or drift alignment for polar alignment.


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#20 jdupton

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Posted 08 July 2020 - 06:24 PM

Dave & Mark,

 

   I do not use SharpCap but was under the impression that it requires visibility of the polar area in order to work.

 

   That is one of the things that may be important to some. The Celestron ASPA and the SkyWatcher / SynScan counterpart work anywhere in the sky and do not require the pole area to be visible. I would expect SharpCap to be a bit better with respect to accuracy but if you cannot see the pole, the ASPA method would be the next best thing.

 

 

John



#21 descott12

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Posted 08 July 2020 - 06:42 PM

Dave & Mark,

 

   I do not use SharpCap but was under the impression that it requires visibility of the polar area in order to work.

 

   That is one of the things that may be important to some. The Celestron ASPA and the SkyWatcher / SynScan counterpart work anywhere in the sky and do not require the pole area to be visible. I would expect SharpCap to be a bit better with respect to accuracy but if you cannot see the pole, the ASPA method would be the next best thing.

 

 

John

Hmmm... you may have a point. The SC routine uses stars in the vicinity of Polaris but I am not sure how far away it would work. I have only used it the one time so others with more experience may know for sure.



#22 mclewis1

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Posted 08 July 2020 - 07:15 PM

Yes the SC polar routine does require a view of the polar area (as well as a camera), as do most of the other choices. Celestron/Synta's built in ASPA routine is certainly in some ways a step beyond this but it doesn't have a plate solving component as the SC routine does. It's a bit of apples to oranges, and a number of the other solutions each have little additional benefits, quirks, or drawbacks.



#23 Darren Drake

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Posted 08 July 2020 - 08:39 PM

The ASPA feature also has the advantage of being possible to accomplish in strong twilight when only a few bright stars are visible saving  precious time or if its cloudy in the northern sky ...


Edited by Darren Drake, 08 July 2020 - 08:40 PM.

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#24 freestar8n

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Posted 09 July 2020 - 03:44 AM

All these methods have their advantages, but I think only ASPA and drift alignment can be done with a blocked view of the sky around the pole.

 

And only ASPA allows good goto accuracy immediately after polar alignment is completed.  It may not be perfect, but the mount knows the initial sky alignment so it can have good goto - and then you do ASPA - and when done the mount knows it is polar aligned and can adjust the original sky model accordingly.  It may not be perfect, but it isn't completely blind as it is when using a device to polar align without also building a sky model for good goto.

 

But times have changed, and for imagers with plate solving there is less need for good goto accuracy.  Just getting it polar aligned and then using a simple model that assumes the mount is level and longitude/time are accurate should get them close - and a plate solve based centering routine should center to the desired accuracy.

 

For a permanent setup none of this matters and you can take your time once to get it aligned.  So these methods mainly focus on mobile or temporary setups.  In that case being able to do it at dusk is important for saving time.

 

I think the main thing to keep in mind is there are many factors involved and "time to polar align" by itself may not be so important.

 

Frank


Edited by freestar8n, 09 July 2020 - 03:44 AM.

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#25 OldManSky

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Posted 09 July 2020 - 10:43 AM

The ASPA feature also has the advantage of being possible to accomplish in strong twilight when only a few bright stars are visible saving  precious time or if its cloudy in the northern sky ...

Same with iOptron's iterative polar alignment -- which also doesn't require a view north, and lets you work as soon as bright stars are visible :)




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