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Getting the most of iPolar

Polar Alignment
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#1 jlecomte

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Posted 14 May 2021 - 09:57 PM

Hi everyone,

 

I hope this will be helpful to some of you who use iOptron’s iPolar.

 

I found a way to greatly improve the accuracy of iPolar (I have a CEM70, but the following can probably be applied to other mounts). The idea is to measure the center coordinates multiple times (e.g. 10 times) with the mount in various orientations (this is important), average all the coordinates, and finally enter the average value for X and Y manually in the iPolar software settings. Additionally, for each measurement, after confirming position 1 and before moving to position 2, put your hand in front of the iPolar camera and rotate the RA axis manually, about 45°. As soon as you remove your hand, the iPolar software will confirm position 2. If you don’t put your hand in front of the camera, the iPolar software will confirm position 2 almost immediately, with a very small rotation angle, which likely reduces the accuracy. With this, and a properly executed polar alignment, I was able to take fairly long unguided exposures with minimal star trailing (only the periodic error, along the RA axis, shows up in unguided exposures, which obviously can be fixed with PEC to some extent, or with guiding) Also, the Go-To accuracy is incredible!

 

Hope this helps!

Julien

 

Note: I use iPolar software version 2.50 (latest version at the time of this writing)


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#2 niccoc1603

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Posted 15 May 2021 - 01:47 AM

I have also noticed that v 2.50 confirms position 2 almost immediately and as a result I got horrible PA alignment accuracy in PHD. I then switched back to 2.21 and this version allows for a larger rotation of the mount before it automatically picks position 2, PA alignment accuracy went back to very good sub 1' values.

I'll try the averaging, it definitely sounds like a good point.



#3 PaulE54

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Posted 15 May 2021 - 04:11 AM

Agree, this sounds really helpful. I'll have to give this a go if the clouds ever clear :-)

 

Paul



#4 alphatripleplus

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Posted 15 May 2021 - 07:35 AM

Interesting idea. Can you quantify how much of an improvement this makes in polar alignment, e.g. going from 5 arcmins to 2 arcmins?



#5 iwannawon

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Posted 15 May 2021 - 01:25 PM

i have a cem70 and haven't had issues, mostly because i'm guiding. but i'm still interested in understanding how to make the initial PA better. it's packed up so i can't easily look at the UI at the moment so can you clarify/expand on what you mean by 'measure the center coordinates' and 'enter the average value for X and Y manually in the iPolar software settings'? what are you measuring and with what? where are you entering them? thanks.



#6 GaryShaw

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Posted 15 May 2021 - 01:45 PM

i have a cem70 and haven't had issues, mostly because i'm guiding. but i'm still interested in understanding how to make the initial PA better. it's packed up so i can't easily look at the UI at the moment so can you clarify/expand on what you mean by 'measure the center coordinates' and 'enter the average value for X and Y manually in the iPolar software settings'? what are you measuring and with what? where are you entering them? thanks.

exact same question... I have version 2.5. 

Gary



#7 MountainAir

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Posted 15 May 2021 - 02:35 PM

i have a cem70 and haven't had issues, mostly because i'm guiding. but i'm still interested in understanding how to make the initial PA better. it's packed up so i can't easily look at the UI at the moment so can you clarify/expand on what you mean by 'measure the center coordinates' and 'enter the average value for X and Y manually in the iPolar software settings'? what are you measuring and with what? where are you entering them? thanks.

  1. Do your initial calibration.  Record the X/Y coordinates of the center of the sensor in a spreadsheet.  This is shown in the software after you finish calibration.
  2. Do another calibration (by clearing the x/y center via the button in the software), putting the RA axis at a different position.  Record the X/Y in a new row in the spreadsheet.
  3. Repeat at least 4 times (no more than 10).
  4. Average all the X pixel coordinates in one column, then all the Y pixel coordinates in another column.
  5. Input that X/Y manually into iPolar.  Congratulations, you've just almost eliminated the effects of seeing!

This will improve your PA accuracy, but don't expect miracles because the PA error likely isn't bad with just the standard single calibration.  I have four iPolar cameras now.  Even with a single calibration, I have NEVER seen PA alignment error greater than one arc-minute when compared to SharpCap, KStars or PHD2 polar alignment error values.  Most of my cameras were within 30 arcsec of those other software packages.  I think iPolar is a fantastic hardware product and concept, with somewhat poor software.  When I was new at this, using Celestron's All-Star-Polar-Alignment, it could spend an HOUR trying to get a really good PA.  With iPolar it takes me 90 seconds.

 

Edit:  I actually posted this procedure in more detail here:  https://www.cloudyni...7#entry11084375

 

Here's the Mac version, showing the Input Center of Camera and Clear Center of Camera buttons, and the X/Y values the calibration procedure produces.  These are blank in mine because I was not connected to my camera when I grabbed the screen shot.

 

Screen Shot 2021-05-15 at 12.38.24 PM.png


Edited by MountainAir, 15 May 2021 - 02:40 PM.


#8 GaryShaw

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Posted 15 May 2021 - 03:04 PM

Thanks! 
what exactly are the x and y numbers ?

does entering a number reset the PA somehow!

Gary



#9 GaryShaw

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Posted 15 May 2021 - 03:42 PM

Sorry, but after reviewing the manual several times, I'm unclear on what you mean by calibration. That term does no appear in the manual. Do you mean the 'position 1' confirmation?

 

Also, what do you mean when saying you rotated the iPolar camera to be orthogonal to the ground?

Thank you,

Gary


Edited by GaryShaw, 15 May 2021 - 03:50 PM.


#10 MountainAir

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Posted 15 May 2021 - 10:53 PM

Thanks! 
what exactly are the x and y numbers ?

does entering a number reset the PA somehow!

Gary

The X and Y numbers represent the center of rotation on the iPolar camera's sensor.  When the iPolar software asks you to confirm position 1/2/3, it is plate solving the stars in each image and calculating the center of rotation of the mount, which is translated to the X/Y coordinates on the camera sensor.

 

Sorry, but after reviewing the manual several times, I'm unclear on what you mean by calibration. That term does no appear in the manual. Do you mean the 'position 1' confirmation?

 

Also, what do you mean when saying you rotated the iPolar camera to be orthogonal to the ground?

Thank you,

Gary

The "confirm position 1", "confirm position 2" etc. is the calibration process.  My apologies for not using terminology that matches the manual, but it's been over a year since I've looked at it.

 

Regarding the orientation of iPolar... It is best to use iPolar when the sensor is either parallel to or perpendicular to the ground.  If the sensor is diagonal, such as if the camera was installed at an angle (which some people have reported) or in some devices like the SkyGuider Pro where the axis can turn completely around, then when you try to adjust your ALT-AZ knobs to center the circle on the cross things will move diagonally.  It's perfectly possible to get a good polar alignment this way, but it's just not very natural and can be really frustrating for new users.  It's best if moving AZ knobs only moves the circle left or right, and if moving the ALT knobs only moves the circle up and down.  It makes for a much faster polar alignment in my experience.  For this same reason, when doing the calibration process it's best to start from the home position with the counterweights straight down (hopefully the sensor is parallel to the ground in this position).  If you've already confirmed positions, then your adjustments will move in predictable ways.  If you do the "confirm position" process and you end up with your RA shaft at 90 degrees, you again won't be diagonal to the ground -- which is good.  in this case the ALT knobs will move left and right, and the AZ knobs will move up and down, but it'll still be much easier than moving diagonally.


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#11 GaryShaw

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Posted 16 May 2021 - 09:33 AM

Thanks Mountainair…

 

I examined the camera and it’s mounting location and see some screws that may have something to do with adjusting it but have no way to know when it’s level other than trial and error which will waste a lot of observing time. Any clues you can offer on how to straighten the camera in daylight without a lot of trial and error?  
 

thank you

Gary



#12 jlecomte

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Posted 16 May 2021 - 09:06 PM

@GaryShaw The point of iPolar calibration is that you do NOT have to align anything. You only have to make sure that those two set screws, which hold the iPolar camera against the inside of the RA axis (on a CEM70 at least) are tight, so that you can be confident that a single calibration will be needed and you can reuse it for a long time.

#13 jlecomte

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Posted 16 May 2021 - 09:07 PM

Folks, a lot of people already knew about averaging multiple measurements for the center position. What I added here is a simple technique you can use to get a larger angle between position 1 and 2, thereby leading to a slightly more accurate measurement.

#14 MountainAir

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Posted 17 May 2021 - 10:00 PM

Thanks Mountainair…

 

I examined the camera and it’s mounting location and see some screws that may have something to do with adjusting it but have no way to know when it’s level other than trial and error which will waste a lot of observing time. Any clues you can offer on how to straighten the camera in daylight without a lot of trial and error?  
 

thank you

Gary

On my SkyGuider Pro, you can see the lettering and USB port on the back of the camera. If those are parallel to the ground, you're good.  On most other mounts, though, you can't see the back of iPolar.  If the grub screws on the lens side of iPolar look like they are at the 0° and 90° positions, I think that also works.  I just installed one in a CEM120EC2 and those two grub screw positions were perfect (but I don't know about other mounts).  Most iOptron mounts probably had iPolar installed very straight, so you probably won't need to worry about this.  One way to test it is with your counterweights down, adjust your AZ knobs; if the image moves diagonally, your sensor isn't straight.

 

But again, this orientation of iPolar has nothing to do with how accurate it is.  It only affects whether your ALT-AZ adjustments work orthogonally to the axis you're adjusting, or diagonally to it.  An iPolar that's parallel or perpendicular to the ground just makes adjusting those ALT-AZ knobs a bit easier.

 

And yes, as jlecomte said definitely cover iPolar before clicking the OK button after you confirm position 1.  It's more than slightly more accurate, it's potentially a LOT more accurate when you have adequate movement of RA between the two/three confirmed positions.  I think this is fairly well-known, though, because often the darn thing will confirm position 2 right at position 1.  The software didn't used to do that.


Edited by MountainAir, 17 May 2021 - 10:02 PM.

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