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Review of iPolar hardware and software for polar alignment

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#1 stephen.kennedy

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Posted 05 December 2020 - 01:42 PM

iOptron’s iPolar upgrade, which replaces the optical scope on the iOptron SkyGuider Pro, does not accurately provide polar alignment when compared to results measured using identical equipment operating Sharpcap Pro and the specified guide camera and scope. Data was collected while simultaneously running both the iPolar alignment software and SharcapPro on the same equipment. The deficiency is consistent with an issue in the iPolar system’s calculation of altitude parameters in polar alignment after plate solving.

Click here to view the article

#2 pbealo

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Posted 05 December 2020 - 02:02 PM

SharpCap report shows how to move polar axis to be dead on north. The units are degrees, minutes and seconds of arc. Your screen shot showing 0.1.39 means you're off of north by 1 minute 39 sec. Not bad at all. A minute is 1/60th of a degree. And basically all of your error can be eliminated by moving axis too right by that amount. 5 sec down is basically nothing.

 

When SharpCap shows the error of 1.00.00 it means you're off by a degree, or twice the diameter of the moon.


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#3 barrabclaw

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Posted 06 December 2020 - 08:40 PM

Have you tried re-calibrating iPolar? (two exposures at different rotations about the RA axis).

 

If that doesn't work, you can manually set the center position. I did this same comparison with SharpCap and manually & iteratively adjusted the "center of camera" position until both pieces of software gave very similar results.


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#4 Linwood

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Posted 06 December 2020 - 09:35 PM

Besides the good question above, I did not see anything in your article that supports the conclusion that this is an error in calculation of atmospheric effects. I am not saying it is not, just that I saw no support for that statement. 

 

I will say that on both the CEM40 and CEM70 I have found the alignment to be within anywhere from 1-5 arc minutes in most cases, without any significant effort, just get the plus pretty close to centered in the circle. 


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#5 stephen.kennedy

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Posted 07 December 2020 - 12:04 PM

Have you tried re-calibrating iPolar? (two exposures at different rotations about the RA axis).

 

If that doesn't work, you can manually set the center position. I did this same comparison with SharpCap and manually & iteratively adjusted the "center of camera" position until both pieces of software gave very similar results.

Thank you for your comment. This will confirm that troubleshooting included recalibration of the iOptron polar alignment system on three separate occasions with no observable improvement. As for manually and iteratively adjusting the center of camera position, the purpose of the review was to evaluate the product from the factory after calibration and advise potential users of how well the product performs when compared to a polar alignment product known to be reliable. The scope of the review was not to determine whether the user can modify the product to make it work within specifications, but rather, to review the product out of the box. Manual modifications of the camera could void warranties associated with the product, however, I have not analyzed the specifics of the warranty. For products out of warranty, a forum post advising how to manually adjust the center of camera position may be of value. 



#6 barrabclaw

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Posted 07 December 2020 - 01:17 PM

Thank you for your comment. This will confirm that troubleshooting included recalibration of the iOptron polar alignment system on three separate occasions with no observable improvement. As for manually and iteratively adjusting the center of camera position, the purpose of the review was to evaluate the product from the factory after calibration and advise potential users of how well the product performs when compared to a polar alignment product known to be reliable. The scope of the review was not to determine whether the user can modify the product to make it work within specifications, but rather, to review the product out of the box. Manual modifications of the camera could void warranties associated with the product, however, I have not analyzed the specifics of the warranty. For products out of warranty, a forum post advising how to manually adjust the center of camera position may be of value. 

Manually adjusting the center position of the camera is done in software. Basically, telling the software which pixel is at the center of rotation. Definitely not modifying the product or voiding a warranty. It's a feature built into the software.

 

Edit: Setting the center position is exactly what the 2-image calibration does. But you can tweak it by a few pixels manually (in the software) to make it more accurate.


Edited by barrabclaw, 07 December 2020 - 01:18 PM.

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#7 Linwood

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Posted 07 December 2020 - 01:50 PM

Re center that begs another question: Can an iPolar be installed (from the factory) somewhat off-axis?  Wouldn't that lead to bad alignment?   And if so -- other than bad alignment, how would one tell? 

 

Unfortunately it does all sorts of filtering out non-stars, otherwise you could do something like swing it through 180 degrees while taking a photo and look at the star trails. If it's off axis, would there even be a non-moving center? 

 

Note this does not negate the findings of the review, since if true it is clearly a problem with the iPolar (at least as installed).  I'm just curious if there is a way to find out definitively WHY it is performing so badly for the author?  Not just that it is. 



#8 stephen.kennedy

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Posted 07 December 2020 - 06:06 PM

Manually adjusting the center position of the camera is done in software. Basically, telling the software which pixel is at the center of rotation. Definitely not modifying the product or voiding a warranty. It's a feature built into the software.

 

Edit: Setting the center position is exactly what the 2-image calibration does. But you can tweak it by a few pixels manually (in the software) to make it more accurate.

Thank you for the clarification. I understood the phrase "manually and iteratively adjusting the center of the camera position" to mean a repetitive process of physically adjusting the position of the camera, which would could void the warranty. The software provides for 2-image calibration which was an exercise completed on three occasions to no effect. Other than the 2-image calibration, no other modifications were attempted to compensate for the deficiency. The purpose of the review was to compare the functionality of the iPolar alignment system from a factory-installed SkyGuider Pro when compared to a software product that uses a third party guide camera and scope attached to the same mount.



#9 barrabclaw

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Posted 07 December 2020 - 09:27 PM

Re center that begs another question: Can an iPolar be installed (from the factory) somewhat off-axis?  Wouldn't that lead to bad alignment?   And if so -- other than bad alignment, how would one tell? 

 

Unfortunately it does all sorts of filtering out non-stars, otherwise you could do something like swing it through 180 degrees while taking a photo and look at the star trails. If it's off axis, would there even be a non-moving center? 

 

Note this does not negate the findings of the review, since if true it is clearly a problem with the iPolar (at least as installed).  I'm just curious if there is a way to find out definitively WHY it is performing so badly for the author?  Not just that it is. 

An offset of the axis of the electronic polar scope from the RA axis is what the calibration accounts for. If the scope was installed perfectly, there wouldn't be a need for calibration. With the scope offset from the RA axis, the star trails will rotate around a point that isn't the center of the sensor. The calibration procedure finds the pixel that it is at the center of rotation. I did the calibration and then polar aligned with SharpCap. Switch back to iPolar, notice it's not perfect, type in a new center position a pixel or two in the correct direction. Rotate around the RA axis to make sure it's stable at any angle.

 

You can also do this procedure without SharpCap and basically perform the calibration procedure on your own. Rotate around RA, visually see where the point it thinks is center rotates around, and adjust the center position until you bring the two into alignment. (I'm not talking about where it thinks north is, just where it thinks the center is compared to where you see the center is)

 

No idea why it's performing poorly for Stephen. I've noticed that the iPolar calibration will sometimes try to take the second image really quickly after I just barely move the RA axis. Calibration will be less accurate if the two images are only a few degrees apart. The software should wait for you to tell it that you're ready for it to take a second image, but it doesn't. I agree that the iPolar software could use some work, especially to make it work quickly right out of the box.

 

Stephen, let's say you have it polar aligned according to iPolar. What happens when you rotate 90 deg around RA? Does it go out of agreement? And what happens if you go another 180, so 90 deg the other way from the starting position? I'll be it drifts around, which would mean the center position is off in the software.

 

 

Another issue could be sag in the main scope with respect to the mount. In that case, the mount could be well-aligned, but SharpCap would give a different answer. I doubt that's the case for Stephen, as he saw star trails when aligned with iPolar but no trails when aligned with SharpCap.



#10 Linwood

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Posted 07 December 2020 - 09:34 PM

An offset of the axis of the electronic polar scope from the RA axis is what the calibration accounts for. If the scope was installed perfectly, there wouldn't be a need for calibration. With the scope offset from the RA axis, the star trails will rotate around a point that isn't the center of the sensor. The calibration procedure finds the pixel that it is at the center of rotation. I did the calibration and then polar aligned with SharpCap. Switch back to iPolar, notice it's not perfect, type in a new center position a pixel or two in the correct direction. Rotate around the RA axis to make sure it's stable at any angle.

 

I'm having trouble visualizing it, but I was not thinking offset, but not aligned.  In other words, a line from the center of the lens to the center of the sensor may not be in the center of the axis, but it is parallel.  What if instead it isn't, what if when the axis were polar aligned perfectly the whole iPolar assembly were pointing left 5 degrees or some such.  I'm not sure the centering procedure can deal with that (I'm not sure it cannot either, as I said, having trouble visualizing it). 

 

 

Another issue could be sag in the main scope with respect to the mount. In that case, the mount could be well-aligned, but SharpCap would give a different answer. I doubt that's the case for Stephen, as he saw star trails when aligned with iPolar but no trails when aligned with SharpCap.

Is that true?  I thought if the axis of the mount were properly aligned, that a mis-aligned scope still would track properly and drift align as polar aligned properly.  



#11 barrabclaw

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Posted 07 December 2020 - 10:21 PM

I'm having trouble visualizing it, but I was not thinking offset, but not aligned.  In other words, a line from the center of the lens to the center of the sensor may not be in the center of the axis, but it is parallel.  What if instead it isn't, what if when the axis were polar aligned perfectly the whole iPolar assembly were pointing left 5 degrees or some such.  I'm not sure the centering procedure can deal with that (I'm not sure it cannot either, as I said, having trouble visualizing it). 

So do you mean what if the axis of the iPolar is at an angle to the RA axis of the mount?

 

Is that true?  I thought if the axis of the mount were properly aligned, that a mis-aligned scope still would track properly and drift align as polar aligned properly.  

I mean that the flexure changes with rotation. So not just misaligned, but changing as you move around the axis. For example, if you're at 90 degrees, a heavy scope on a weak mounting could bend down a bit. But then as you come up to 0 degrees, there's no bending. And between 0 and 90, the bend is somewhere in between. In this case, where SharpCap directs you for polar alignment would be different depending on which angles you used for the before and after positions. If you have a very rigid setup and the misalignment is constant throughout the range of rotation, I think you're right.


Edited by barrabclaw, 07 December 2020 - 10:22 PM.


#12 Linwood

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Posted 07 December 2020 - 10:26 PM

So do you mean what if the axis of the iPolar is at an angle to the RA axis of the mount?

Correct.  Basically the iPolar is a semi-cylinder that fits inside of a tube, and I think iOptron depends on the tube holding the iPolar along the same axis.  What if it got in kind of cockeyed somehow.   What would the impact be, or would it just magically work out? 


Edited by Linwood, 07 December 2020 - 10:30 PM.


#13 barrabclaw

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Posted 07 December 2020 - 10:54 PM

Correct.  Basically the iPolar is a semi-cylinder that fits inside of a tube, and I think iOptron depends on the tube holding the iPolar along the same axis.  What if it got in kind of cockeyed somehow.   What would the impact be, or would it just magically work out? 

I'm not sure. I kind of think it would work out, just like a main scope that is slightly misaligned. Cylinders are pretty easy to machine, though, and if it runs the length of the mount, how big of an angle could it reach, even with a little play?



#14 Linwood

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Posted 07 December 2020 - 11:08 PM

Just grasping at straws in terms of the OP's problems.

 

I'm not completely convinced.  I get how a main scope doesn't matter, but that's because the axis of rotation is aligned.  In this case it's to get the axis aligned.  But I don't know. 



#15 barrabclaw

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Posted 07 December 2020 - 11:25 PM

However the iPolar scope is aligned, it should rotate around the mount's RA axis. Hopefully, the axis of the iPolar is perfectly aligned with the RA axis. If it is angled, it will still rotate around the RA axis, but that will swing the iPolar about the RA axis. Like two chopsticks glued together at an angle, and you rotate one while holding it otherwise motionless. The other will swing around it. Like here, where P1 is the axis of the iPolar.

 

axisAngle1.png

 

In the case that they are aligned but the iPolar is translated, it would look like this, where B is the iPolar and Q is the RA axis.

 

FixedAxis.png

 

If you have both...idk, just use SharpCap! laugh.gif  

 

 


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#16 MHamburg

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Posted 08 December 2020 - 12:08 PM

I can only relate my own recent experience with the iPolar. I have an AP900 GTO mount permanently installed in my observatory. I retrofitted the iPolar camera with the recommended adapter. At first, I found the software to be rather "jumpy." I later learned that much of the jumpiness was due to strong atmospheric refraction. Later I achieved excellent PA and found that guiding at 2800mm with my Edge 11HD and a Lodestar through an OAG, PHD2 called for only small  corrections. I took 35 180s subs with no trace of any trailing stars. Just sayin'

Michael

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Edited by MHamburg, 08 December 2020 - 12:21 PM.


#17 Linwood

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Posted 08 December 2020 - 01:36 PM

@barrabclaw, ok, I think i'm convinced.  The center calculation will always be a center of rotation, so as long as the iPolar remains at whatever cant it is calibrated at, it should still polar align.

 

It would be interesting to know why it wasn't working for the OP.  What could iOptron have done incorrectly in that one?   

 

I looked at my guiding assistant runs from last night, and did two separate GA runs (was testing backlash really), east and west of meridian, one said 1.6' off, one 3' off.  That's consistent with every attempt; I can't imagine how to get a full degree off.  Something was clearly broken on the OP's.


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#18 mborland

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Posted 10 December 2020 - 01:09 AM

I use factory-installed iPolar units in my CEM60 and CEM40EC. After polar-aligning using the iPolar software, I use the PHD2 Guiding Assistant to check the polar alignment. For the CEM60, I routinely get less than 1.5 arc minutes, and about twice that on the CEM40EC. I can guide my 2000-mm FL SCT with 0.25-0.35 arc-second rms errors. In my experience, iPolar is extremely reliable and a big time saver.

 

--Michael


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#19 Hobby Astronomer

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Posted 10 December 2020 - 09:49 PM

I love this analysis. Great job Mr. Kennedy. Stuff should perform right away. Based on your observations under a double blind testing scenario your evidence is convincing.



#20 barrabclaw

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Posted 10 December 2020 - 10:53 PM

@barrabclaw, ok, I think i'm convinced.  The center calculation will always be a center of rotation, so as long as the iPolar remains at whatever cant it is calibrated at, it should still polar align.

 

It would be interesting to know why it wasn't working for the OP.  What could iOptron have done incorrectly in that one?   

 

I looked at my guiding assistant runs from last night, and did two separate GA runs (was testing backlash really), east and west of meridian, one said 1.6' off, one 3' off.  That's consistent with every attempt; I can't imagine how to get a full degree off.  Something was clearly broken on the OP's.

Agreed. Not sure what it is but I'm pretty sure it has to do with the calibration and setting the center position. It would be really easy to tell if that's the case by seeing what the error is at two positions in RA, 90 degrees apart.



#21 msvtrove

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Posted 11 December 2020 - 12:04 AM

Agreed. Not sure what it is but I'm pretty sure it has to do with the calibration and setting the center position. It would be really easy to tell if that's the case by seeing what the error is at two positions in RA, 90 degrees apart.

Isnt it possible to club iPolar camera with Sharpcap?
This way we eliminate the doubt on iPolar Camera being misaligned.


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#22 bobzeq25

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Posted 11 December 2020 - 12:12 PM

Some discussion above about how the iPolar camera is pointing.

 

I have a PoleMaster.

 

It really doesn't care where the camera is pointing.  It can be translated, it can be pointed off axis.  The software can cope.

 

It pulls up a screen with Polaris and surrounding stars.  You use the arrow keys to rotate circles on top of surrounding stars.  That tells the platesolving what's up.  You rotate the mount and ID one of those stars at the start and the finish.  That tells the software where the RA axis is pointed.   Remember, it doesn't care where the _camera_ is pointed, exactly.  It figures it out.  It puts a green circle on the screen with the star on it.  You rotate the mount back.  The star staying on the green circle is confirmation the software has the pointing location of the RA axis right.

 

The PoleMaster then places a target where the RA axis is pointed.   Places another target on the North Celestial Pole.  You use the mount alt-az adjustments to superimpose them.

 

It.      Just.       Works.                

 

Fast and easy.  Polar alignment is better than it has to be. 

 

Leaving the mount setup in my observatory I can skip the rotation step after doing it just once.  Takes me 30-60 seconds to tweak polar alignment for the night, the mount is just sitting on the ground, rather than on a buried pier.


Edited by bobzeq25, 11 December 2020 - 12:23 PM.

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#23 jlecomte

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Posted 12 December 2020 - 12:20 PM

fyi, "the iPolar alignment system could not maintain polar alignment" -> This sentence does not make much sense, but I think I understand what you're saying.

 

Nothing in the review says whether the author used the iPolar camera in conjunction with SharpCap to achieve polar alignment. Doing so would have confirmed whether the issue came from the iPolar hardware or the iPolar software. Note: SharpCap is most definitely able to connect to the iPolar camera, which is seen by Windows as a ... webcam, which it kind of is (albeit with a slightly bigger lens)

 

I have a CEM70 mount, and adjusting the iPolar camera within the RA shaft via the set screws is actually a feature of the system. Assuming the author did not use the iPolar camera in conjunction with SharpCap to achieve polar alignment (see my previous point), it is not entirely impossible that the iPolar camera is loose, which could most definitely explain what he's been observing. I don't own the SkyGuider Pro, but I would expect that there is a way to replace the iPolar camera, and therefore check that it is tightly installed. It is a safe assumption that at this price point, some tinkering and troubleshooting may be necessary...

 

A lot of people (myself included) are getting incredibly accurate results with the iPolar camera + iPolar software (confirmed by PHD2 drift alignment, on numerous occasions, in my case) The iPolar camera hardware is desperately simple (like I said, it is pretty much a webcam with a slightly bigger lens...) so I doubt the problem comes from there (although if the lens or the sensor is loose, that could also explain it, but I think it's unlikely) The iPolar software is not great, but it kind of does an okay job (the plate solving is desperately slow...) With this in mind, it is clear that this review is not only inconclusive, but it appears to be flawed, and I would hate that people base their purchase decision on this review alone.


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#24 barrabclaw

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Posted 12 December 2020 - 03:28 PM

fyi, "the iPolar alignment system could not maintain polar alignment" -> This sentence does not make much sense, but I think I understand what you're saying.

 

Nothing in the review says whether the author used the iPolar camera in conjunction with SharpCap to achieve polar alignment. Doing so would have confirmed whether the issue came from the iPolar hardware or the iPolar software. Note: SharpCap is most definitely able to connect to the iPolar camera, which is seen by Windows as a ... webcam, which it kind of is (albeit with a slightly bigger lens)

 

I have a CEM70 mount, and adjusting the iPolar camera within the RA shaft via the set screws is actually a feature of the system. Assuming the author did not use the iPolar camera in conjunction with SharpCap to achieve polar alignment (see my previous point), it is not entirely impossible that the iPolar camera is loose, which could most definitely explain what he's been observing. I don't own the SkyGuider Pro, but I would expect that there is a way to replace the iPolar camera, and therefore check that it is tightly installed. It is a safe assumption that at this price point, some tinkering and troubleshooting may be necessary...

 

A lot of people (myself included) are getting incredibly accurate results with the iPolar camera + iPolar software (confirmed by PHD2 drift alignment, on numerous occasions, in my case) The iPolar camera hardware is desperately simple (like I said, it is pretty much a webcam with a slightly bigger lens...) so I doubt the problem comes from there (although if the lens or the sensor is loose, that could also explain it, but I think it's unlikely) The iPolar software is not great, but it kind of does an okay job (the plate solving is desperately slow...) With this in mind, it is clear that this review is not only inconclusive, but it appears to be flawed, and I would hate that people base their purchase decision on this review alone.

Well said. Using the iPolar camera with SharpCap, as a couple people have suggested, is a great idea for isolating the issue. If I had to bet, I would bet that it works well with SharpCap and that the problem is the calibration in the iPolar software. I've had it try to take the second image immediately after I move the RA axis instead of waiting for me to finish the motion. If the axis only rotates by a few degrees, the calibration will be less accurate than a motion through 90 degrees. A calibration error will also show up by attempting polar alignment with the iPolar in the iPolar software at 0 deg and then again at 90 deg. But the iPolar scope+SharpCap will be a valuable test. Hopefully the author gets a chance to try it out! Should only take a few minutes.



#25 dcm_guitar

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Posted 14 December 2020 - 12:01 PM

I'd like to add my experience to this saga......

 

The short answer is that the iPolar software (at least for some of us) simply does not work. 

 

TLDR:  DO NOT USE iPOLAR SOFTWARE.  USE THE iPOLAR CAMERA WITH A DIFFERENT POLAR ALIGNMENT SOFTWARE (e.g. Sharpcap).

 

Before I begin I'll answer:  Yes, I have downloaded the latest iPolar software.  Yes, I have checked the firmware of all my related equipment and they are up to date.

 

Camera calibration:

 

I received a new CEM40 a few days ago.  I have been trying to get the camera to calibrate per the (incomplete and incorrect) instructions in the manual.  I have made 20+ attempts at camera location calibration.  All attempts resulted in WILDLY differing camera location results.  After each calibration attempt the software would place the red cross on my screen, but would always place it an odd location; sometimes the left edge, sometimes the right edge, sometimes the top edge, sometimes the bottom edge, sometimes in the right, bottom quarter, sometimes in the upper, left third.  Despite repeated attempts at camera location calibration, I could never get a result that provided a camera alignment location that resulted in enough screen to use for alignment purposes.  

 

I manually entered camera coordinates and then iterated different polar alignments hoping I would eventually converge at a camera location calibration value that I could rely on.  I was never able to have success.  When I manually entered calibration values I was able to get a polar alignment result.  HOWEVER, after this polar alignment result, I could never get a successful one star or two star alignment on the mount.  So, the GOTO feature would fail.  I attribute this to the incorrect camera alignment values.

 

After two days I was frustrated, but felt like I would eventually converge on a solution using manually entered calibration values.  Except........(begin the playback of ominous music)

 

iPolar Software Idiocy

The Polar software decided to get even more unstable last night.

 

I decided to do some more manual calibration, polar alignment iterations last night with an eye towards eventually converging on a calibration solution.  I entered a new set of manual camera calibration values, got the red cross on my screen in a location that gave me enough room to try a polar alignment and then began the process..........For unknown reasons the iPolar software decided it wanted to do a "Rave".  The red dot showing the position of the pole would appear and then immediately disappear and move all over the screen.  It would appear very close to the red cross for 1 second, then it would disappear.  Two seconds later it would reappear at the top edge of the screen for two seconds.  Then it would disappear again, and be replaced by the maroon arrow telling me to lower the scope.  Two seconds later the maroon arrow would shift positions and tell me to raise the scope, then it would disappear and the red dot would be back right next to the cross.  Then it would disappear and the maroon arrow would be back pointing at the top right corner for two seconds and then disappear again; only to reappear pointing at the bottom left corner.  Sigh......

 

I got rather irritated (meaning I went on a profanity laced tirade that would make the Father from "A Christmas Story" blush) and gave up for the evening.

 

Finally, a Success....

 

After calming down......  I spent $15 to upgrade to Sharpcap Pro.  I went back out to the mount and decided to polar align with Sharpcap.  I decided to use the built-in iPolar camera.

 

Using the iPolar camera and Sharpcap software I was able to get a very solid polar alignment in under 10 minutes.  I was very careful and methodical, and it could have been done in less than half the time.  The Sharpcap software was able to plate solve after two observations (one with the scope in Zero position, and one with the RA 90 degrees to the "east").  Sharpcap gave me very solid and stable correction instructions and I was able to polar align with less than 1 minute of error.

 

After polar aligning with Sharpcap I did a one star alignment with my mount.  It required a bit of an adjustment and then the GOTO feature behaved beautifully.

 

So, the iPolar camera worked fine.  I was able to get a very good polar alignment using the camera.  The iPolar software is currently useless for my mount.  It will not calibrate a camera position nor will it provide stable pole locations for an alignment.

 

If you're having camera calibration issues or alignment issues with iPolar I suggest abandoning the software.  Use the iPolar camera and a more stable software solution (e.g. Sharpcap).  If iPolar works for you, that's GREAT!!!!!  If it doesn't then RUN AWAY!!!!!!


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