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08 Apr 2018
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TOPIC: Polar alignment module and CEM60 geometry

Polar alignment module and CEM60 geometry 2 weeks 1 hour ago #27100

  • fmozza
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I am attempting to polar align my CEM60 using the polar alignment module. After the first attempt, I was 30 arcmin off, and after the second attemp, 34 arcmin off.

Is there something about the CEM60 geometry that doesn't work with the polar module?

Any and all pointers appreciated!

jmh

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Polar alignment module and CEM60 geometry 1 week 6 days ago #27110

Try to enable logging in Ekos (Click button called Logs in Ekos main screen). Then check INDI & Mount & Align and make sure it is set to "Verbose", then perform your Polar Alignment and attach the log file.

But to answer your question, there shouldn't be any "geometry" issues as long it's an equatorial mount and everything is rigid and set in place. What was your FOV?

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Jasem Mutlaq
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Polar alignment module and CEM60 geometry 1 week 6 days ago #27122

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Thanks for your response. Everything was rigid and tightened down.

I've attached the log file. Interesting bits start about 22:30.

FOV was about 72 x 51 arcmin.

jmh
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Polar alignment module and CEM60 geometry 1 week 6 days ago #27126

The log doesn't contain the "Align" information. Make sure "Align" in checked in Logs.

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Jasem Mutlaq
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Polar alignment module and CEM60 geometry 1 week 6 days ago #27139

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See attached log file.

Thanks,

jmh
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Polar alignment module and CEM60 geometry 1 week 5 days ago #27147

First time
[2018-07-04T22:30:37.772 CDT DEBG ][     org.kde.kstars.ekos.align] - P1 RA:  "21h 29m 25s" DE:  " 89° 27' 36\""
[2018-07-04T22:30:37.772 CDT DEBG ][     org.kde.kstars.ekos.align] - P2 RA:  "21h 09m 42s" DE:  " 89° 20' 27\""
[2018-07-04T22:30:37.772 CDT DEBG ][     org.kde.kstars.ekos.align] - P3 RA:  "20h 38m 12s" DE:  " 89° 15' 26\""
[2018-07-04T22:30:37.773 CDT DEBG ][     org.kde.kstars.ekos.align] - P1 X:  911.466 Y:  281.908
[2018-07-04T22:30:37.773 CDT DEBG ][     org.kde.kstars.ekos.align] - P2 X:  851.831 Y:  462.153
[2018-07-04T22:30:37.773 CDT DEBG ][     org.kde.kstars.ekos.align] - P3 X:  896 Y:  643.5
[2018-07-04T22:30:37.823 CDT DEBG ][     org.kde.kstars.ekos.align] - RA Axis Circle X:  1193.12  Y:  475.082  Radius:  341.532
[2018-07-04T22:30:37.823 CDT DEBG ][     org.kde.kstars.ekos.align] - RA Axis Location RA:  "19h 50m 44s" DE:  " 89° 26' 57\""
[2018-07-04T22:30:37.823 CDT DEBG ][     org.kde.kstars.ekos.align] - RA Axis Offset:  " 0° 33' 02\""

Second time:
[2018-07-04T22:49:56.817 CDT DEBG ][     org.kde.kstars.ekos.align] - P1 RA:  "23h 05m 45s" DE:  " 88° 57' 58\""
[2018-07-04T22:49:56.817 CDT DEBG ][     org.kde.kstars.ekos.align] - P2 RA:  "22h 45m 51s" DE:  " 88° 52' 53\""
[2018-07-04T22:49:56.817 CDT DEBG ][     org.kde.kstars.ekos.align] - P3 RA:  "22h 21m 45s" DE:  " 88° 51' 02\""
[2018-07-04T22:49:56.817 CDT DEBG ][     org.kde.kstars.ekos.align] - P1 X:  669.179 Y:  377.245
[2018-07-04T22:49:56.817 CDT DEBG ][     org.kde.kstars.ekos.align] - P2 X:  744.391 Y:  545.77
[2018-07-04T22:49:56.817 CDT DEBG ][     org.kde.kstars.ekos.align] - P3 X:  896 Y:  643.5
[2018-07-04T22:49:56.896 CDT DEBG ][     org.kde.kstars.ekos.align] - RA Axis Circle X:  986.474  Y:  336.685  Radius:  319.876
[2018-07-04T22:49:56.897 CDT DEBG ][     org.kde.kstars.ekos.align] - RA Axis Location RA:  "22h 20m 38s" DE:  " 89° 04' 08\""
[2018-07-04T22:49:56.897 CDT DEBG ][     org.kde.kstars.ekos.align] - RA Axis Offset:  " 0° 55' 51\""

So it appears the calculations are correct. What was the correction vector you got for the first go? I presume you centered the star by adjusting Alt & Az knobs on the mount?

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Polar alignment module and CEM60 geometry 1 week 5 days ago #27159

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I should have taken screen shots of the Alignment windows as i went - I'll try that tonight as I think it will illustrate what I think might be happening, And I do use the Alt/Az knobs, not the controller. (I know you have to ask ... ;-))

My first attempt resulted in a polar alignment error of 33arcmin. When I made the correction, and start the second attempt, the reported error was about 55arcmin. I never bothered trying to move the move on the second try and went back to using the polar scope that comes with the CEM60. My polar scope is slightly misaligned, but the interesting thing is that all of the mount movements required to get Polaris where it needed to be on my polar scope were exactly the opposite of what the Polar alignment module wanted me to do.

After I used the Polar scope, I went back to the alignment module, and it reported the Polar alignment error to be 5arcmin. This is where I should have taken a screenshot, because I could clearly see NCP, the circle of rotation for the current mount position, and the vector - the direction of the vector was suggesting I move the circle of rotation away from the NCP position, not towards it. Could it be that the direction is flipped somehow? Anyway, the clouds moved in, so I couldn't test it. I'll try again tonight and take screenshots as I go through the process.
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Last Edit: by fmozza.

Polar alignment module and CEM60 geometry 1 week 5 days ago #27160

It's a possibility... looking forward to the screenshots + logs again.

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Jasem Mutlaq
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Polar alignment module and CEM60 geometry 1 week 5 days ago #27161

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As a test for this hypothesis instead of clicking on a star so the pink direction line starts there, click away from it so the line ends there and then make sure that the star ends up at the start of that line. If you are right then polar alignment should be perfect.

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Modded Canon EOS 700D with a WO ZS 71 ED on a SW HEQ5-Pro /
QHY9 CCD and filter wheel with an 8" RC on a SW AZ-EQ6

Polar alignment module and CEM60 geometry 1 week 5 days ago #27174

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Exactly what I was planning.

jmh

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Polar alignment module and CEM60 geometry 1 week 5 days ago #27175

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Great minds think alike :whistle:

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Modded Canon EOS 700D with a WO ZS 71 ED on a SW HEQ5-Pro /
QHY9 CCD and filter wheel with an 8" RC on a SW AZ-EQ6

Polar alignment module and CEM60 geometry 1 week 5 days ago #27183

Keep in mind (if this isn't obvious to you already, in which case I apologize) that the adjustments you make to your mount, and the resulting motion of the star within the image will be diametrically opposite. To use a hypothetical example, say that you use the polar alignment utility, and it tells you that the NCP is 30 arcminutes up and to the left of your current center of rotation. That is, you need to adjust your mount's polar alt/az knobs to bring your RA axis upward and leftward by 30 arcminutes. When you do this, the camera moves up and to the left, so the star (which is stationary) will appear to move down and to the right within the frame. Once you've finished correcting for the polar alignment error, the star will be 30 arcminutes down and to the right of its original position in the image, the opposite direction of the adjustment you made.

Another observation that I can offer, as someone who likewise has struggled with getting accurate polar alignment, is that the adjustments you will need to make to the mount's alt/az knobs are very small. For reference, if you own a Telrad, 30 arcminutes is the angular diameter of the smallest circle at the center of the reticle. You may end up only turning the knob 1/16 of a turn, or something of that magnitude. It may be more than that depending on the thread pitch of your mount's adjustment knobs, but the point is that it's best to take small steps and check your progress regularly. I usually try to take it slow, check the refresh images, and make the smallest possible adjustments that I'm physically capable of making until eventually I get there.
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