Welcome, Guest
Username: Password: Remember me
14 Nov 2018
Glad to announce of release of INDI Library v1.7.5 on 2018-11-14. A few drivers were added in this release as we continue to improve & stabilize existing drivers.
Read More...
  • Page:
  • 1
  • 2

TOPIC: Polar alignment module and CEM60 geometry

Polar alignment module and CEM60 geometry 4 months 1 week ago #27185

  • fmozza
  • fmozza's Avatar Topic Author
  • Away
  • Senior Boarder
  • Senior Boarder
  • Posts: 47
  • Thank you received: 7
Thanks for your comments, and no need to apologize for trying to help a fellow imager. I've been imaging for about 7 years, give or take, but the CEM60 is new to me, as is KSTARS/INDI/EKOS, so there is a learning curve. Using my Polar scope, I can get to about 5 to 8 arcmin of NCP, and will work reasonably well at my current focal length of 900mm, but I want a crack at imaging with my C11 @ 2800mm with exposures on the order of 10min or so. I know I'll have problems with mirror shift, but if I can get really close to NCP, that will help to limit rotation I see at long focal lengths.

It might be helpful for folks to know I am not using a tripod - my mount is on concrete pier sunk about 15 feet down, so its stable. (There's a story behind this, but where I live, the frost depth can hit 8ft, so you need to have sufficient depth to counteract frost heaves.)

I'm really happy with the CEM60 adjustments for Alt/Az - not as good as a really high-end mount I suppose, but it's a big step compared to my old CGEM. I am scratching my head with the Polar alignment module - when I set the vector tip on a star, I'm able to move the star to the crosshairs and hit the middle ease, but when I repeat the exercise to check my alignment, the result is far worse than when I started.

Stay tuned - I'll have another crack at this in another hour, provided the clouds stay away...

jmh

Please Log in or Create an account to join the conversation.

Polar alignment module and CEM60 geometry 4 months 1 week ago #27186

  • fmozza
  • fmozza's Avatar Topic Author
  • Away
  • Senior Boarder
  • Senior Boarder
  • Posts: 47
  • Thank you received: 7
There was intermittent clouds tonight, but I decided to follow the process as per the instructions, collect the logs, and do screen captures so you can all see what I've done.

Here are the align module logs:

[2018-07-05T22:57:53.294 CDT DEBG ][ org.kde.kstars.ekos.align] - P1 RA: "02h 31m 33s" DE: " 89° 15' 50\""
[2018-07-05T22:57:53.294 CDT DEBG ][ org.kde.kstars.ekos.align] - P2 RA: "00h 38m 24s" DE: " 89° 13' 55\""
[2018-07-05T22:57:53.294 CDT DEBG ][ org.kde.kstars.ekos.align] - P3 RA: "22h 48m 24s" DE: " 89° 13' 14\""
[2018-07-05T22:57:53.294 CDT DEBG ][ org.kde.kstars.ekos.align] - P1 X: 119.525 Y: -48.4096
[2018-07-05T22:57:53.295 CDT DEBG ][ org.kde.kstars.ekos.align] - P2 X: 412.35 Y: 405.71
[2018-07-05T22:57:53.295 CDT DEBG ][ org.kde.kstars.ekos.align] - P3 X: 896 Y: 643.5
[2018-07-05T22:57:53.348 CDT DEBG ][ org.kde.kstars.ekos.align] - RA Axis Circle X: 1083.44 Y: -348.489 Radius: 1009.54
[2018-07-05T22:57:53.348 CDT DEBG ][ org.kde.kstars.ekos.align] - RA Axis Location RA: "22h 48m 49s" DE: " 89° 54' 35\""
[2018-07-05T22:57:53.348 CDT DEBG ][ org.kde.kstars.ekos.align] - RA Axis Offset: " 0° 05' 24\""



[2018-07-05T23:21:39.264 CDT DEBG ][ org.kde.kstars.ekos.align] - P1 RA: "02h 32m 11s" DE: " 89° 15' 44\""
[2018-07-05T23:21:39.264 CDT DEBG ][ org.kde.kstars.ekos.align] - P2 RA: "00h 52m 35s" DE: " 89° 12' 32\""
[2018-07-05T23:21:39.264 CDT DEBG ][ org.kde.kstars.ekos.align] - P3 RA: "23h 16m 30s" DE: " 89° 11' 42\""
[2018-07-05T23:21:39.264 CDT DEBG ][ org.kde.kstars.ekos.align] - P1 X: 181.254 Y: 33.2729
[2018-07-05T23:21:39.264 CDT DEBG ][ org.kde.kstars.ekos.align] - P2 X: 454.614 Y: 438.198
[2018-07-05T23:21:39.264 CDT DEBG ][ org.kde.kstars.ekos.align] - P3 X: 896 Y: 643.5
[2018-07-05T23:21:39.322 CDT DEBG ][ org.kde.kstars.ekos.align] - RA Axis Circle X: 1045.77 Y: -255.614 Radius: 911.502
[2018-07-05T23:21:39.322 CDT DEBG ][ org.kde.kstars.ekos.align] - RA Axis Location RA: "23h 31m 25s" DE: " 89° 49' 00\""
[2018-07-05T23:21:39.322 CDT DEBG ][ org.kde.kstars.ekos.align] - RA Axis Offset: " 0° 10' 59\""

And these indeed show that the alignment is worse. The attached zip contains the images that shows what I did. There was a couple of Capture and Slew to target steps that I didn't bother to capture - I wanted to start the second attempt from as close to the same position as the first attempt.

The cloud rolled in again, so I couldn't do the reverse process. The forecast is clear for tomorrow night, so I'll do that tomorrow night. But in the meantime, have a look and let me know if I'm doing the right things.

jmh
Attachments:

Please Log in or Create an account to join the conversation.

Last Edit: by fmozza.

Polar alignment module and CEM60 geometry 4 months 1 week ago #27188

Interesting... the fact that the RA offset afterwards is almost exactly twice the original value, and almost exactly the same angle, does seem to strongly suggest that the correction guide is telling you to go the wrong way. I can't see how this could possibly have anything to do with your mount, but at the same time, it seems strange that no one else would have encountered this and brought it up already. I've had fairly inconsistent results with trying to do polar alignment corrections myself, but I never seem to get to the point where the star is perfectly centered in the crosshair, mainly due to camera/plate solving issues that show up during the "refresh" phase. Anyway, I think that what you're seeing here certainly merits a closer look, since your results are quite telling and I don't see any reason why you'd be experiencing this and others wouldn't.

Judging by the screenshots you posted, it appears that the correction vector is correct relative to the calculated center of rotation... the dashed green circle appears to be centered below and to the left of the NCP on the yellow grid, which would suggest that the mount needs to be raised and aimed to the right slightly. This would cause the star to move down and to the left in the image, which is what the correction guide is telling you to do. The question, then, is what is wrong? Is the center of rotation calculation incorrect, causing both the green circle and the correction guide to be mirrored 180 degrees? Very strange...

Please Log in or Create an account to join the conversation.

Last Edit: by smhxx.

Polar alignment module and CEM60 geometry 4 months 1 week ago #27190

What version of KStars are you running? Are you on 2.9.6 or are you running a nightly/bleeding-edge build? If the version you are using was built after June 3, perhaps it's possible that these changes are responsible? It seems likely to me that this is a regression of some sort, as I seriously doubt that the Polar Alignment Helper could have been broken ever since it was introduced a year ago and nobody would have noticed. It does look like some fairly major changes were made, so perhaps the bug was introduced there? These changes were made after 2.9.6 (the latest stable version) was released though, so unless you're running the bleeding-edge version, the problem would have to be older than that.

Please Log in or Create an account to join the conversation.

Polar alignment module and CEM60 geometry 4 months 1 week ago #27216

  • fmozza
  • fmozza's Avatar Topic Author
  • Away
  • Senior Boarder
  • Senior Boarder
  • Posts: 47
  • Thank you received: 7
I'm running 2.9.6 bleeding, specifically

kstars-bleeding/xenial,now 6:2.9.6+201805251429~ubuntu16.04.1 amd64 [installed]

Please Log in or Create an account to join the conversation.

Polar alignment module and CEM60 geometry 4 months 1 week ago #27222

The recent changes just changed the workflow, not the calculations. It does look like the correct vector is mirrored. The code defines the correction vector as follows:
correctionVector.setP1(celestialPolePoint);
correctionVector.setP2(RACenterPoint);

Now I noticed that I wasn't calculating the Position Angle between the Mount Axis Center & Celestial Pole, it was just measuring the magnitude between them. Could it be that the PA would determine the orientation of the correction vector? Maybe most folks had PAs that wouldn't warrant a "flip" but you did? Of course this is all in the air and speculation, so I added more debug statements.

Tonight, I will test it in my observatory. First I will do a normal check, then I will try to adjust the mount to reflect your misalignment and see how it goes.
The following user(s) said Thank You: Herrhausen, fmozza, smhxx

Please Log in or Create an account to join the conversation.

Jasem Mutlaq
Support INDI & Ekos; Get StellarMate Astrophotography Gadget.
How to Submit Logs when you have problems?
Add your observatory info
Last Edit: by knro.

Polar alignment module and CEM60 geometry 4 months 1 week ago #27232

  • fmozza
  • fmozza's Avatar Topic Author
  • Away
  • Senior Boarder
  • Senior Boarder
  • Posts: 47
  • Thank you received: 7
Thanks for your efforts on this. I did the reverse movement using the vector provided and I think I have success at 22arcsecs off NCP - take a look at the attached screen capture. But, I no longer see Polaris in my polar scope, so either it is way out, or something else is going on. As I type this, I am running the Guiding Assistant in PHD2 - I'll get it run for 20min or so and see what it computes as the Polar Align error - it probably will be a bit more as I'm doing this in a wind between 25 and 35 kph. At least its dark...

I picked a star close to the intersection the meridian and the equator and ran the PHD2 guiding assistant for about 1000 seconds - it reported a polar alignment error of 6.4 minutes. Given it was windy and PHD2 had an issue with the calibration, I don't know how accurate the estimate was. It also reported a DEC drift rate of about -1.67" per minute - that would indicate more that a 22" polar align error I think.
Attachments:

Please Log in or Create an account to join the conversation.

Last Edit: by fmozza.

Polar alignment module and CEM60 geometry 4 months 1 week ago #27318

fmozza,

I had recent problems with polar alignment, because I am using a diagonal
in front of the camera, which mirrors (horizontally flips) the image.

Are you using an imaging train that has an odd number of reflections?
That would cause a mirror image. I may be off here, but I did not get
a response to my initial entreaties, and my experiments led me to
use the capability of my camera driver to "flip" the image horizontally.

This *seems* to have fixed the problem for me, but your camera may
not have that capability, and I *still* may be incorrect, not having received
input from the developers. Yet, my "fix" seems to work.

See my previous posts on this subject, and weigh in if you like.

Gregory

Please Log in or Create an account to join the conversation.

Polar alignment module and CEM60 geometry 4 months 1 week ago #27320

I may be wrong, but if I understand the math being used to determine the alignment of the RA axis, it seems that the images being mirrored should not affect the result... or at least, if it does affect the output somehow, I'd consider that a bug. Astrometry.net is capable of handling images of either positive or negative parity (i.e. "normal" vs. "flipped,") so unless the Astrometry.net settings are incorrect, such as being told to only search for positive-parity solutions when the images actually have negative parity, they should still solve. Each of the three solved plates equates to a great circle on the celestial sphere, defined by the central coordinate of the image and its rotation, neither of which should be affected by the parity of the images, and these three great circles should intersect (or roughly intersect, accounting for error) at two points corresponding to +90 and -90 degrees declination. That's not to say that mirrored images definitively aren't to blame, simply that there's no practical reason why the system wouldn't be able to handle them, as far as I can tell.

Please Log in or Create an account to join the conversation.

Polar alignment module and CEM60 geometry 4 months 1 week ago #27337

  • fmozza
  • fmozza's Avatar Topic Author
  • Away
  • Senior Boarder
  • Senior Boarder
  • Posts: 47
  • Thank you received: 7
Greg,

Thanks for chiming in. I read through your posts and am a little more puzzled. I have no diagonals in my setup. The image parity is negative, but parity or orientation shouldn't matter. One possibility is that the software makes an assumption of what hemisphere I'm in - I'm north, but if the software assumes south, then the difference in vector direction makes sense.

jmh

Please Log in or Create an account to join the conversation.

Polar alignment module and CEM60 geometry 4 months 1 week ago #27345

Actually, I got an email before from a user in the southern hemisphere saying the correction vector was opposite, so I disabled any modifications for south hemisphere. Maybe I just got them switched? Need to look again.

Edit: never mind, the email was about rotation direction of mount in the rotation phase and not about correction vector.

Please Log in or Create an account to join the conversation.

Jasem Mutlaq
Support INDI & Ekos; Get StellarMate Astrophotography Gadget.
How to Submit Logs when you have problems?
Add your observatory info
Last Edit: by knro.

Polar alignment module and CEM60 geometry 4 months 3 days ago #27442

jmh recently wrote:

> I read through [Greg's] posts and am a little more puzzled. I have no diagonals in my setup.

I see...then, no reflections, or an even number of reflections?

> The image parity is negative, but parity or orientation shouldn't matter.

I quite agree. And to re-state, there is no problem I can see with solving or
astrometry.net, which seems to be able to solve no matter the parity or
orientation; and the calculated *positions* are correct.

What I question (only from experiment, not from knowledge of the code),
is the calculation of the correction vector.

> One possibility is that the software makes an assumption of what hemisphere I'm in -
> I'm north, but if the software assumes south, then the difference in vector direction
> makes sense.

I hope a developer can determine what's going on, *if* anything is going on. :-)
My *guess* would be that the calculation of the correction vector *may* be off
under certain circumstances. (?)

Greg

Please Log in or Create an account to join the conversation.

  • Page:
  • 1
  • 2
Time to create page: 0.188 seconds

Login



3rd Party

Choose from the numerous 3rd party INDI drivers to suit your needs!

Got Problem?

Check out the FAQ, the forum, and the bug tracking system to resolve any issues you might have!
You can also subscribe to INDI newsletter and development mailing lists to get the latest updates on INDI!


Gallery

Replica

Why INDI

Replica