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themos

Looking for beta testers of new Polar Alignment utility.

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Hello,

if you would like to volunteer to try out a new Polar Alignment method, please let me know. The requirements are:

  • You can see the Polaris/NCP region from where you usually set up. (South hemisphere? get in touch!)
  • You can attach a camera to the mount and bring the JPEG image files to your computer.
  • You can freely rotate the RA axis (this excludes AstroTrac mounts and similar, I think).
  • You have Internet connectivity.
  • You can run Python on your computer (e.g. Anaconda for Windows, Linux, MacOS X)

You might be able to verify your Polar Alignment within 2-3 minutes. The software will be in the public domain.

Regards

Themos Tsikas

PS: (added in edit, latest version for Windows, 1.0.4 https://drive.google.com/open?id=0Bws-dmFqKZThUjBtc2FCeENOdXc )

Edited by themos
latest version
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Count me in :) more than willing to give it a go :)

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Sounds good.  Unfortunately at the moment it looks as though I will be unable to help for a while.  Unless it's possible to polar align without being able to see any stars whatsoever.  For weeks :(

James

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Sounds interesting! I've been researching how to polar align using 2 plate solved images and then making the adjustment by re-centring an off-set star. Trying to get my head around the maths part but got the plate solving part sorted.

http://webpages.charter.net/dware1/Projects/Polar_Alignment_Equation.pdf

Hi Russell

Astrotortilla combined with a little utility called polefocus (http://www.scopefocus.info/polar-alignment) does that! :)

Louise

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Hi Russell

Astrotortilla combined with a little utility called polefocus (http://www.scopefocus.info/polar-alignment) does that! :)

Louise

Thanks Louise. But the AT method requires clear sight of the east or west horizons, which I don't have from my observing location. I want to be able to polar align with any pair of points I choose.

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Will this be better than the polar align tool in eqmod?

Sent from my Vodafone Smart 4 turbo

At least as accurate but faster would be my measure of better :)

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Thanks Louise. But the AT method requires clear sight of the east or west horizons, which I don't have from my observing location. I want to be able to polar align with any pair of points I choose.

Hiya

Yeah - strictly... There's obviously reasons why trying to measure PA error can't be done too far from optimal positions. However, AT does seem to have a certain tolerance. As you know the East or West is just for alt adjustment. Fortunately I can see due East or West but I would imagine +/- 15deg would still be fine, maybe even further from due E/W would still be possible. Having said that, I'm not certain how near to the horizon you have to be to get an accurate alt error. The link below suggests measuring at about 20 deg of altitude (not too low because of atmospherics). People seem to recommend between 20 and 30 deg.

There's some drift aligning theory here: http://www.shadycrypt.com/pages/Collins_derivation/Derivation.htm

(From my flat) I can't see South for az adjustment. I can only see at either about 150 deg (East side) or about 240 deg (West side). Still seems to work ok for adjusting az (at least for imaging with shortish focal lengths :) ).

As I understand it, if you can achieve negligible az error then you can still correct for alt error at some distance from the optimal E/W measurement position. I try and make sure my az error is at least minimised before measuring/adjusting alt anyway ( http://celestialwonders.com/articles/polaralignment/MeasuringAlignmentError.pdf ).

I did come across a site that reckons you can PA on a single star - http://celestialwonders.com/articles/polaralignment/StarOffsetPositioning.pdf

Louise

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Thank you, Earl, Steve_Max127 and RusselHQ!

A couple of points :

  • polefocus requires ASCOM mount, PhotoPolarAlign won't. You can use a barn-door mount or a Dob equatorial platform. polefocus requires the measured Az/Alt polar alignment error which PhotoPolarAlign can provide. AstroTortilla can also provide that error but the last version I used produced unreliable and wildly fluctuating estimates.
  • The EQMOD polar align tool that simulates the polarscope view has been my preferred method. However, it's tied to the EQMOD supported mounts and your alignment is only as good as your reticle calibration.
  • I found AlignMaster to be almost useless for my location as most of the stars it wanted to slew to were behind trees. It also requires GoTo capability. 

I will be in touch with the beta testers soon.

Clear skies!

Themos

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Looks very interesting

My Meade LX F6.3 + Canon 1000D gives 1.1 arcsec/pixel.

I see your taster is working at 21.98.

What sort of range does PPA work over?


Michael 

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Michael, I have used it with around 5 arcsec/pixel. The images above were reduced by a factor of 4 from the originals. You probably don't want to take the images with the Canon set to the highest resolution. You would use the 1936 x 1288 pixels resolution. PPA will upload the images to nova.astrometry.net for plate-solving so you don't want very big images. If your typical 15 second exposure is recognised by nova.astrometry.net you will have no trouble with PPA. 

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does this require the pount to be at a measured posistion to base the posistion from?

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does this require the pount to be at a measured posistion to base the posistion from?

No, it doesn't. I will be writing the Help file next so once that is done you can have a play. 

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Daft question, but does this align the optical axis or the mount axis with the NCP?

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The mount (or RA or polar) axis! 

After a rough polar alignment, I set the camera somewhere close to declination 90 so I can see Polaris in the field of view. Keeping the camera fixed to the mount, I slew in RA by a large angle (40 degrees say) and watch where Polaris goes. If it goes off the FOV, the RA axis is not close to Polaris. So I adjust the polar alignment, bring Polaris back into the FOV and try again (the details of this iteration need to be worked out). Once it's set so that Polaris stays in FOV after a large RA slew, we are good to fine-tune the polar alignment by PhotoPolarAlign. The first two images give us the position, in pixel coordinates, of the RA axis (the red cross). I take the first image at an RA position so that the sensor is taking a picture of the sky in "portrait mode" and the second image in "landscape mode", with the long side of the sensor horizontal. The plate solving tells me where the NCP is (allowing for precession  since 2000), in pixel coordinates and what the scale is. Now that the camera is horizontal, x and y pixel offsets translate directly into instructions to move the mount RA axis up-down or right-left by so many arcminutes.  After I adjust the polar alignment, I take another image and check for improvement. The RA axis pixel coordinates have not changed, only the NCP pixel coordinates move. With practice, it should take only 3-4 iterations to get it close enough (whatever close enough is for your imaging needs).

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if you can send some clear skies I'd like to have a go as I need to polar align my mount to the garden pier again. I'll be the idiot user  - if I understand it then most will.

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If there is room for any more I'd like to have a go. Tried the AT method and got nowhere.

The thought of spending another night fighting with PA is putting me right off.

Ta

C. 

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Themos,

I use AstroArtV5 which has built-in plate solving....could this be used with your proposed method?

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I've added you, cthorpey. I will work on the help document over the weekend, hopefully. 

Merlin66, does it produce .wcs files for each image solved? I might make a more self-contained version that requires you to input the pixel coordinates of Polaris and Lambda UrsaMinoris, although nobody likes to type numbers in the dark. 

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