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Error Tryin To Polar lign

Sky-Watcher AZ-GTi Equipment Equatorial Mount Polar Alignment
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hatflyer avatar
hatflyer avatar
I am using NINA to 3-point align. Before that, I set my lat/long, and roughly PA to within a few degrees (I set the latitude on the wedge with 40 degrees, my latitude in the northern hemisphere). When I then 3-point align, the azimuth error is minimal. But the altitude error is 90 degrees.

I have a DSLR and the AZ-GTi mount in EQ mode. When I align, the mount rotates only around the RA axis.

Any ideas? Here's my set-up:


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andrea tasselli avatar
andrea tasselli avatar
IS the RA axis pointing northward?
kuechlew avatar
kuechlew avatar
This erratic error in NINA can happen when your initial setup has a large polar alignment error of several degrees. I ran into this issue too. I also managed to create a situation where NINA told me to move the mount to the left while in reality I had to move it to the right. Try to perform an initial rough polar alignment  with a compass, an app like Polar Scope Align Pro. Actually just finding Polaris in the sky and pointing you mount towards Polaris judging by eye should be accurate enough.

Good luck and clear skies
Wolfgang
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hatflyer avatar
hatflyer avatar
I did have the mount within a few degrees to start with.

But I think I have the issue. I used an L-bracket attaching my camera to my dove tail plate. So the camera axis is 90 degrees from the plate, which happens to be the error amount, 90. I will remove the L-bracket, line up the camera, and hope that's it.


Thanks.
kuechlew avatar
kuechlew avatar
Please report back if this solved the issue. In theory the orientation of the camera should not play a role as long as you don't change it during the process of polar alignment. The software should just evaluate the change of the plate solved field by the rotation along the RA axis in order to calculate the axis of rotation of your setup and compare it to the expected position of the earth's axis of rotation.

Clear skies
Wolfgang
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hatflyer avatar
hatflyer avatar
kuechlewPlease report back if this solved the issue. In theory the orientation of the camera should not play a role as long as you don't change it during the process of polar alignment. The software should just evaluate the change of the plate solved field by the rotation along the RA axis in order to calculate the axis of rotation of your setup and compare it to the expected position of the earth's axis of rotation.

Clear skies
Wolfgang

Unfortunately u are correct. No change. I still can't get TPPA to work. I checked location is set properly (see photos for Synscan and NINA), the RA axis rotates when doing 3-point. I tried removing an L-bracket to make the camera in-line with the release plate (made no difference). Why is NINA unable to recognize my EQ mount is tilted up 40 degrees, as set on the wedge? Azimuth works fine. This can't be so complicated.
Lars Bartels avatar
Lars Bartels avatar
Weird…Well, I take photos from several locations and have never changed the information under "Astrometry" in N.I.N.A. so far. I have entered the location of my garden there once, but I have never changed it. Even if I photograph from the garden of my girlfriend, which is 40km further away from my garden, this setting has not had any effect on whether the Three Point Polar Alignment works or not. I always use the "start from current position" setting in TPPA.

Can you show us your settings from the TPPA?
kuechlew avatar
kuechlew avatar
As I already said I ran into the same issue on occasion. In my case it helped to try to improve the starting position of the polar alignment. I actually had a similar experience with the iOptron iPolar which doesn't seem to work reliably if you're too much off the mark. You could try to perform the polar alignment with different declination orientations of your camera. Not sure if this helps. 

I don't believe that this causes the issue but just to be sure: When I was still using a camera and a lens I realised that there can be a slight "wobble" between the lens and the camera mount for some lenses. This could screw up the alignment process. I don't know either how well the NINA process works with wide fov. You seem to be using an 85mm lens. With such a wide field approach you don't have to be too picky about polar alignment and a rough polar alignment may be good enough.

Clear skies
Wolfgang
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