Polar alignment and field distortion

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Joined: Wed Oct 17, 2018 6:24 am

Polar alignment and field distortion

Post by mxpwr » Wed Oct 17, 2018 7:01 am

I have been using polar alignment with sharpcap for a while now.
I use a 50mm F1.8 lens with a 5mp sony IMX326, FOV is around 4degrees and the whole procedure runs usually very smooth.
While it seems to get PA pretty close (below 1minute on both axis), I noticed some strange things with sharpcap's PA and was wondering if errors might come from field distortion in the lens used.

After rotating by 90degrees, i align both axis and then I do a sanity check by rotating forth and back 180. What I see is that often the calculated PA error jumps (by 1 to 2 minutes) when a different star is picked or when the star has moved enough in the image.
Since everything is rock solid on the setup, I would assume that flexing is not the main suspect here, but maybe field distortion.

Would it make sense to add support for distortion polynomials to try to reduce this effect?

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