Polar alignment and field distortion
Posted: 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?
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?