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I have a code block that calculates the ellipticity components e1 and e2 given the approximate coordinates of a star. I calculate ellipticity and its components e1 and e2 (stretching along x/y and y=x/y=-x). Once I calculate the components, the ellipse's major axis is at an angle a = 1/2 arctan(e2/e1) from the positive x-axis, so then I can calculate what the rotation of the focal plane was for this image, and from that back out this angle in that reference frame.
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Just realized that although the running mean I calculated in the real notebook yesterday was correct and in the rotated frame, my plots above are NOT in the rotated plane and should be re-made. New plots (for four of the pairs):
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