The optical distortion polynomial coefficients derived from the pinhole mask is 
applied to four selected points in the FOV (e.g. pixel 262,762). 
The resulting correction shifts in pixel are applied in later steps of the 
data reduction chain is plot.   
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The black points are the optical distortion shifts of FOV positions with
250 pixel distance (in x and y, hence r=sqrt(2) *250) from the center
(512, 512), while the red points are the optical distortion shifts of FOV
positions with 500 pixel distance (in x and y, hence radial distance =
sqrt(2) * 500 pixel)  from the center (512, 512),