One more try - the central shadow is centered in the
bright rings, and they are centered within the inner
edge of the dim outer ring. I gave up trying to keep
this outer ring even. Moving the surface on which the
pattern is projected closer to the scope brought the
outer ring closer to the inner set, making it easer to
judge the centering. The 4 secondary vanes also seem to
intersect the bright inner rings evenly now, unlike the
previous attempt. See the next image for the
results.