I have in my head an idea for a simple tool to characterise blur. All it requires is to the take the astigmatism “sunrise” tool (the one with all the spokes radiating out) and put in small calibrated gaps. (Could also think of it as straightening out some Landolt C’s and using them to construct the sunrise.)
The idea is that blur causes the gaps to be filled in. Isotropic (myopic) blur should fill in all the gaps uniformly. Anisotropic (directional / astigmatic) blur would fill in the gaps only in on the lines which lie parallel direction of the blur.
(I actually conceived it to try to prevent ghost images from masking blur - same sort of principle - the ghosting happens in one direction, and so you can look for the blur happening on the line that’s perpendicular to that.)
Does this make any sense ?