Does
+
=
?
That "possibly" might end up being "likely"!
Q: How many times do you have to look at a thread before it starts to gel?
f/22 in the case of the 50mm lens used here is a smallish aperture of ~2.27mm.
Our good friend "diffraction" might be at play here. The conditions were trying enough, and at f/22 with the ISO racing...!
Peter, maybe another experiment is called for. Try photographing a white sheet of paper to fill about 3/4 of the frame.
Do two runs: one in goodish sunlight, the other closer to your conditions for this lot, doing just what you did for these.