gainer said:
Your halo may be lens flare. Have you photographed the same scene before?
I haven't done that scene before, but I had a similar thing occur again on a different pyrocat roll this morning that might help to figure it out.
In my past experiences (xtol, d-76), if you had, for example, the sun at the edge of a frame, the exposure would bleed outside of the frame and in the frame because of both scattered light in the emulsion and infectious development. That bleeding would be the same density as the sun and then taper off gradually. It's a blasting glow and you lose details of the light source and things near it.
The strange thing I am seeing is that in grossly overexposed skies, I get something that reminds me of this "sun at the edge of the frame" thing where I'm getting a uniform bleed (no star patterns from the aperture or circles from flare) outside and inside the frame, but it is much lighter--my edges are precise and I'm not losing details of the light source, but I get a mildly dense glow around grossly overexposed areas.
My guess is that this is scattered light in the emulsion and it looks different because of pyrocat's surface development and minimal infectious development.
If I put my scanner back together this week (I took it apart a year ago and tried to make a large format d*g*tal camera out of it), I'll post some examples.