Don, yes the masking idea would work fine IF I was looking at only one or two at a time. BUT this is an aerial roll of 324 9"x 9" negs with what is colled a solar flare that moves slowly from the NE corner to the NW corner as the day of flying progressed. It is considered quite normal for this type of stuff. Most shops would leave that corner off colorwise and in densitywise. I am trying to get them both to settle.
Thilo, no I don't believe I have a closed loop system. It is just a really BIG horizontal camera/track/copyboard system. All open except the lightdeck itself. And actually I can pinregister lith film or ortho film which is the usual correction if density is the only issue. Surprising, when I used under developed lith film for a softer mask, it did change the color, but the wrong way, so the lith film's black must have a color registration on my camera. It was slight, but it is there. I have even used layers of frosted polycarbon, again does fine for density but it seems to hold back the yellow dye formation which would imply that it has a yellow cast. BTW the softer lith film held back the same color.
This evening when it cools down around here, I have to do this one way or another. As I was drifting off to sleep last night I thought of a potential solution. Maybe if in the strongly printing area I use one extra polycarbon layer and one .10 lavendar, instead of two of the pc, maybe. . . anyway I will let you know if it works.