I realized a little later that the F100 cannot be convinced to open up beyond the diameter you see there--that is, I was underexposing rather a lot when I shot the test roll. How much? Well, this one was from my D100:
And this one was from the F100 with Plus-X:
I like the second photo more than the first--it has a certain dark quality to it. But it is not what was supposed to come out of the camera, so back it goes.