Originally Posted by Greg Davis
Other possible causes of fogging are:
Flare from internal reflections from a too-large image circle. This can be especially troublesome when there is a lot of bright areas just outside of the framed image. When using a compendium, extend it till it impinges on the ground-glass image then back off a bit for maximum effect.
Light hitting the glass surface of the lens/filter itself from an oblique angle just outside the field of view. A well-adjusted compendium should fix this too.
Do you have a coated ND filter? If not, then flare from light striking the filter surface will be worse. Still, I don't think this is your problem
Do do the flashlight test just to be doubly sure. Not every pinhole shows up every time when simply exposing film. Extend the bellows to the max and check from every conceivable angle.
And, are you really sure you are not just overexposing? A featureless shadow area overexposed will be a featureless denser area... In such cases, the negative will usually print well unless you have pushed the highlights way up onto the shoulder of the film curve. Check the near-shadow (e.g., Zone II and III) areas. If they have the detail you saw in your scene, then you have likely just overexposed, especially if the film rebate is clear (Zone 0).
Keep us posted.