I shoot in the fog whenever I can find it, using Ilford FP4 film and developing with DiXactol, a catechol-based developer. If there is a foreground object such as a tree or rock, I will take a light reading on that with a spot meter and place it on Zone III and usually get a good exposure. If there is no foreground object on which to base a reading, I am left with making an overall reading with a reflective or incident meter. My experience is that it is easy to overexpose negatives in the fog, leading to very dense negatives that are more difficult to print and are excessively grainy. It always surprises me how much light is bouncing around inside the fog.