I am trying a long exposure using a Kodak 3.0 ND filter (10 stops) and constantly get excessive film fogging. It is a 4x5 camera and one of the Nikon gel filter holders that screws into the lens, so there isn't a gap between filter and lens for light to leak in. I am using a compendium shade to keep flare light from striking the filter, but I still get a lot of fog. The edges of the film are clear like normal, but the shadows are dense with no information. If they had any, I would say that my reciprocity correction was too generous and I was getting overexposure, but the shadows are featureless yet overly dense. Any thoughts? Would putting the filter behind the lens help perhaps?