I've been working on a project of environmental portraits taken in cold rooms/wine cellars using TMY-2 in 4x5. On three occassions my negatives turned out having a "fogged" area near the center. Very difficult to see on the negative but it turns out clearly visible in the print or scan. This only ever happens when I'm using my Nikkor SW 75mm lens. However, this lens has taken many other pictures with no such problem. The only explanation I could come up with is condensation on the film in the film holder or on the lens itself. My holders are always kept in ziplock bags just before taking the exposure. On all three occassions the weather was hot and humid outside. The inside of the celler is much cooler, and two of the cellers were air conditioned. I'm wondering if this is a problem others have encountered, and whether it is more likley to be condensation on the lens or on the film? Why would the condensation only occur near the center of the image, and does this distinguish between film and lens as the culprit? I attached a picture showing the fogged area directly to the right of the subject.