Ken i apologize for not reading the post abit more closely. I would agree with Jorge that it may be an exposure problem since you describe the density change in the middle of the neg. One other possibility could be film holders. I recently bought a 4 used riteway film holders and after using them had a couple negs with the same problem you describe but showing overexposure indicating some sort of a light leak. In any event once a narrowed it done to the offending holders the problem was eliminated. Just another possibility.(posted 8421 days ago)