First, to verify even illumination, use a SPOT meter and meter the corners and edges. Except for flash meters, incident meters are useless! (Phil Davis not withstanding!) But it sounds like a lack of coverage from your enlarging lens. A 135 mm lens will NOT cover a 4X5 negative; you need a 150 mm. That should fix the problem. Uneven developing will show very uneven areas all over the negative, not just the edges/corners. Good luck.(posted 8976 days ago)