First light on my new wooden 4x5, using FP4+. Getting a slash of light across the bottom of the negatives, but only when using the camera in vertical (portrait) mode. Since it happens with all film holders, and doesn't happen in landscape mode, I'm ruling out film holder problems, and suspect some sort of inside reflection. I'm new to pinholing, would appreciate any ideas. Please ignore the poor exposures, I'm still figuring this stuff out.