I bought a Beseler 45MXT, but I am having issues with light falloff at the edges of my prints. After reading around it seems as if I may have to adjust the bellows. but Im still unsure how they should be set, and what I should be looking for in the corresponding light. There is a knob on the upper left side which adjusts the upper belows, and then a knob on my lowe left/right which adjusts the lower belows (i.e. focus). I am printing strictly 35mm with a 50mm lens.