I'm trying to get into LFF with a Crown Graphic. I have twice tried to get the effect of front tilt with a bed drop combined with a back tilt. Both times, I tried to focus the image after dropping the bed, and the back rails on which the lens rides popped out of the guides attached to the box. Although I can fix it, I'm probably damaging the camera. Can anyone offer any advice? How to do this correctly? What am I missing?