I have a small set of Kodak 9x12 holders that I just received in the mail. Unlike my others (Voigtlander & Zeiss holders) which are clearly for plates and take film sheaths, these are a little bit ambiguous. There's a spring loaded back that presses up against a frame to hold (film? plates?) in place. There's a fair bit of room when you press the spring plate back, so I'm not sure if this was designed for plates or film. In short; do I need a film sheath for these or will they work as-is? They look like they would secure film in place, but I'm not totally sure how much slop there would be, if the film will be planar and aligned with the focus plane, etc. Also, they have a bit of a recess in them; you can see in the images how the border of the pressure plate is raised relative to the center. Images attached. Perhaps someone else uses these as well.