I have a question for those of you who have experience using a Plasticca lens. Have you tried using the cell mounted on the back of the barrel, as opposed to the front? The soft focus/diffusion effect appears quite different in that configuration. With the cell mounted on the front of the barrel (as designed, the convex surface facing toward the subject and away from the film plane/ground glass), the image appears relatively sharp in the center, but falls apart off axis. There doesnít appear to be much diffusion in the central sharp area, and the off-axis areas looks defocused, like very severe field curvature. With the cell mounted on the back of the barrel (the convex element facing the film plane/ground glass), I see a nicely diffused image relatively evenly spread across the image, even in the center. I think itís neat that you can create such different effects by simply moving the cell from front to back, depending on your preference. What optical principles might account for this?