It's made by another gentleman, consists of a simple but nicely crafted solid walnut box using dovetailed joints. 79mm focal length, 0.020 pinhole @ about f/158. Has tripod mounts for vertical and horizontal. The shutter is my fingertip. I have many film holders, and it's doing it with any of them--but only in the portrait position. FH's are held by large flat plastic "nut" on a stud, one on each side of the camera back. The light seals are sticky-back felt, so maybe I'm tightening the hold-downs too tight and warping the plastic body of the film holders causing them to pull away a little on the dark slide end. Still doesn't make sense to me that it doesn't happen in the landscape position, though, since I don't do anything different other than change the camera's position to horizontal and use the other tripod socket. I'll try a couple of heavy rubber bands at the top and bottom of the film holder and just lightly tighten the hold-down screws, and see if that helps.