Too strange, I came here today to ask a very similar question. I borrowed a Metz 45 CL-4 to shoot with my Yashica-Mat LM. used a PC cord, set to "x" and dialed in the ISO and aperture on the flash. As I was shooting, all looked great and seemingly working fine. I processed my Velvia 100F late yesterday and took a look this morning. There are images, but extremely dark. Without a loop you would think it was just black. I believe I was set on 1/50 speed, but I was under the impression that if a Yashica TLR was set to "x" it would sync at all speeds. This this so?