The manual says you can use any focal plane shutter speed lower than 1/8 with the leaf shutter. Mine won't work at all at 1/8, it works some of the time at 1/4 and all of the time at 1 sec on the focal plane setting. Haven't tried 1/2 second. I don't have the power winder and cock the lens shutter manually. I just developed a roll where I shot three flash pictures outdoors (fill flash). One came out perfectly exposed, the other two were totally unexposed. Even the daylight didn't get through. It seems there is a time lag after the mirror drops and the focal plane shutter opens before the leaf shutter operates. The flash fired each and every time. Seems like the focal plane shutter opens, then closes sometimes before the leaf shutter and flash goes off. I have never got a photo that is partially blocked by the focal plane shutter. It is either perfect or blank. I can put an empty back on, open the lid and verify the whole thing works by seeing the flash through it all. Would purchasing the power winder fix this problem, or is there a problem in the camera or the lens? All focal plane shots with this camera are perfect. I only need the leaf shutter for outside fill flash because the sync speed on the focal plane shutter is only 1/60.