I picked up a Bronica SQ a couple of months ago from a APUGer, and started shooting with it -- nice camera. But I found that I'd forget to pull the dark slide and the camera would still me let me fire the camera. I kept losing pictures as I'd forget to pull the slide before making several exposures. "Oh, great," I thought, "I bought a defective camera or back." I googled to find out how to fix the problem, read about the various pins on the back that interface with the body, and so forth. Nothing seemed to work. This morning, after again making blank exposures, I was taking out the roll of film and happened to notice that by the top of the dark slide slot in the back was a small white circle with a dot inside. I then looked at the plastic handle on the dark slide and saw that it said "Bronica" on one end and had the same circle/dot figure on the other. Bingo -- Bronica wants me to match the two symbols when inserting the slide. I did, and the camera would no longer fire with the slide in. I looked closely at the slide and saw near the plastic handle a small cutout that obviously interfaces with the internals of the back/body interface. So if you've had the same "problem" try this fix -- put the dark slide in correctly.