So I found a Hasselblad 500C on CL for $300 ... with the Planar 80, 12 back (not A), 24 back, WLF, assorted filters, and some random film (some Tri-X, color slide film/chrome, and something else....) and I bought it. I am NOT familiar with the Hasselblad system, let alone the 12 back - so the first roll I ran through it I wasn't surprised when it came out blank. I watched several you tube videos on how to properly load the tricky 12 back; and the second roll I made sure that I loaded correctly - watched for the 1 through the peephole and then set the counter at 1. When I took the first shot on the roll, I noticed that I had forgotten to take the dark slide out. But the shutter fired anyway! So - I ran the roll - developed it - and nothing AGAIN. Totally blank. No exposures at all. So I tested the camera AGAIN. Watched the shutter fire - checked the rear curtains/flap - everything that I found to do on this forum to check the camera. I even tested the dark slide and it DIDNT fire with it in while testing. It seems to work fine as far as that goes. So my question is - would an improperly loading back cause blank negatives? When I completed the roll - the film was advanced to the takeup spool. So it DID advance. But why would it fire with the dark slide in while loaded with film but not when dry firing to test? What can I do? Keep in mind that I have contacted the seller and am asking him what I should do as well; so there is a possibility of returning it (he said he had lots of inquiries from his listing, so I'm sure he could sell it to someone else...). Thanks for any and all info!