I was shooting a Polaroid test for an abstract b+w series and the neg flipped back onto the print out of register. This was not really the effect I was originally looking for, but it appealed to me in a certain way. Shot on Sinar F1 with Ross Xpres 6 1/2" f2.9 and Day shutter, exposure 1/40 @ f2.9, lighting by modeling light of studio flash (actual flash too bright to allow desired aperture of f2.9).