OneStep actually refers to the camera, not the film. There were two generations of OneSteps; the first took SX-70 film, and the second took 600 film. The easiest way to check which film you have is to open a box and try to stick it in the camera. If it slides in smoothly, it's SX-70 film, if it hangs up about 1/3 of the way in, it's 600. If it's 600 film, you'll have to use an ND4 filter in front of the lens, use one of these filters on the pack, or do what Whitey says and remove the ND filter from the lens and move the black and white wheel all the way to black.