I have my father's old Rollei. I've never used it but it seems operable, so I thought I'd give it a try. Unfortunately, I can't figure out how to get the back open. Extensive Googling provided no answer. There is a lever at the bottom that I suspect gets pushed towards the camera's top or, more likely, downwards if you're holding the camera upright. But I don't know which, if either, and I don't want to break it. Any help would be appreciated.