I'm new to this forum and I'm hoping someone out there can help me. I bought a Mamiya RB67 ProS today. It came with the 150mm C soft focus lens and a battery driven back that can use both 120 and 220 film. It didn't come with any of the manuals. I found and downloaded the appropriate camera manual but I can find nothing on using the battery powered back. Any assistance would be greatly appreciated. Thanks.