Hi, I'm new to medium format and I have a question. I couldn't find the answer in the manual. I use an AE prism. I have the feeling I didn't do the right procedure when using mirror lockup. Do I have set AE lock before mirror lockup? I think with the mirror locked up the way to the prism is blocked so the AE prism is unable to give you metering data. Is that right? Thanks in advance for the answers.