I got my sx-70 in the mail monday! Looks pretty cool. My time zero should arrive tomorrow! So I embark upon a new photographic experience... A couple things: 1. What is the little knob on the left for? I can see it spinning something open and closed, but I don't know what it does. 2. How long would you recommend waiting after exposure to begin manipulating for the first time? What's a good beginner time? Thanks!