I'd downloaded the manual ysterday in an attempt to find out what to do with this switch. I found the diagram that explained what to do with the F4 F2 dial but couldn't make out why I should need to use it. I was reading it on a mobile phone which didn't help. As far as I can see now, it has to do with the autofocus lenses that could be used with the Om30. As I only have manual focus lenses, I'll probably never need to use this control.