Being a long time serious (amateur) photographer, I fully understand f-stops, depth-of-field, hyperfocal distance, focus distance, etc. etc. as it applies to the real world.

I want to use depth-of-field to progressively blur further objects and the background (just like in real-world photography), but what I can't get my head wrapped around is - how can I determine what to set the Focus Distance to.

I Read TFM and it's no help. All it tells you is that the Focus Distance is determined by a 'control object' within the scene and to enter a desired value in the camera's Focus Distance field (the focus_Distance parameter dial for that camera) - What object? What deired value?

My question is - What is the control object, how do I select it and how do I determine what the Focus Distance is?  Any help will be greatly appreciated...

Oh and btw, I'm using P6 and did a quick search but came up blank...

TIA
Walter