Are these interior or exterior interviews? How far from the background is your talent? How open is your aperture? Focal length plays one part in DoF; aperture width plays another.

I was actually the subject of an interview shoot a few months ago and the production company who shot our office put up a black, open weave material (akin to bobbinet or shade cloth for use in gardens) to increase apparent DoF behind me as the interview subject. I'd guess the camera was 8' away from me, and the material was about 2' behind me...I don't know what their camera settings were. I'll be testing this myself soon, but just a note that I've seen scrims used to blur backgrounds in person and in the resulting footage, and it does indeed look really quite convincing, bokeh-wise. Apologies, I don't know the name of the material.

Hi, the camera should be not 2 close to the interviewed kid right?The more the iris is open the more the Depth of Field decrease right?
Correct me if i'm wrong

thxMM

You are correct about both. If your subject is too close, they may be outside the minimum focal distance, thus they will be out of focus.

And a wider iris (more open) does contribute to a shallower DoF. A long focal length also contributes, which is why DoF becomes more shallow the farther you zoom in. What also happens is a compression of Z space, which means the perceived distance between foreground and background appears to be less.

Any example about the rules of this important technique?