Depth Of Field

hello everyone, sorry for the trivial question, but I still don't understand how it works, then I would like an effect similar to this, when I examine an object, that is when I click the "t" key, the object is examined, so yes approach the room and I would like to give this effect in the photo, how can I do?
the image I took from the web, but the effect I would like is this in the picture.
I tried to access the various parameters like this:

Code (CSharp):

1.                     DoF.nearFocusStart = new MinFloatParameter(6f, 0f, true);
2.                     DoF.nearFocusEnd = new MinFloatParameter(9f, 0f, true);
3.                     DoF.focusDistance.value = 9f;
4.  
5.                     DoF.farFocusStart = new MinFloatParameter(0f, 0f, true);
6.                     DoF.farFocusEnd = new MinFloatParameter(6.6f, 0f, true);

but I was unable to achieve this effect.
ah, I use HDRP as the Pipeline.

 

@Olmi