Depth Of FIeld - howto achieve it

Totally new with Fusion. I'm trying to use depth output to get depth of field effect in fusion - and I fail badly.
I've added final color render from 3d app and depth output (both 16 bit exr). THen added "channel boolean" node and connected both images to it (color to BG , depth to FG). In the node setting I've set R, G, B , Alpha to "Do Nothing" and in Aux Channels I've marked "Enable Extra Channels" and set Z buffer to "Lightness FG".
THen connected those to DepthBlur node. Seems to do nothing - sliders do not change a thing. Also I'm not sure how the "Pick" button should work - pick what/ where?
Lastly - when dragged depth output image to the view I got a white image for the objects. But that was expected - as soon as I switched to normalized view I got those nice shades of grey.
Any suggestions howto work with this node greatly appreciated - definitely prefer to save render time and get this depth of field effect in comp.

View the "depth blur" in a viewer, click and drag from the "pick" button into the viewer where you want to have the focus

can I ask, I'm having a similar issue, I'm relatively new to Fusion however I am sure the node tree is having a similar issue. It seems to be piped correctly, and with the depthblur in viewer - dragging the pick tool shows zdepth values that vary, however the blur seems to consistent, and even with an a/b comparison, still seems completely in focus. I can blur all of the scene, but not using the Zdepth, am I doing something stupidly wrong? my channelboolean is reading an extrachannel zbuffer - lighness FG vray pass. tutorials online haven't helped either...

anybody? please ...

You can't pick the values off the output, you need to pick it off the input.

I was struggling with that for a while too...
Keep in mind that the values in the distance field are extremely sensitive, and adjusting the slider is basically useless, since the change per pixel are huge, so you have to insert the values manually and increase/decrease in decimals.
Also, at least on Fusion 8 for the mac, the picker is broken.