If you hit “I” in the buttons window for the camera, you can key the focal distance (in addition to clipping and lens)
Thanks to eeshlo! You finally made it man!
Here is my first contribution for a rather long time, but I had to play with the defocus node 
I’ll post a animation later, if the file is not becoming too big.
mmmm, bokeh 
Hi,
I’d like to know where I could post a wish to make a little (hope so!) change on the defocus node. I’d like an easy way to change the focus distance, like photoshop’s lens blur has. I’m using rendered inputs + zdepth greyscale images, so changing the camera values won’t work.
Use the time input to animate the mixing of 2 zdepth inputs. Its kinda clunky but it works.
is there not already a node to do this? like ‘map value’ perhaps? there are a lot of powerful features lurking in the node compositor…
Yes, to get the focal plane input the zbuffer into a color map node. Make the color map gradient white with a black band in the middle. The black will be in focus and the white out of focus. You can move the black bar to vary the effect. Feed two of these into a color mix node using the time node for the factor of the mix. The result of this mix goes into the z input of the defocus node.
yups, but this gives bad artifacts on the modified zdepth map node… or I am doing it wrong?
I add a slight blur on the resulting z output before sending it to the defocus.
thread is two years old guys!
.b