Specifying the range for Depth of Field (MeshDepthMaterial range?) - three.js

Question

I have adapted this post processing example http://mrdoob.github.com/three.js/examples/webgl_postprocessing_dof.html to apply a Depth of Field / Bokeh effect. How can I specify the focus range (or whatever it could be called)?
If the camera far plane is at 10000, and the model size is 10 it was impossible to focus into invidual parts of the model - because it tries to focus from 1-10000 (camera-near to camera-far) instead of 1-10 (between camera and the back of my model), the actual area of interest.
It did work fine after I realised to set the camera far plane as low as possible (to about same as scene size), so the focus can adjusted where the actual model is.
Now I can't do the camera far plane trick anymore, because I added a skybox, so the camera needs to have it's far plane quite far related to the model size. That messes up the Depth of Field; I can focus very close or very far, but the whole model is either completely blurred or not blurred at all as the adjustable distance is way too big (all the way to the skybox).
If I know the area I want to be able to focus at, how can I specify it in my code?
Here is my setup code:
dof_material_depth = new THREE.MeshDepthMaterial();
dof_scene = new THREE.Scene();
dof_camera = new THREE.OrthographicCamera(SCREEN_WIDTH / - 2, SCREEN_WIDTH / 2, SCREEN_HEIGHT / 2, SCREEN_HEIGHT / - 2, -10000, 10000 );
dof_camera.position.z = 100;
dof_scene.add( dof_camera );
var pars = { minFilter: THREE.LinearFilter, magFilter: THREE.LinearFilter, format: THREE.RGBAFormat };
dof_rtTextureDepth = new THREE.WebGLRenderTarget(SCREEN_WIDTH, SCREEN_HEIGHT, pars );
dof_rtTextureColor = new THREE.WebGLRenderTarget(SCREEN_WIDTH, SCREEN_HEIGHT, pars );
dof_bokeh_shader = THREE.BokehShader;
dof_bokeh_uniforms = THREE.UniformsUtils.clone(dof_bokeh_shader.uniforms );
dof_bokeh_uniforms[ "tColor" ].value = dof_rtTextureColor;
dof_bokeh_uniforms[ "tDepth" ].value = dof_rtTextureDepth;
dof_bokeh_uniforms[ "focus" ].value = 1.1;
dof_bokeh_uniforms[ "aspect" ].value = SCREEN_WIDTH / SCREEN_HEIGHT;
dof_materialBokeh = new THREE.ShaderMaterial( {
uniforms: dof_bokeh_uniforms,
vertexShader: dof_bokeh_shader.vertexShader,
fragmentShader: dof_bokeh_shader.fragmentShader
});
dof_quad = new THREE.Mesh( new THREE.PlaneGeometry(SCREEN_WIDTH, SCREEN_HEIGHT), dof_materialBokeh );
dof_quad.position.z = -500;
dof_scene.add(dof_quad );
And here the rendering part:
renderer.render(scene, camera, dof_rtTextureColor, true );
scene.overrideMaterial = dof_material_depth;
renderer.render(scene, camera, dof_rtTextureDepth, true );
dof_scene.overrideMaterial = null;
render(dof_scene, dof_camera );
var delta = 0.01;
composerScene.render( delta);
EDIT:
I did manage to get desired results by setting a low far plane for the camera just before rendering the depth material, then reverting back to normal before rendering the composite:
renderer.render(scene, camera, dof_rtTextureColor, true );
var oldfar = camera.far; // this goes to skybox
camera.far = scenesize; // this goes to just behind the model
scene.overrideMaterial = dof_material_depth;
renderer.render(scene, camera, dof_rtTextureDepth, true );
camera.far = oldfar;
dof_scene.overrideMaterial = null;
render(dof_scene, dof_camera );
var delta = 0.01;
composerScene.render( delta);
This works perfect. I will leave the question open though, as I'm quite new to WebGLL / 3D programming in general, want to learn, and would like to know if it's possible to do this in the shaders/materials setup phase.