Photoshop Lens Blur Effect

[Joey]

Since I do a little rendering I loved that effect since it enabled me to easily get depth of field without leaving that to the renderer (which greatly prolongs render times). Anyhow, I wanted to try implementing that effect for Paint.NET and after finally understanding how convolution works and in which way one can avoid using integrals I came up with some code that works pretty similar to the Unfocus Effect. Results are not exactly equal and my code is way slower, so I thought I could maybe utilize Unfocus.

Now the Lens Blur filter utilizes a depth map which you could either hand-paint for photos or easily generate with 3D applications for rendered scenes and simulates depth of field while you can select where the focus lies. After looking how Unfocus worked (and trying to grasp what was done there with pointers) I think I would be unable to feed that code with varying levels of blurriness. Or may that still be possible somehow?