Here’s another video tutorial teaching how to give your bokeh custom shapes.
When a point of light in a photograph is out of focus, it turns into a shape defined by the lens’s aperture. We can create a second, smaller, aperture to attach to the front of our lens in order to customize that shape. The result is a charming effect in the background of your photographs, as long as there points of light such as streetlights, candles, or Christmas lights in frame. [#]
You can also find a text version of this tutorial here.