I first sketched this out in pencil, followed by rendering it all using a technical ink pen with my cross hatching and pointillism technique. Then I scanned it into the computer and digitally enhanced everything in Photoshop using a graphics tablet. Intensive but it gets the results I'm after.
A larger image can be found over on Twitter.
You can appreciate the depth of field better in the larger size. This close up section gives you some idea of the effect: