Smoke, part 2
We don't normally "see" smoke. The minute particles that make up smoke are something that turn up in your photograph as an obstruction, as atmospheric haze, blocking the light you want, or sometimes creating spectacular sunsets. But it's the light you focus on, not the smoke.
After 122 photos, spread over 3 days of trying, I've finally got images that I like. The lack of sharpness was solved by shooting at f8, and the noise was cleaned up by judicious use of a brush. I figured out that I didn't need backlighting - straight-on flash works perfectly fine (this I "figured out" by having my external flash fail to slave properly to the camera). The 3 step solution is now:
1) black background a fair distance away from source of smoke (helps smooth out the background, which you want as evenly black as possible)
2) set camera to f8, flash, manual focus on the smoke
3) processing: invert image, clean up background, adjust levels (I set the white point on the "grey-est" part of the background to make it even more evenly white), muck around with colour balance to get the tone you want. Sharpening is optional.