This weekend I tried taking photos of fire and smoke: two objects that are fairly common this time of year, but are also vary unusual in that they do not have two essential visual elements (in the traditional sense): shape and form. I didn't want to work with (say) a candle flame or incense stick- those have been done to death. Go big or go home!
I approached these subjects from the scientific perspective, based on my exposure to them back at NASA- both are multicomponent fluid flows. Fire is a chemically reacting multicomponent system with strong thermal gradients, while smoke (soot) has electrostatic interactions. When imaging fluid flow, shutter speed is the dominant consideration- and for inspiration, you may want to check out Physics of Fluids "Gallery of fluid motion" for some really excellent examples:
http://pof.aip.org/gallery_of_fluid_motion
Of the two, fire was much easier to photograph. First, work with a long lens- I used my 85mm f/1.4, but a 100mm macro may be even better. Second, manual focus only, and you probably want to work in shutter priority mode or total manual mode if your camera likes to think. I noticed that no matter how fast I set my shutter, the image improved, so I worked at 1/8000 s (the fastest I could go) exposures only. Since fire is luminous, I could get away with this. However, I also had to use the lens wide open in order to get sufficient light, so the depth of field is small. In any case, here's a few examples:
[PLAIN]http://img214.imageshack.us/img214/7376/dsc2085.png
[PLAIN]http://img18.imageshack.us/img18/2789/dsc2078.png
[PLAIN]http://img545.imageshack.us/img545/2218/dsc2084.png
I like the textures- the flame fronts appear as a flexible sheet, and it's totally invisible to the eye.
Fire is the easier to photograph because it doesn't move. That is, the fire is changing, but the location of the fire doesn't move. Smoke, by contrast, was much harder to photograph since each 'puff' stuck around for only a few seconds. Creating laminar flow conditions is essential, and the other essential part is to light from the side. I got reasonable results at 1/1250s exposures, but again I had to work at f/1.4 and ISO 1600 to get enough light on the sensor. This led to the main trick- I left the lens as close focus (2 feet) and constantly moved around in order to get anything of interest in focus.
[PLAIN]http://img11.imageshack.us/img11/6522/dsc2181.png
[PLAIN]http://img638.imageshack.us/img638/7668/dsc2018.png
[PLAIN]http://img522.imageshack.us/img522/5620/dsc2221.png
I think I could get better images by going with a short focal length lens to increase the depth of field- the smoke tendrils/sheets are fairly large and move in all three dimensions.