Rural Areas at Night: Focus at infinity, F-stop of F5.6. When lightning gets very close (within 1 mile, less than 5 seconds between flash-thunder), use an F-stop of F8. You'll also want to use F8 if you want to expose multiple bolts over a long period of time (see note below). In rural areas with little or no ambient light, you can leave your shutter open indefinitely until a lightning bolt flashes in your frame.

Urban Areas at Night: Focus at infinity, F-stop of F5.6 for a maximum exposure time of 15 seconds or so. Or, F-stop of F8 for 20 to 35 seconds. For best results, expose the scene as you would without lightning, and the lightning will take care of its own exposure when it flashes in the background.

Daytime Time-Exposure: Focus at Infinity, F-stop of F8. Use three-second exposure intervals. This uses film up very fast, and generally has a low rate of return. You should only attempt this with the most intense lightning storms containing frequent strikes. Also, a bolt caught using daytime time exposures will only show up well if it is very close (at right).

Daytime or Nighttime Reflex Exposure: This method can be used with any type of camera, not just an SLR. Aim your camera at the scene, keeping your finger on the shutter button. As soon as you see a flash, hit the shutter immediately. Most lightning discharges are made up of multiple, repeated return strokes. While your reflex action will miss the first (and the only branched) stroke, you have a good chance of capturing one of the subsequent strokes. Furthermore, it is common for several separate cloud-to-ground strikes to occur in rapid succession, each triggered by the one before (see this video clip). If you react to the first one, you may very well catch one of the subsequent ones.