Because lightning strikes happen so fast,
it's simply impossible to press the shutter button
when you see the lightning.
You'll take a picture of empty darkness every time.
You need to create a larger «net» to catch lightning bolts, which means using long exposure times. If lightning strikes during your exposure, your camera will catch it.
Exactly how long you should expose the picture depends a bit on the conditions, but the picture shown here had a 4 second exposure time at F4 opening to give you a starting point.
You can’t use extremely long exposure times because with the settings needed for very long exposure, your camera will not catch enough light of the very brief lightning strike.
So in practice:
— set your camera on a tripod, or place it on a solid surface where it will not suffer any movement or vibration.
— set the ISO sensitivity to 100, for long exposures higher ISO settings will create more «noise» in the picture.
— your aperture will decide how bright you will capture the lightning strike. F4 is a good starting point. The exposure time will then depend on how much light there is in the rest of your background. If you're shooting a well-lit city, exposure time will be only a handful of seconds. In a darker setting, you can stretch the exposure time much longer which increases your chances of success.
— if you do not have a remote trigger, you can use the 2-second shutter delay function. Basically your camera will wait for 2 seconds after you press the button to take a picture. This is important because when you push the button the camera will shake very briefly which can mess up your exposure.
— finally, you will want to make as many pictures as possible, pressing the shutter again as soon as the exposure is finished. The more time your shutter is open, the bigger the chance to catch lightning.
Unless the lightning strikes are occurring very frequently, be prepared to spend some time until you catch that one nice shot!
The lightning strike over central Bangkok took about 1 hour to catch, since lightning strikes were few and far between.