Loading...
These shots were taken during the amazing lightning storm on the night of June 1, 2011. We often get thunderstorms in Boston, but it's usually just a couple rumbles of thunder, a quick shower, and maybe a flash or two in the clouds. This was different - a full lightning storm with many ground strikes. It was amazing, and came with this incredible downpour that just went on and on. These shots were taken just after the storm passed over me, as it was pounding the city south of downtown.
Taking shots of lightning is tricky. Lighting flashes are fast, i.e. short in duration, so it's unlikely for me to be able to see a flash and respond quickly enough to press a shutter, especially with the shutter delay. So how to consistently capture shots of lightning?
The only approach I can think of is to set up a camera on a tripod, and take long exposures, arranged such that if a lightning fork occurs in the field of view during the exposure, it can get captured. The key is exposure, and this is where my long hours diddling round with manual flashes really came in handy, because the principles are exactly the same. When using flash of constant intensity, the flash very briefly illuminates part of the scene, and only actually only accounts for a tiny part (1/10,000th of a second) of the time that the shutter is open. This makes it possible to capture really events in an instant of a second, even though the exposure is actually quite long, and is how I and others are able to capture exploding test tubes and so on (see the post from last week). In an exactly analogous manner, the brightness or luminosity of the lightning fork in the image is exclusively determined by the f/stop and the ISO. Thus, I think the appropriate way to capture lightning is to first expose for the lightning (f/stop and ISO), and then choose a shutter setting to expose for everything else.
For example, let's consider the third image, multiple strikes behind the Museum of Science. This was taken at ISO 200, f/11, 15 sec. The exact ISO and f/stop settings are determined by the average brightness of the lightning flashes (which depends on the storm). Given those conditions, 15 seconds is how long it takes to make a reasonable exposure of the Museum of Science, and to keep the sky relatively dark. What would have happened if I had exposed for 30 seconds? Well, the lightning fork would look to be the same intensity - it happened over a tiny amount of time over the exposure, so leaving the shutter open longer doesn't make it any brighter. In contrast, light from the Museum continuously falls on the sensor. So, if the exposure is twice as long, the Museum is twice as bright. Also, light from the sky continuously falls on the sensor, so if the exposure is twice as long, the sky is twice as bright. I thought that would take away from the impact of the shot, so I made the shorter 15 second exposure instead.
How to actually set this up? I set up the camera on a tripod in a sheltered location, and hooked up the camera to my laptop with a USB cable. Canon supplies a remote software with its camera, which lets me set all the exposure settings from the laptop. In addition, the software can be set to continuously take new photos. It takes about 2 seconds between shots for the software to reset itself, so I set the computer to trigger a new photo every 17 seconds. Since the shutter is actually open for 15 of those 17 seconds, I know that I'm capturing 88% of the lightning forks within the field of view of the camera. This is a shitload better than what I could have achieved by trying to trigger the shutter every time I saw lightning. With the software taking care of all the actual exposures, all I had to do was relax and enjoy the show.
