FC writes:
This circuit is used to trigger a camera’s electronic shutter circuit when a flash of lightning is present. This circuit would also work for photographing fireworks displays or other events involving flashes of light. In a nutshell, the photo darlington converts light pulses into electrical pulses, the first LM324 section amplifies the electrical pulses, the second LM324 section is a high pass filter that only passes quick changes (lightning). The third LM324 stage is a comparator that allows only large pulses to pass through, and the 4047 one-shot stretches out the length of the pulses so that they are long enough to drive the relay and trigger the camera.
Continue reading at SolOrb.com (includes schematic)
Via MAKE Blog