[chrisnason]

The web page circuit was very complicated with high pass filters etc. but it showed me that idea worked. It dated from film times so wasted shots were expensive!
I thought I would experiment with odd spares I had, only needing to buy the phototransistor from Maplins £1.80?
The phototransistor was rubber sleeved on it's sides and rear then just hand pointed in the storm direction, I found a trigger resistor of 4M7 was about correct for the light that evening. The phototransistor could be attached to the view finder. As we don't get many storms here in Sussex England I've only had one chance to experiment.
The 1uF cap closes the relay for about 1 sec so it could be reduced to a much lower value but it worked and it was easy to see the monitor LED going out, when the relay closes.
In the next storm I will try continuous shooting mode, a 1 sec burst of shots might be interesting. I believe a single flash can last 0.3 sec.
I used a wide angle lens with the camera in full manual mode F5 (fastest), ISO800 and around 1/20 sec. manual focus. This gave good fine detail in the lightning and only over exposed in one of the 4 successful shots.
Mirror lock-up mode would improve the response even further - I need more storms to experiment with!
It seems difficult / expensive to get a plug for the external shutter connector on my Canon 20D which is why I modified my cable.
The other 3 photos attached