Lightning Activated Camera Shutter Trigger
This was the link that set me thinking that there must be an even simpler way.
Essentially - you need a photo transistor, monostable IC, relay driver and a relay.
I came up with the circuit shown in the attachment to post #10 of this thread. I'm not a electronics's designer so it could be improved a diode across the relay coil etc.
Every thing was at hand apart from the photo transistor and the 2.5mm plugs / sockets needed to modify the camera's remote release cable.
It works very well as seen in the other attachments and it was also extremely easy to build. The 1 pole 8 way switch shown in the circuit was just an 8x single pole DIL switch the sort that fits into a 16 pin IC socket.
Obviously you also need a 9v battery and on/off switch.
I hope to get a scrap flash unit were I can just use the case, then it will be easily mounted onto my camera's hot shoe.