My thoughts were he wanted this in a small package that was connected with the camera.

How about just a small transistor radio?
And if you plug into the headphone output for the detection circuit, it likely kills the speaker.

 

My thoughts were he wanted this in a small package that was connected with the camera. Like the ones you can buy.

Adding the optoisolator and the reed relay, and even a transistor can all be wired up and encased in a glob of epoxy on the back of a small transistor radio. That is about as small a package using standard sized components as I can think up right now.. AND, since the radio would need to be tuned to a quiet spot to work right, noise should not be a big concern. In fact, probably it would be desirable so as to verify that a storm was "making sparks."

 

1.- in http://www.discovercircuits.com/S/sou-operate.htm

there's a bulky 40kHz 'clap' detector

http://www.webx.dk/oz2cpu/radios/sound-light.htm

that precisely operates a light switch on catching audio clpa-like input.

Since you've mentioned the photograph role such box may be impractical to carry around.

2.
single clap relay actuactor

https://www.electroschematics.com/11010/clap-switch-circuit/

John BG

 

Radio waves travel close to the speed of light, while sound travels a whole lot slower. A sound triggered camera would miss the lightning every time, by quite a few seconds. Using the "clapper" switch with an antenna is an interesting concept, though. I am guessing that is what you are thinking about in the post.