OK – here’s the idea.

1. An IR beam across the entrance to the sluice channel.

2. Flash gun(s) which fire when the beam is broken.

3. Camera shutter to be open when the flashgun(s) fire.

(1) should be easy enough. Could attach the IR emitter and sensor to the wooden beam above the channel, and arranged for the beam to be about 20cm below the beam. Are you looking at the top of page photo? Hmm – how deep is the water?

It is nine years since I last soldered up a circuit, in a previous incarnation as a teacher of control technology. I’ve still got the hardware, but I’ll need to do some research and order some components.

Item (3) is OK. I can either sit beside the camera which is mounted on a tripod and fitted with the remote release, have Bill’s torch playing across the scene, and open the shutter on bulb whenever a bat comes anywhere near the channel. Hope the flash goes off, close the shutter. Alternatively, I can connect the camera to the laptop and run Chris Breeze’s remote control software – DSLR Remote Pro – and set it to time lapse mode, opening the shutter for 5 seconds (it’s pitch dark, remember!), closing the shutter, and repeating till I come back after a coffee.

Say 20 minutes, 20 x 60 = 1200 seconds, that’s 240 images to go through, to find the masterpiece(s) with a bat(s) on.

So I’ve ordered the components!