High Speed Photography - the poor man's 5 minute bullet switch
This is the heart of the high speed photography setup - the event trigger. The cardboard was a square piece, ripped off a shipping carton (Thanks, Digikey Corp!) with a 4" x 6" or so rectangle window cut out the middle. It's the standard 1 ply corrugated cardboard. On both sides are taped a sheet of aluminum foil, held on with blue painter's masking tape. I happened to just have a roll lying around in my shop.
Wires connect the foil pieces to pocket wizard - actually, I used the FlashZebra pocketWizard hot shoe adapter, but this time around, the pocket wizard itself is plugged into the hot shoe. I didn't want to gimp a perfectly good adapter, so I just stripped off about 4" of insulation and wire wrapped the bare wire around each of the terminals on the phono plug, and masking taped it down. My perfectionist electrical engineering Dad would disown me if he saw the wiring.
The PW is actually a multi-max. It is set to delay-trigger. This part is key; we can dial in at 0.1ms (1/10,000th sec) interval the delay between when contact is made and when the flash fires - allowing the projectile time to reach its intented target.
I'm using the Irwin clamp here for two reasons; to hold the bullet switch up and most importantly to keep the electrical contact nicely seated. The bare wire just touches the foil underneath the clamp - nothing fancy. In my next version I'll actually add a spring battery clip, but for now, this works.
Firing through the two pieces of tin foil closes the electrical contact - then starts the millisecond delay (we used 6.5 ms, but this will depend on the gun's muzzle velocity and the distance to target). This number was arrived at with rough back of the head calculations followed by fine tuning of the numbers.