Professional grade high speed electronic flash units are available but in keeping with my theme of Do-It-Yourself frugality, I'll show you how I made a small change to a simple electronic flash that forces it to "fire" at its shortest time interval.
First very basic understanding of the flash unit is necessarily. Rather that rewrite it, I'll encourage you to visit the Wikipedia article on the electronic flash.
OK, got that? The key to the process is that when the capacitor discharges, the flash tube lights up for a specific length of time. On more modern flash units, that length of time is variable. In times past, with a flash that fires for a set amount of time, it was necessary to determine the proper f/stop by measuring the distance to the subject and performing a calculation using that data along with film speed and the guide number of the flash.
With the variable speed flash, this became much easier to do. These units usually had a film speed setting on them and contain a photocell that reads how much light is reflecting back from the subject. When the flash tube was illuminated, the photocell would turn off the tube when sufficient light had been detected. The closer the subject, the more light that is reflected back to the photocell yielding a shorter exposure time. It is that feature we will exploit.
The flash unit in our example is a Sunpack Auto322. The range of time that the flash tube will illuminate goes from 1/1300th to 1/20000th of a second. All we need to do is to make the photocell think that the subject is as close as possible, a trick that only requires a bit of paper and some tape.
See the pictures below for how to do this.
Be sure to see the pictures created with this technique in the Freeze Frame Gallery.
Click on the pictures below to enlarge them.
The red arrow is pointing at the location of the photocell on the flash unit.
This is the paper loop that will direct a portion of the flash directly to the photocell.
This is a close up of the paper loop showing how little of the flash is needed to be directed to the photocell.
This flash unit has both a "hotshoe" and a cord that can be used to fire the flash. The end of the cord is some kind of male flash cord thing. To wire it up to your own project, just acquire a flash extension cord and connect its female connector to the flash's male, cut off the male connector on the extension cord, and cut back the insulation to expose the wires. Shorting the wires together will fire the flash.