Project for Individual Study: Stop a Bullet

If you're at all serious about photography, you've seen and, perhaps, studied those stroboscopic pictures of bullets stopped in mid-air, light bulbs captured in the act of breaking, or droplets of water frozen as they erupt from a bowl, as you can see in Figure 5.37. Your project for this chapter is to explore the world of high-speed motion stopping. Your digital camera and a little ingenuity may be all you need. I'll give you some tips to get started in this section.

Figure 5.37. Frozen droplets like these call for very, very fast shutter speeds or the action-stopping capabilities of electronic flash.

Strobe photography takes advantage of the very brief exposure times afforded by electronic flashes. As I mentioned earlier in this chapter, the closer an automatic flash is to the subject, the shorter its exposure is likely to be. You might be amazed at the range of fast-moving objects that can be captured by a single exposure. Here are the key ingredients of your project:

• A tripod-mounted digital camera capable of long or time exposures, and which accepts an external flash unit.
• A darkened room, so that the only exposure comes from the flash itself, not any ambient illumination.
• A dark background. A piece of common black felt fabric should work fine.
• An electronic flashgun with user-settable power levels and a removable flash cord. Some flash units can be adjusted from full power down to 1/64th power or less. A flash with less power and a briefer flash duration would be preferred over a heavy-duty flash unit that's hard to scale down for close-up photos, and which has a longer flash duration.
• Optionally, a second electronic flash equipped with a slave unit so it can be triggered by the main flash, and also with low power/brief duration options.
• A subject to photograph. Some prefer hummingbirds, others like to break balloons or light bulbs, or capture coronas of liquid droplets arising from a smooth surface. Choosing an ingenious subject is part of your assignment. Use your imagination.
• If you're planning to destroy something for your photographic art, you'll need a triggering device that can set off the flash at the moment of destruction. I'll give you some hints on how to construct one.

The Basic Steps (Oversimplified to the Extreme)

Once you've assembled all the components, you'll need to plan your photograph carefully. The following is a checklist of how you might take such a high-speed photograph.

1. Set up your camera in a room that can be darkened, facing the black background. You're going to use a time exposure to make the picture, so you don't want any existing light to spoil the image.
2. Put the digital camera on a tripod, facing the dark background.
3. Place your subject between the camera and the background.
4. Arrange your electronic flash unit (or two) so they are on one or both sides of the camera, facing the subject. The second flash can also be used from the side to provide more interesting illumination. In fact, you can use one flash as a main light and one as a fill light, if you like. See Chapter 6 for instructions on this kind of lighting.
5. Set the electronic flash for its briefest exposure.
6. Set the camera's aperture so the image will be properly exposed by the flash. You might have to calculate the correct f-stop through a little experimentation.
7. Darken the room. You should have planned the next few steps so you can handle them in the dark.
8. Open the shutter of the digital camera for the time exposure.
9. At the right moment (more on that in a moment!) trigger the flash.
10. After the exposure, close the shutter of your camera and turn the room lights back on. You're done!

Indeed, the whole process seems fairly easy, except for Step 9. How in the heck is that managed? My list above is a little like providing a recipe for broiled unicorn, and listing Step 1 as "find a unicorn."

The Hard Part

I didn't mean to throw you by making everything seem easy up until Step 9. In practice, triggering the flash at the right moment is the real killer roadblock of high-speed photography. Sophisticated triggering mechanisms have been built, using sound, light, or other things to set off the flash. I'm assuming you don't have a degree in electrical engineering and want to try something similar.

For some types of phenomena, you may be able to trigger the flash manually, simply by pressing the Open Flash button on your electronic flash. If the movement is something that just happens to be very fast, but is consistent in its motion, you can trigger the flash at any time. Say you wanted to freeze the blades of an electric fan, or stop the wings of a hummingbird; it would be fairly simple to do. Just wait until the fan or hummingbird is positioned in front of your camera lens, and trigger the flash manually. Of course, convincing a hummingbird to hover just where you want it to is about as difficult as finding a unicorn, so your subject matter is likely to be something else.

More frequently, you'll want the flash to go off in synchronization with some other event. If you're inventive, you can come up with a solution. I'll give you some hints. Electronic flash units are triggered by closing a circuit. Usually that circuit is inside your digital camera. In the case of slave units, the circuit can be closed by a sensing mechanism that detects light (from another flash) or a radio signal. In any case, a switch is closed and the flash goes off. You can create the switch yourself.

Understand that the high voltage of the flash itself is separated from the electronic circuit that triggers that voltage, so you won't be in any danger of electrocuting yourself, as long as you don't open your flash unit and start fooling around inside. The standard maximum triggering voltage for electronic flash is 24V, although many flash units use a lower voltage, and some digital cameras are able to handle only those lower voltages (which is why some cameras can't use just any flashgun).

All you need to do is build a switch that can be activated by the event you want to use to trigger the flash. If you have a flash unit that has a detachable cord, it's likely that the cord is a standard one that can be purchased at a camera store. That's good, because I'm going to suggest you cut off the end of the cord to gain access to the two wires inside. Separate the wires and connect them to two pieces of metal (even aluminum foil works). Then, arrange the metal terminals so that the event you want to photograph causes them to come into contact, completing the circuit, and triggering your flash at the right instant.

For example, you could tape the two terminals to the outside of a light bulb, slightly separated. Strike the bulb at the point of the terminals with a hammer, and just as the hammer breaks the bulb, the two contacts are forced together triggering the flash. You can place your switch under an object, so another object striking it makes the contact. Some experimenters have shot a bullet through their makeshift switch so the force of the impact closes the circuit. (I can't recommend experimenting with bullets; the experiment might work just as well with a paint gun or ping-pong gun.) I'll leave the design and construction of your switch up to you. Would a squirt-gun work? Can you build a mercury switch so when an object is tilted suddenly the flash is triggered?

There are dozens of different ways to set off your flash. This can be an interesting individual project, indeed. I hope you have fun with it.