Whence comes the feeling that between any two instants there are others?

The force of a photograph is that it keeps open to scrutiny instants which the normal flow of time immediately replaces. This freezing of time—the insolent, poignant stasis of each photograph—has produced new and more inclusive canons of beauty.*

We take for granted our modern appreciation of the hidden reality of the frozen moment, but the perception of the moment has not always been available to us. That we know (and feel we know intuitively) the look of a bird's wings in flight or a bolt of lightning mid-strike is largely a result of photography. We are so sure of our knowledge of the instant moments that people sometimes find it hard to believe that Leland Stanford had to hire Eadweard Muybridge to prove a horse's hooves all left the ground during a gallop—we have trouble imagining that there was ever a time when we didn't know this and that you can't tell just by looking. Exploring the hidden instant is almost as old as photography itself. Ernst Mach was making shadowgraphs of flying bullets as early as 1838. A hundred years later Harold "Doc" Edgerton elevated it to an art. Despite our certainty that we know the world in front of us, photography still has the power to check our confidence, like this Discovery Channel "Time Warp" of a dog drinking. I've watched a lot of drinking dogs, but I had it all backwards.

Today we're going to look at one of the tiny little marvels of fluid dynamics that happen in front of us everyday in those invisible fissures of time that elude our vision. What follows is one way to shoot water drop photos—not exactly the drop but rather the rebound after a drop has hit the water. This is a pretty common subject so we'll try to distinguish ourselves by lighting them as well as we can with a single light. Like the smoke photographs from the previous recipe, these are relatively easy and require minimal gear, but the water drop photo presents a few more technical challenges: freezing the moment, focus, and lighting.

Freezing the moment is the easiest part. Most small hotshoe-mounted flashes have incredibly short flash durations—this is one area where they routinely outperform all but the most expensive studio lights. According to Nikon's specs, the SB900 I'm using here has a flash duration of 1/10000 second at 1/16th power. At 1/128th power is is blazing: 1/38500 second. We won't need a lot of light; as long the ambient light is low enough not to affect the exposure, this is more than fast enough to freeze our splashes.

Focus and lighting are a little trickier. Have a look at the setup:

Since the drops are quite small, I'm using a macro lens and focusing rather close. This leaves precious little depth of field and even with a small aperture there is no room for focusing error if you want sharp shots. But there's nothing to focus on until the drop is flying by and it moves way to fast to focus on. The trick is to make sure you can make the splash happen in the same spot every time. The camera is stationary on a tripod and the water drops are coming from a syringe clamped to a heavy boom extending above the middle of the glass. I attached a plumb-bob made of thread and a bolt to the end of the syringe and focused on the exact spot where it hit the water in the glass. So long as you don't move anything, the shots will be in focus.

Lighting is the hardest part. Here's the thing to remember about photographing anything transparent, whether it's glassware, gems or tiny drops of water: You aren't really photographing the drop of water but rather the effect it has on light. Water has a refraction index of 1.33 which is greater than air. This means that each time a ray of light passes the boundary between air and water it gets bent (see Snell's Law for details). The water drop acts like a lens presenting a wider angle of view. You can use this knowledge to define the edge of the water drop preventing it from disappearing into the background. This is what the flags do. They are black, and along with the unlit area to the right and left of the sweep they are visible only through the lens of the water droplet. By making the areas between the two angles of view dark you create the nice magic-marker edge in the water drops. The flags also prevent specular highlights from reflecting off the water. The only light in the image is the reflection of the background which means you won't get any specular hot spots like you would if you tried to light the water directly. The color is coming from blue food color added to the water.

Once it is all set up the only trick left is timing the exposure to the exact moment of the drop. After about 10 tries I got the timing down and was able to do it without resorting to any fancy triggers. One hand on the camera and one on the syringe. Drop-click, drop-click. The rest is just the beautiful play of surface tension and gravity.