How High-Speed Photography Functions

Photography captures the essence of a fleeting moment. Life can often rush by in a blur, and it is the beauty of photography that allows us to freeze these moments and relive them later.

But what about those moments that slip by too quickly for us to capture? Moments that we can't photograph with a standard point-and-shoot camera or even perceive with the naked eye? If you tried to photograph a bullet speeding past, the result would likely be just the background, with no sign of the bullet. Similarly, if you tried using your digital camera to snap a hummingbird's wings in mid-flight, the bird's wings would appear as a large, blurry triangle in your photo.

However, people have successfully photographed a bullet piercing through an apple, with the core beginning to explode, and the bullet visible as clearly as if it were right in front of you. Nature magazines often feature images of birds frozen mid-flight, where you can count the feathers on their wings. There are countless pictures of water balloons bursting, wine glasses shattering, and water droplets just about to touch the surface—things that are invisible to the naked eye. How do they manage this?

High-speed photography captures fast-moving subjects, documenting events that are usually invisible to the human eye. Scientists use these photographs to analyze physical movements, studying phenomena such as surface tension and gravitational effects. The military employs high-speed images to assess missile and rocket accuracy, and it even allows us to observe what happens at the heart of nuclear explosions. Sports photographers use high-speed techniques to shoot fast-paced events like NASCAR, cycling, and horse racing. High-speed photography also finds a place in art, with galleries and magazines showcasing breathtaking high-speed photos.

Capturing high-speed action might reveal sights never seen before. So, how does one photograph a speeding bullet? What kind of camera is necessary for high-speed shots? Is it a simple task or does it demand practice and expensive equipment? To uncover how people capture the unseen on film, keep reading.

Basics of High-Speed Photography

To grasp the core principles of high-speed photography, it's essential to first understand the fundamentals of photography and how a camera operates. Specifically, it's valuable to learn how manual cameras function, as opposed to modern automatic and digital models. While automatic and digital cameras can capture high-speed subjects, when it comes to high-speed photography, the more manual the camera, the better the results. Therefore, we will focus on manual single-lens reflex (SLR) cameras and the basic photography principles.

One of the most crucial components of a camera is the lens. A lens is a simple, curved piece of glass that bends and redirects incoming light to create a real image, which is an accurate representation of the scene before the camera. The light passing through the lens is essentially 'painted' onto the film inside the camera. It’s no surprise that the term 'photography' originates from Greek, meaning 'drawing with light.'

You can't simply aim a lens at a subject and expect the picture to turn out well. Two key factors determine how the film is exposed to light:

The first factor, the amount of light that reaches the film, is controlled by the camera's aperture, which is a circular opening that can expand or contract. The aperture functions much like the iris of your eye — when more light is needed, the circle widens; when less light is required, the circle tightens. A set of numbers on the aperture control of a camera, known as f-stops, indicate the size of the aperture. The f-stop is inversely related to the aperture size: a higher f-stop number corresponds to a smaller opening. For instance, an f-stop of f/11 allows less light in than an f-stop of f/8.

The component that works alongside the aperture to control the second factor — how long the film is exposed to light — is called the shutter. The shutter is essentially a curtain that opens and closes to let light hit the film. More specifically, the shutter speed, or the speed at which the shutter opens and closes, plays a key role in the exposure. Shutter speeds are typically expressed in fractions of a second and can range from a full second down to 1/1000th of a second. The longer the shutter stays open, the more light reaches the film.

So how do these factors come into play in high-speed photography? To understand how high-speed photographers capture such rapid movements on film, continue reading on the next page.

High-Speed Photography: Flash Duration, Shutter Speeds, and Exposure

To grasp the concept of high-speed photography, we also need to consider its counterpart: long or extended exposure photography. This method involves keeping the film exposed for longer periods — anywhere from an eighth of a second to several minutes.

Busy urban traffic scenes during dusk, dawn, and nighttime are typically featured in extended exposure photos. In these images, car headlights appear not as tiny dots of light, but as long streaks that weave across the frame, blending together. This happens because the light from a car's headlights effectively paints across the photo frame, remaining exposed on the film for an extended period.

If you attempted to capture something like a bullet with the same long exposure technique, you’d barely notice a faint streak across the image. This is because a bullet travels across the camera lens in a fraction of a second, allowing too much light to expose its entire path, from one side of the frame to the other.

The key to high-speed photography lies in how quickly the film is exposed to light. For this reason, high-speed photographers rely heavily on flash units, utilizing extremely brief flash durations — the shorter the flash, the better. Many high-speed shots are taken in total darkness. In this scenario, the camera's shutter remains open while the shot is taken; without light, the film remains unexposed. Once the object moves through the frame, the flash unit releases a quick burst of light, capturing that instant on the film. Flash durations can be as short as 30 microseconds, or 0.00003 seconds.

Photographers capturing outdoor nature scenes or sports events, where complete darkness isn't possible, rely on incredibly fast shutter speeds. While standard photography in daylight might work with shutter speeds around 1/125th of a second, high-speed photography requires much faster speeds — as quick as 1/8000th of a second.

How does a photographer align all these variables to achieve such sharp images? To explore topics like detection, synchronization, and other crucial aspects of high-speed photography, continue reading on the next page.

High-speed Photography: Detection, Synchronization and Imaging

To capture the perfect, sharp image of a moment frozen in time, three key elements must align to create a high-speed photograph:

As the actions being recorded happen too quickly for the human eye to detect, fast-moving and sometimes unpredictable objects must be detected remotely. Essentially, the subject of the shot alerts the camera on when to take the picture. By connecting various triggers, such as sound, vibration, physical contact, or light interruption, electronically to a flash unit, the high-speed object can notify the flash almost instantly when to emit a burst of light.

In this instance, it was the sound of the gunshot, not the photographer, that activated the flash.

Sound triggers are frequently used in high-speed photography, mainly due to their simplicity and ease of use. A typical sound trigger setup consists of three components: the microphone, the amplifier, and a silicon-controlled rectifier (SCR). Rather than using a regular microphone, photographers may use piezoelectric film, which is pressure-sensitive and reacts to sharp sounds, such as a balloon popping, glass breaking, or a hand clap. The sound detected by the piezoelectric film is amplified by the amplifier, sending an electrical current to the SCR. The SCR, connected to the flash unit via a cathode and anode, acts as a switch for the flash by shorting it. If the photograph is taken in total darkness, the camera's shutter can remain open without exposing the film until the flash triggers the shot.

When a photographer is shooting outdoors and depending on fast shutter speeds, the timing of the shot becomes crucial. The camera must be synchronized to capture the exact moment an object crosses the frame. This requires understanding the delay between the object's movement and the time needed for the camera to take the photograph.

Imaging refers to the process by which light paints an image onto the film. The type of film a photographer uses can sometimes influence the result of a high-speed photograph. In high-speed photography, film speed — the film's sensitivity to light — plays a significant role. Film speed is commonly measured in ISO (International Organization for Standardization), and a lower ISO means it takes longer for light to expose the film. For instance, a film with an ISO rating of 800 is faster and more sensitive than one with an ISO of 100. Since high-speed photographers typically work with low light, they tend to use faster film speeds to compensate for the brief flashes of light used.

Despite meticulous planning, high-speed photographers often rely on luck just as much as they do on preparation to capture the perfect shot. Snapping a well-defined water droplet, for example, could take over a hundred shots over the course of several hours. However, for many, the allure of freezing time and revealing something never seen before makes the effort worthwhile.

For more information on the science of photography, refer to the next page.