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How Ultra-High Speed Cameras Work
Have you ever watched perfectly clear footage of an object moving at ridiculously fast speeds and wondered how they captured it? We’re talking about the flight of a tank shell or the blossoming of a nuclear weapons test. You may think that regular cameras would be unable to move at such speeds, and you’d be right. There are many powerful technologies used in such capture, but also some interesting photography principles applied. In this post, we’ll take a look at how ultra-high speed cameras work and give some examples of how the technology has progressed.
Smoke and Mirrors
Projectiles in flight are usually impossible to track with a regular camera. Although much of the footage you see of such ballistae gives the impression that the camera is tracking the movement, this isn’t the case. Tanks fire shells at around 1500 meters per second, making it impossible for a panning shot to capture them. Instead, a mirror system is implemented.
A computer-controlled mirror, capable of rotating at incredibly high speeds is used. It is placed in the line of sight of a high-speed camera, and the mirror matches the speed of the object being followed. This method gives the capability of capturing the flight of an object for around 100 meters. Systems like the Tracker2 Flight Follower System can be used to track projectiles that accelerate either linearly or non-linearly.
An Explosive History
Some of the first high-speed camera systems used mirrors to track movement, and in recent times some of the fastest cameras have also use this method. Today, some of these systems can capture footage at up to 25 million frames per second. However, the technology as we know it today has its origins in the development of the first atomic bomb.
Scientists required cameras that could accurately capture the first few microseconds of a blast. To determine whether the bomb’s core compressed correctly, they needed to observe how in-sync the high-explosive lenses responsible for the detonation were. At the time, the fastest cameras were only capable of capturing footage at 10,000 frames per second.
After various improvements implementing rotating mirror systems, scientists devised the Rapatronic camera. This camera used a magneto-optic shutter, capable of a shutter time of a staggering 10 nanoseconds. The only downside of this system was that it could only take one image at a time. To successfully capture the bomb detonation, the engineers used a series of cameras and compiled the results.
Experts working on British nuclear tests in the 50s devised the high-speed C4 camera. This also used a colossal rotating mirror system that captured footage at 7 million frames per second. The rotating element reached speeds of up to 20,000 RPM. Today, modern high-speed cameras use a similar system. The Cordin Model 510, for example, uses a helium gas-driven turbine mirror to capture footage at up to 25 million frames per second. At this speed, the mirror rotates at 1.2 million RPM.