High speed photography has changed the world of biomechanics. With the capabilities of today’s high-tech cameras, it’s possible to view recorded action as never before. Researchers can record their experiments and then play them back frame by frame for an unequaled observation and analysis opportunity. This is only possible with the highest quality cameras. To choose the best camera, you must first understand the importance of shutter speed and frame rate, and how they’ll affect the resulting images.
Shutter speed
In still life cameras, the shutter works like a door that separates the camera’s lens from the film. As a photo is being taken, this door opens to allow light to reach the film. How quickly the door opens and closes varies and this variation is denoted by the shutter speed, measured in fractions of a second.
Shutter speeds can range from one full second to 1/1000th of a second as measured. An ultrahigh-speed camera has the capacity to limit exposure times to less than 50 microseconds. The faster the speed, the shorter amount of time the film is exposed to incoming light and thus the less light is able to reach the film. In other words, a shutter speed of 1/100th of a second indicates a shutter which is open for 1/100th of a second. A camera with a shutter speed of 1/500th of a second would be faster, exposing the film to light for only 1/500th of a second. If you’ve ever tried to capture an image of a moving object and had it turn out blurry, more likely than not a too-slow shutter speed was to blame.
For video cameras, the shutter works a bit differently. The shutter will open and close once during each frame of the video. A video camera with a shutter set to 1/100th of a second will result in each frame being exposed for 1/100th of a second. This is not the same as frame rate, as we’ll discuss next.
Frame rate
Frame rate applies only to motion cameras. It is the number of frames, or individual images, displayed in each second of the video. Hence, frame rate is measured in frames per second (fps). A 1000 fps camera takes 1000 still images per second.
To create a video, this sequence of still images is played in rapid succession. Cameras whose frame rate is lower – – i.e. they have a smaller frames per second measure – – will capture fewer still images in each second. The result is a longer jump between images and a more choppy video.
A high frame rate camera also translate into higher pixels because there are now more images displayed per second. More pixels, mean sharper images; thus using a higher fps camera can result in a twofold sharper image. Using a 1000 fps camera will provide you with far sharper video and images than a 500 fps camera can.
A standard video camera typically has a frame rate of 18 fps. A specialized slow motion camera, on the other hand, can reach thousands of frames per second. Depending on the optical technology used, a super slow motion camera can achieve a frame rate of over 1 million frames per second.
Why shutter speed and frame rate matters
With a Phantom slow motion camera such as the 1000 fps camera, researchers can view experiments in incredible detail. By increasing the frame rate, you are essentially dividing time into smaller and smaller intervals. It’s then possible to slow playback and analyze the motion in greater detail. Consider, for instance, what happens when you play back a video taken at 3000 frames per second on a standard projector with a speed of 16 frames per second. The result is a recorded action that can be viewed at nearly 1/200 of its true speed.
The frames per second you need will depend on the environment in which you’re conducting your research. In industrial products and production, a frame rate of several thousands of frames per second is usually more than adequate for analysis and observation. Whether you use a 1000 fps camera or a still life camera with a shutter speed of 1/10000, you’ll be astounded at how much clearer your results become.
