High-speed cameras capture critical video data to facilitate the detailed analysis of projectile flights and impacts, explosions, missile launches, combustion processes, engine performance, material strength, flow/particle movement and more. There are many factors to consider when purchasing a high-speed camera. The most important of these are described below.

Frame Rate

The first and most obvious consideration in the purchase of a high-speed camera is frame rate. How many frames per second (fps) are required to capture sufficient video detail to allow the analysis of a high-speed event? Most high-speed cameras provide the ability to run at increasingly higher frame rates as the pixel resolution is reduced.

Light Sensitivity

In certain applications light sensitivity is the single most critical consideration. Light sensitivity impacts the quality of high-speed images because without it the images will be dark and difficult, if not impossible, to analyze. Light sensitivity is typically presented as an ISO value. The higher the ISO value, the more sensitive a camera should be. There are standards – such as ISO 12232 Ssat – that define how to measure light sensitivity, but many high-speed camera vendors do not adhere to the standards when they measure the ISO values of their cameras. Some vendors publish ISO values but do not specify which ISO standard the values conform to. Without such information the ISO values are meaningless.

Minimum Exposure Time

Some very fast high-speed events require extremely short exposure times – sometimes even less than 1 microsecond – to stop the motion of those events. A camera’s ability to achieve a sub-microsecond exposure is dependent on two things. First, the camera’s sensor must be technically capable of performing such a short exposure. Second, the camera’s sensor must be sensitive enough that when it does utilize a sub-microsecond exposure it can capture enough photons of light to generate video that is of sufficient quality for analysis.

Resolution

High-speed cameras are available in a variety of resolutions. Most often, the resolutions are between 1-megapixel and 4-megapixel. Higher resolutions are important when the field of view of the camera is large, or when a very small spatial resolution is required because there are a lot of fine details in the high-speed event that need to be studied. It is important to understand that the higher the resolution of the camera, the lower the maximum frame rate will be. With a 4-megapixel camera there are 4x more pixels to process than with a 1-megapixel camera. Therefore, it is not possible to achieve the same frame rates with a higher resolution camera as with a lower resolution camera. In addition, higher resolution cameras are typically less sensitive than lower resolution cameras because their sensors have smaller pixels.

Bit Depth

Bit depth is an important consideration as it impacts image quality and the ability to apply image processing to the images to enhance their usability. Most high-speed cameras capture image data that is either 8-bit, 10-bit or 12-bit. The higher the bit depth, the greater the amount of information that is captured by the camera.

Internal Memory

The amount of internal memory is an important issue for consideration when purchasing a high-speed camera, as a high-end, high-speed camera can generate a huge amount of data in a very short time. For instance, a high-end camera can generate 128GB of 12-bit image data in just under 4.5 seconds when run at 20,000fps at 1-megapixel resolution. Because no streaming mechanism exists to allow this amount of data to be transferred to a PC or external storage device in real time, high-speed cameras have internal memory to which the image data is initially captured. After the recording is completed, the image data can then be offloaded to a more permanent location.

Data Offload

After the high-speed event has been captured by a camera, the video data must be transferred from the internal memory on the camera to a more permanent location for storage and analysis. Most camera suppliers have chosen to implement some form of Ethernet to enable the transfer of the data from the camera. Because the recorded data can be tens of gigabits or larger in volume, the data transfer over Ethernet can be a bottleneck in getting the data out of the camera.

As an alternative to Ethernet, some cameras can download images at very high data rates to a removable nonvolatile memory source such as a high capacity removable SSD. Recorded data can then be directly accessed from the SSD while it is coupled to the camera, or the drive may be removed from the camera and inserted into a docking station for image transfer to a PC.

Sealed Camera Body

Certain testing environments contain large quantities of airborne dust and other corrosive particles. Some camera suppliers have implemented a sealed body design that prevents such contaminants from being ingested within the internal camera body where they can adhere to and damage sensitive electronics.

Summary

Military testing environments can be especially challenging for high-speed cameras. Frame rate and light sensitivity are typically the most important factors to consider when purchasing high-speed cameras, but as discussed above, there are other things one should think about such as minimum exposure time, data offload speeds, and a camera body design that protects sensitive electronics from contamination by airborne particles.

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