Video Analysis with High-Speed Cameras

Video analysis of a golf swing

Casio recently developed a set of high-speed cameras. These cameras are actually still digital cameras, but they have the ability to capture high-speed video. The capture rates vary from 210 frames per second (fps) to 1200 fps. The price range is from $300 to $1000 per camera.

These cameras open exciting opportunities to explore science that is difficult to see at normal speed. Here are a couple of examples: Teachers want to collect motion data from fast-moving objects, such as the speed of a baseball as it leaves the pitcher's hand, or the speed of a golf ball after being struck by a club. It would be natural to assume that a Motion Detector could help answers these questions, but these objects move too quickly for the Motion Detector; however, video analysis of these fast-moving objects offers a great solution. We measured the speed of a golf club and the speed of the golf ball after impact using a Casio EX-FH20. The figure above shows a frame from the video analysis, and the graph shows velocities of the club head and ball.

There is one, easily corrected, technical challenge in getting this data. During video analysis, Logger Pro gets the times associated with each frame from the time stamp that the camera puts on each movie frame. High-speed cameras are designed to replay the movies in slow motion, so instead of using the actual frame rate, for example 1000 fps, they use a 30 fps rate. Logger Pro does not have the correct frame rate available. All you have to do is create a calculated column based on the Time column that was created during the video analysis. Choose New Calculated Column from the Data menu. Give the column a name, e.g., Time Correct, and then in the Equation field enter the conversion, e.g., "Time"*30/1000.

Logger Pro also calculates velocities. These are derivatives of the x and y positions using the 30 fps time stamp from the movie. You will have to change those definitions to use the corrected time. All you do is choose Column Options from the Data menu and then choose one of the velocity columns, e.g., X Velocity. In the Equation field, replace “Time” with “Time Correct.” If you are also measuring the y velocity, make that correction too.

Download the video and Logger Pro experiment file »

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