The TA and laboratory staff will show you how to configure and use the high-speed camera. Below are some things you will need to take into consideration when setting up. To assist you here are some short videos showing how to use the camera.

In order to collect enough data at the moment when the pinch-off occurs, you need to run the camera at a frame rate of at least 10,000 frames per second (fps). (However, 20,000 fps is even better.)

When setup to use the full resolution of the sensor, the maximum frame rate is about 1000 fps. As you reduce the resolution (thereby using fewer pixels) the maximum frame rate increases. To get an adequate frame rate you will need to make the resolution as small as possible. The question you need to answer is “How small can you go?”

Your goal is to record a high speed movie of the moment the drop pinches off. You will be making measurements of the narrowest part of the neck of the drop, so the active area of the camera sensor has to be wide enough to see the full width of the neck throughout the whole pinch-off process. You also need enough vertical pixels to record the drop as it falls, right up to the point where it pinches off. Therefore, you will need to play with different camera resolution settings as well as the height of the syringe until you are satisfied that you are recording all of the features you need to see at a sufficiently high frame rate.

A consequence of increasing the frame rate is that each frame is exposed for a shorter period of time. This results in dimmer images as frame rate increases. For this reason you need to get as much light into the camera as possible. There are two factors under your control that affect image brightness.

First is the brightness of the lamp which illuminates the drop. Note that we are back-illuminating the drop so that we actually record its shadow. To provide more uniform illumination of the drop, it is best to place a diffusing material (such as wax paper) in front of the light source. Experiment with the placement of both the diffuser and the lamp to obtain the brightest and most uniform illumination of the drop.

The second factor under you control is the aperture of the camera. Wikipedia has a nice explanation of how changing the aperture affects the image. In short, decreasing the aperture (higher f number) reduces the amount of light reaching the sensor but increases depth of focus, while increasing the aperture (smaller f number) increases the amount of light at the sensor at a cost of decreasing the depth of focus. The aperture is controlled by rotating the blue ring on the camera lens.

Filling the video frame without wasting space (thereby utilizing the full resolution of the camera) may require adjusting the position of the camera relative to the drop.