Equipment:
Sony Digital Still Camera- DKC-FP3
Apple II+ Computer with interface and Intervalometer II program4
Light Box
Milk Drop Station
Photogate
4x4, c-clamps, and tripod screw to secure camera
Clear plastic container to hold water
One Vivitar 283 flash
Technique:
To study the splash of a water drop, we started taking pictures before the drop hit the water and then every 10 milliseconds after until the spout reached its pinnacle. To accomplish our goal we overcame many challenges. The obstacles in our project were the lighting of the subject, focus, and timing.
Water is very hard to light and capture in a photograph because of its transparency and its ability to refract light. We tried to use a stroboscope to produce a flash at a given time interval and light ou subject. This was a good tool to help us study the formation of the drop, however the light emitted by the stroboscope was not bright enough to light the subject from the side. Finally we decided to light the subject from beneath. We accomplished this task by using an apparatus designed by a former student. This device was made from an old overhead projector ( see appendix for drawing ). The device allowed us to use a Vivitar 283 flash to illuminate the small container of water and the drop from beneath. This lighting worked well.
The next problem we faced was focus. Because water is clear and it refracts light, the subject was very hard to focus on at such a close distance. We had several photo shoots before we finally got the focus clear. Part of the problem was the stability of the camera base. We were able to use a 4x4 and a tripod mounting screw to secure our camera and minimize movement. Because the drop was moving we had to focus on another object that was where the drop would be. We put a pencil in the water and focused until we could read the writing on it.
Timing was the biggest problem. When the water dripped into the small container, it raised the water level, which changed the distance between the photogate and the water, therefore changing the stage of the splash captured by the flash at a constant time interval. In the end we were able to shoot the pictures quick enough that the height of the water did not change significantly.
The procedure began by connecting the Apple II+ to the photogate and the flash. Then we filled the small plastic container with water to a certain level marked on the side. Then we put water in the dropper. Next we had to experiment to find when the drop hit the water and how long afterwards the spout reached its peak. Last was the stage for taking pictures. We mounted the camera, zoomed and focused on a pencil in the water, and then it was time to take photographs. The lights were turned off and the drip was started. We took several pictures at each time using a shutter speed of one second to ensure that we got a picture for that time interval. Then we examined our pictures.