Catching the Falling Drop


Posted on Feb 6, 2014

The goal is to take photos of some fairly quick process (well, at least too quick for the human eye) at exactly specified times with sub-millisecond accuracy. Of couse, with expensive special equipment at hand (such as a high speed camera), this is a trivial joke, but I wanted to do it in my room with the stuff and `toys` I have laying around as w


Catching the Falling Drop
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ell as a normal digital camera (Minolta) and an ordinary photo flash. The camera has a much too long delay from pressing the button until the exposure actually begins so one has no chance to catch the drop this way. Furthermore, the minimum expose time is 1ms but it would be better to further reduce it in order to get sharper images. So, the basic idea is to make the room dark, open the camera`s shutter, let the drop fall down, fire the photo flash at the correct time and close the shutter again. To provide me with drops in roughly constant intervals, I used a standard pipett with some toilet paper inside to drastically limit the liquid flux. The method worked surprisingly reliable. Checking out my electronics stuff, I found a transmission light barrier extracted from a very old floppy drive which was just wide enough to get the drop though (after having adjusted the drop source position). On the left you can see an image of the light barrier together with a milk drop which just went through it. Especially note that the drop is completely spherical and has no special "drop-like" shape. Still needed, however, was the delay trigger to fire the flash light some specified time after the drop crosses the light barrier. For the height I was using, the base delay until the drop crashes was about 1/4s to 1/2s (250-500ms). To see the different stages of the crash, some precisely defined amount of time in the order of single...




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