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Project X19: Setup and Method |
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Setup Description The “shooting range” of our project was about one foot in front of the black backdrop that was attached to the wall behind the shooting range. The shooting range consisted of the subject between a gun about one meter away and a BB trap on the other side. The entire “range” was placed on a counter in a lab room. The camera was aimed at the subject and placed directly in front of the subject about one meter away. The named subject consisted of an ice sheet held upright by a clamp that stood on multiple textbooks and mousepads to elevate the sheet to the height of the gun. The clamp in which the sheet was held was covered by a black sheet to prevent light reflection. The flash unit was aimed at the subject and situated in to the right of the camera and about one meter away from the subject. The trigger was placed two meters away from the gun, facing and directly in front of it. This distance and orientation, along with the delay, was calibrated to capture the BB as it was interacting with the subject. Triggering, Timing, and Imaging The sound of the gun firing was used to activate the sound trigger about two meters away which would in turn activate the flash after a given delay from the TCB. Our TCB allowed us to vary our timing throughout the experiment. After our initial round of trial-and-error to pinpoint the location of the BB with a given sound trigger distance and delay, we adjusted the timing very slightly only through the TCB box. This allowed us to vary the timing enough to capture both the very beginnings and the very ends of the collisions. Because the timing of a BB collision is so tight, only the .05 second range provided by the TCB box was necessary. To best capture the shattering of the ice, and in some cases the BB in the photo, the flash was set to as short a duration as possible to minimize motion blur. This was done by replacing the auto-thyristor with the variable resistor (set to minimum resistance) to shorten flash duration to about 1/30000 of a second. To do the actual imaging of the collision, the Open Shutter technique was used. The shutter speed was set to 2 or 0.5 seconds, and the gunman fired when the cameraman indicated that the shutter was open. The 2 second shutter speed was inadequate in minimizing thermal noise, so a 0.5 second shutter speed was used to capture the high-speed event. The procedure was performed in a dark room with the ISO set to 400. This was to avoid over-exposure of the photos, since a 2 or 0.5 second shutter speed would result in extremely bright photos in a well-lit room. Experimental Method: Once all equipment was acquired and all of the setup established, the gun was aligned with the ice sheet so as to produce a hole near the center of the sheet when fired. Then, the sound trigger distance and sensitivity were tested to ensure an optimum interaction between the subject and the BB fired by the gun. The maximum speed of the BB gun was around 0.75 mach when pumped ten times, so we pumped it nine times to produce very dramatic effects without being needlessly unsafe. Then, once the gunman gave the signals for the gun being loaded, aimed, and ready to fire, the light-man switched off the lights and the cameraman activated the camera, giving the signal to fire. The gun was fired, and the Open Shutter technique was used to take the photos. The photo taken was analyzed for possible changes to the camera settings for the next photo. For the first photo shoot, f-stop was set to f/6.4, the shutter speed to 2 seconds, and the ISO to 400. After evaluating the photos, the shutter speed was changed to 0.5 seconds for reduction of thermal noise in the second photo shoot. During the course of the experiment, the delay varied between 0.01 seconds and 0.05 seconds. The subject also varied; several times multiple sheets of ice aligned so that they would be hit side-on were used instead of single sheets. |
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