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Method and Setup

Equipment

    CAMERA

    FLASH

    TRIGGER

    RIFLE

    MISCELLANEOUS

 

Perspective View of Setup

 

Top View of Setup

*The zoom on our original camera did not function properly, therefore, during our last session we used another, functioning, CoolPix 990 camera.

**We had four flashes and triggers in our original setup, however, for the majority of our project we only used one flash due to time restrictions.

 

Setup

    Our setup, as shown above, was arranged with the subject (the bulbs hanging from the stand) ~1m from our black backdrop.  This was done so as to prevent glare from the background, which can occur if the subject and/or flash is too close.  Our camera's zoom was not functioning properly, therefore we placed it at 0.8m form the subject to get it as close as possible without risking damage from bulb shards.  For further protection, we covered the camera's lens with a glass shield.  The flash unit was stationed near the camera, at the same distance from the subject.  Our sound trigger's placement varied, but for the most part it was about 3.5m from both the gun and the subject.  This was done so that the BB/pellet was where we wanted it to be in the picture.  Depending on the amount of times the gun was pumped, which altered the speed of the BB/pellet, we adjusted the distance of the sound trigger.  Finally, the gun was placed on the opposite side of the subject from the BB trap, about 2m from the subject.

    For several of our pictures we used multiple flash units with four different color filters.  We did this in order to get a progression effect of the shattering bulbs.  The units were placed on the same flash mount as the single flash unit referred to earlier and the appropriate sound triggers were placed increasingly further from the gun in order to obtain varying time delays.

 

Triggering, Timing, and Imaging

    We used the sound made by the firing of the gun to trigger our flash.  Ideally, we could have used the sound created when the bulbs shattered, which would involve placing the sound triggers a good deal closer to the bulbs.  However, this was not feasible with the amount of time we had due to the fact that preventing the flashes from being triggered at the initial firing, or coming up with an alternative solution, would be fairly difficult.

    Timing was both one of the most important and one of the most challenging parts of our project.  Our goal for timing was to have the flash go off when not only the bulbs were shattering, but also when the BB/pellet was still in the frame.  This was accomplished by placing the sound trigger a good distance away from the gun (~3.5m), which would allow the sound to trigger the flash at about the same time as the bulb was breaking the bulbs.  It required some trial and error, increasing and decreasing of the distance of the sound trigger, but we were eventually able to obtain several acceptable images.

    Our imaging methods were nothing out of the ordinary for high-speed imaging, but those methods are themselves not the usual way to capture images.  First of all, because the phenomenon which we were photographing was so fast, it wasn't possible, or at least practical, to attempt to freeze the action by using a fast shutter speed (usually 1/1,000th of a second is the fastest shutter speed possible).  Instead, it was necessary to use a flash, which can have a duration as short as 1/30,000th of a second, to illuminate the subject for one moment.  Meanwhile, we set the camera's shutter to the "bulb" setting, which means that the camera's shutter stayed open as long as the button was depressed.  However, the longer the shutter stays open on a digital camera, the more thermal noise is created on the image.  For this reason, it was important to keep the shutter open for as short a duration as possible, releasing the button as soon as the flash had been triggered.  Of course, these methods required a dark room, since otherwise the film would be severely over-exposed when using the bulb setting.  The ISO, or film speed, used was 400.  It was also necessary to set the camera to manual focus mode, since if it were left on automatic focus, the camera would attempt to focus once the lights were turned out. resulting in an out-of-focus image.  The aperture we used was selected for both adequate depth of field and image exposure given the setting of the resistors we were using.

 

Experimental Method  

    Once we had all our equipment, we began by adjusting the sensitivity on our sound triggers and also getting the desired  time delay to capture the bullet in our picture.  We had to adjust the gun's aim and the height at which the bulbs hung to ensure that both bulbs were shot.  We did this by hanging a sheet of paper from our stand and checking where the bullet left a hole.  We started by shooting only one bulb.  Before we turned out the lights to take the picture, we set the right aperture, focus, and  shutter speed on our camera.  Also, we loaded the rifle and pumped it initially ten times, but later decreased our number of pumps to about four times.  We also switched from using BBs to pellets.  These changes were made so that the bulbs would shatter more completely.  Now that we had everything set up, we made sure everyone was wearing their goggles and was in a safe position.  We then turned off the lights, opened the shutter of the camera, and shot the rifle.  The sound of the rifle set off the flash, thus capturing the high speed even of the bullet shattering the bulbs.  After each picture we turned the lights back on, analyzed our image and checked what needed to be improved for our next picture.  We took some pictures with one bulb, then started using two bulbs hanging in a row.

 

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