Equipment

• Nikon Coolpix 990
• Vivitar 283 flashes
• Toshiba T1600
• Input & output interfaces
• Contact trigger

Apparatus and Method

We attempted to take pictures of multiple balls and then to compare various attributes of each ball. We looked at how long each ball took to collide and rebound and at how much it compressed. We tried to use three different balls: the green and orange "goooz" ball, the blue and green globe, and a hard rubber ball.  We weren't able to photograph the (very short) collision of the hard rubber ball and we ran out of time before we were able to photograph the globe.

We used a simple contact trigger to set off our flashes.  Most of our pictures were taken with a single, uncolored flash; we took photos every 2ms in a collision (actually multiple collisions set up identically, and we changed the delay every time). We also used multiple-flash photos with no delay and an interval between flashes to show the ball's distortion.  We used a computerized intervalometer to time our flashes.  In order to take photographs, we used a two-second shutter speed.  One partner would open the shutter, and the other would drop the ball from a marked height.  The two-second shutter speed allowed enough time for the ball to fall and the flashes to go off.

In order to make our experiment set-up mobile we constructed our apparatus on a television cart with wheels. The cart had three shelves. We put the computer intervalometer along with the input output interfaces on the top shelf of the cart so that one of us could stand at the computer during the experiment.  The intervalometer allowed us to capture more than one image of a bouncing ball by setting off our four Vivitar 283 flashes at an interval of our choice.

The Vivitar flashes were plugged into the output interface, which was connected to the intervalometer. All of the flashes were placed on the bottom shelf of our cart all 0.3 meters from the collision. We had different colored filters on each flash so that we could tell what order the images appeared in. The four flashes sequenced: red, green, blue, then yellow. Where the flashes overlap the object would appear white, if it was white to begin with.

We also had a contact trigger plugged into the input box interface of the intervalometer. The trigger consisted of two metal plates which were slightly separated; when a ball was dropped onto the trigger, the two plates came into contact and the circuit was completed. The contact trigger was the initial input required for the intervalometer. Once the trigger was tripped the first flash would go off after a set delay time followed by the rest of the flashes in sequence.

In order to get this contact trigger at eye level with our camera, which is on a “table top” tripod taped to the floor about .28 m from the subject, we stacked books under it. It is important that the subject be at eye level with the camera so that the compression of the ball can be accurately measured.