|
Activity
6. Photographing the smash of a tennis ball or racquetball
Equipment needed:
- Vivitar 283 flash unit
- 4 AA batteries or SB-4 AC adapter
- Flash-to-trigger cord
- Flash clamp
- Piezoelectric sound trigger
- SLR camera and film
- Tripod
- Penlight
- Tennis ball or racquetball and racket
- Large cloth sheet or blanket
The setup for this photograph is more involved than that of a
balloon burst but can easily be done in a small room.1
A typical arrangement is shown in the overhead view below. The sound
trigger should be placed as close as possible to the location where
the collision of the ball and racket will occur. If one were doing a
forehand shot, for example, the sound trigger could be placed on a
stool or box about a foot below the spot where the racket met the
ball. Of course, sufficient room would have to be left around the
person wielding the racket to allow freedom of movement.
The background can be a problem if you plan to include the person
swinging the racket in the photo. You may want to dispense with a
hung background and simply make sure the subject is far from a wall
and that distracting objects are removed from the background.
The ball can easily be stopped without rebound in a sheet
or blanket hung from the ceiling or other support. Let the blanket
hang freely. If it's stretched tightly, it will reflect rather
than stop the ball. The position selected for the camera
depends on whether one wants a side view, front view, or back view
of the ball. The flash position should be selected so as to avoid
throwing unwanted shadows across the ball.
| Safety considerations:
Be sure that everyone stands away from the possible path of
the ball. The potential for eye damage from an errant
ball may be increased since the room will be dark, and one
may not be able to see well enough to dodge the ball.
It's a good idea not to darken the room completely.
Cracking a door or a window shade won't let in enough light
to affect your photos, but it will allow you to see what
you're doing. |
Before attempting photographs, have the person who swings the
racket take some practice swings with the room lights on. Then
repeat with the lights off. If the room is too dark, a penlight can
be used to illuminate the ball during the swing. The flash will
probably be bright enough in comparison so that the light from
the penlight is not noticeable.
Like always, prepare your data page before taking the first
photograph. Then evaluate your results afterward and record
your conclusions.
 |
The photograph to the left shows the position
of the sound trigger relative to collision site. The
trigger was taped to a tripod. This allowed the
height of the trigger to be adjusted easily. Note that
the flash is positioned to the camera's right, as evidenced by
the shadows. Had the flash been placed to the left, the
ball would have been in shadow. |
| Tip: Using
a piezoelectric trigger for these collisions is
marginal. The thud that the collision of the ball and
racket makes doesn't generate much of the high-frequency
content for which this trigger is most sensitive. Here
are some ways to increase your chances for success: i)
adjust the trigger sensitivity as high as possible, ii)
place the trigger as close the site of the collision as
possible, iii) hit the ball hard. If these don't work,
it may be time for a sound trigger with a wider frequency
response. Go
here to find out how to make an extremely sensitive
sound trigger from a tape recorder. |
Notes
1. An alternative to hitting the ball with a racket is
simply is to throw the ball down on the floor. This is
especially effective with a racquetball. The sound trigger is
placed on the floor and can be moved to different positions to get
different time delays. Before trying this, though, make sure
that anything on the ceiling that the rebounding ball might hit
isn't breakable. And when throwing the ball, be sure to be out
of the way of the rebound.
|
