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Hack 46 Second-Curtain Flash for Cool Effects

One of the most magical of all camera tricks,
second-curtain flash lets you show a trail of motion behind an object
that is frozen in mid flight.

Typically, you use a camera flash to add light when
there's not enough ambient illumination for a
well-exposed shot, or to fill in shadows for portrait subjects. In
either of these scenarios, you typically have a relatively fast
shutter speed (1/60 of a second or so) with the flash occurring at
the beginning of the exposure, otherwise known as the first
curtain. The term curtain refers to
the phases of the shutter. The first curtain occurs at the beginning
of the exposure and the second curtain
[Hack #29]
to capture some background information that would otherwise be dark
because the flash can't reach that far. Subjects
must stand still during these long exposures; otherwise,
they'll blur in the photo.

Technically, a second-curtain flash
is just a technique in which the flash fires at the end of
a long exposure rather than at the beginning of
it. So, why would you ever want to have the flash fire at the end of
the exposure? Well, it creates great opportunity for the best of both
worlds. On one hand, you get the artistic motion trail that
illustrates the movement of an object, often revealing patterns or
characteristics about the movement that we can't
otherwise perceive. On the other hand, you also get to
freeze the subject at the end of the motion. By
having the sharp representation of the object at the end of the
motion trail, rather than at the beginning or middle, you end up with
a more interesting shot that shows the history of the
subject's movements.

A classic application of second-curtain flash photography is to show
a dancer in motion or a moving object, such as a golf club or a
bouncing ball. In the example shown in Figure 4-14,
I shot a playing card flying through the air at 1/2 second at f-7.1.

Figure 4-14. Second-curtain flash

4.9.1 How to Create the Magic

You'll need a camera with a
Second Curtain flash mode or one that
accepts external flashes with this option. In this hack, I used a
Canon
Digital Rebel with a Canon Speedlite 550EX. When shopping,
you'll have to check the specs carefully, because
some great digital SLRs don't have this feature,
while a plain-Jane consumer digicam just might.

For your setup, mount your rig on a tripod, set the flash to Second
Curtain mode (it will be there somewhere in the controls), put the
camera in Manual Exposure mode, and try a beginning setting of one
second at f-5.6. It's also helpful to have a remote
release for this type of shot.

Now, pay some attention to your background, because
you'll want one that differs in tone and/or color
from the subject. Typically, these types of photos are shot with a
light object on a dark background.

Put the object in motion and trip the shutter.
You'll hear the click of the
shutter opening, but no flash...at least not yet. When the shutter
clicks again to close, the flash will fire. That's
the beauty of the second curtain. The shutter is open, capturing the
object's movement, and then the flash fires right at
the end of exposure, freezing the subject in mid flight and thereby
rendering a natural-looking composition.

You'll need to take many test shots to perfect the
composition, the lighting of the scene, and the motion of the object.
The length of the trail is determined solely by the length of the
exposure time (given that you don't have any control
over the speed of the subject). The intensity of the motion trail is
determined by the strength of the ambient light on the subject, as
well as the camera's ISO and aperture settings. The
intensity of the frozen image at the end of the exposure is
determined by the flash strength. To maintain the most control, put
the flash strength on manual control; this feature typically requires
an external flash.

If you are shooting a light object on a dark background,
the goal is to light the subject but not the background. There are a
number of things you can do to achieve this. For starters, move the
background as far away as possible. In my example, I used a large
black sheet as the background and moved the camera as far away as the
size of the sheet would permit.

Another tip is to place the ambient light source (such as a desk
lamp) and the flash off to one side and light the subject at an
angle. The goal is to place the lights so that their illumination
doesn't hit the background.

So, how do you move the flash off the camera but still retain
communication? One trick is to buy a relatively inexpensive coiled
cable that connects to the flash on one end and the hot shoe on the
other [Hack #42] .
A more expensive approach is to use a wireless flash system [Hack #43] .
A homemade approach is to aim the flash off to the side or directly
up and bounce it off a reflective surface, such as a piece of white
cardboard. Also, keep in mind that the less reflective your dark
background is, the easier it will be to control the lighting.

Choosing to tackle a shot with a dark object on a light background
will make your work harder, because you will have to light the
background but light the subject only minimally. If you have too much
ambient light, the motion trail will be blown out in the background.

If your shot involves throwing an object across the frame, keep in
mind that you probably won't get the perfect throw
on your first shot. It might take a hundred or more attempts.
That's okay; it's not like
you're burning film. In fact, many of your best
shots come from unexpected results.

If you're shooting a scene that you
can't test over and over and you
don't know how long it will take the subject to run
through the composition, you can set the camera to Bulb mode and hold
down the shutter as long as you want, which ideally should be until
just before the subject exits the end of the scene.

Keep in mind, however, that with digital SLRs the viewfinder is
blocked during these long exposures because the mirror is flipped up,
allowing light to pass through to the sensor. You can get around this
problem by looking for a reference point on the background where your
composition endsperhaps a distant tree or building. While
you're shooting, observe the scene with your eye
over the top of the camera and judge the end of the frame based on
the reference point. You don't want to ruin a good
shot by having it run off the scene, so frame a little wider and crop
on the computer later if necessary.

Try second-curtain flash with a variety of subjects. You can combine
this technique with others mentioned in this book (such as [Hack #33] )
for some truly impressive results. Let your imagination run
wild.

David Goldwasser