Flash is a powerful tool in imaging.
Flash allows you to bring more light to a subject and to freeze
action that is too fast for even the camera's shutter.
Whether built in to the camera, attached to the hot shoe, or
connected by wires or a wireless link, mastering flash will help
make you a better photographer.
A flash unit consists of a small xenon filled tube and the electronics to
supply the tube with a brief jolt of high-voltage electricity. Flash units
are configured in a number of different ways:
|On camera flash
||These units (red arrows) are built right into the camera. This
is an advantage in that they are always handy, but:
- They increase the weight of the camera.
- They are underpowered.
- They draw their energy from the expensive camera battery, and can
drain it quickly.
- Because they are close to the lens, they may cause
"red-eye" in the picture.
|Hot-shoe mount flash
||Bigger and heavier, these units contain their own batteries (typically
inexpensive AA cells). They have more features, they are less
prone to red-eye (since they are further from the lens), and they can
often be mounted on extension cords or used with a wireless control
system for even more flexibility. This unit also has an infrared light
source (red panel) that helps the camera's autofocus system under dim
|Macro ring flash
||These units fit the flash head in a ring which mounts around the lens
of the camera. They can get the light on even close-in subjects,
but don't work well if the subject is more than a few feet away - and
talk about red-eye! The battery pack of this unit (left) fits on
the camera's hot shoe.
Whatever the type of flash you get, one thing to keep in mind is the Guide
Number This is a number, usually expressed in feet at a given ISO,
which indicates the relative power of the flash. A higher number means a
more powerful flash. For instance, two flash units may have guide numbers
of 50 and 100 with ISO 200 film. This would mean that the former is
powerful enough (with a normal lens) to illuminate a target 50 feet away.
The second unit is more powerful, since it would reach 100 feet.
Most flashes are designed to work at shutter speeds from 1/60 to 1/125 of a
second, this is called the sync speed. Newer cameras have a wider
range. On the other hand, the shutter speed is somewhat irrelevant in
situations where the flash will be the main light. Under these conditions,
the brief (thousandths of a second) flash burst will freeze motion.
Other factors affect the useful range at which a flash will work. A
wide-angle lens requires more light than a normal lens, for instance, because at
a given range a larger area must be lit. Some cameras and flash
communicate with each other; the hot-shoe flash shown above can find out from
the camera what lens is mounted and then zoom the flash head (automatically, via
a motor) to provide the right angle of flash to complement the lens.
Multipliers, extension tubes and other accessories may also affect flash
Flash used to be a tricky business, but electronics has changed all
that. Newer cameras either read the flash exposure by measuring the light
as it is reflected off the film itself during exposure, or they fire a pre-flash
and use special metering cells to determine the proper flash exposure. In
the former case, the camera simply shuts off the flash when the right amount of
light has reached the film. In the latter, the camera simply fires the
flash for the correct amount of time. Most cameras can easily do
"fill-flash" as well. In fill flash, the camera makes an exposure
using the natural light that is very close to correct, and fires the flash for a
very brief time. This brief burst of flash "fills" in the
shadows and brightens colors. Because the exposure was largely made using
ambient light, however, objects in the background appear normal, not black as
can happen when flash is used as the main light.
If you are using flash in any of the modes mentioned above, remember that
large objects or objects close to the flash will reflect a lot of light back at
the flash. If they are large in the field of view, they can adversely
affect the exposure, if they are small they will likely be over or underexposed
themselves. For instance, a blade of grass in the foreground of a macro
shot may become completely white in the image, or the camera may use so much
flash trying to turn a black dog into a gray one that the rest of the picture is
Some hints on flash:
||1. Use extension cords or wireless remote units to get the flash
away from the camera.
||2. If the flash is too harsh (particularly with close subjects),
use a softbox or place a tissue over the flash head.
||3. Many flash units have a bounce capability, which allows you
to swivel the flash head and bounce the light off a ceiling or
wall. This results in a softer, more natural light.
|This only works if the ceiling or wall is close.|
|This requires a more powerful flash.|
|Don't try this with a colored ceiling or wall!|
If there is no ceiling nearby, another accessory, a pocket bouncer,
will fit on the flash and serve as a surface for bouncing.
|4. Beware of shadows cast by objects caught in the
|5. Fresher batteries will allow the flash to recycle
faster. Also, the flash will recycle faster when the subject is
light colored and close. Dark, distant objects will use up all the
flash's power and cause a longer recycling time. Pressing the
shutter before the flash has recycled may result in a blurred or dark
||6. Many flash units have a test button and a flash confirmation
light. Firing the test button will produce a flash; if there is
enough light the confirmation light (usually green) will come on.
This lets you know if you have enough light before you waste film.
|7. On overcast or rainy days, fill-flash can bring
||8. Some flash units have a slave feature. This
means that they will fire when they detect a flash from another
unit. This is handy in two cases:
- You are a victim of a media circus. Hold your slave unit in
front of you and it will fire a blinding flash into the camera of
anyone who tries to take a flash picture of you.
- You want to add additional light, perhaps from a flash unit closer
to the subject, but don't want to string wires all over the place.
|In the second case, an accessory even more useful than the
slave is shown in the image above left. The TTL slave sensor works
with automatic cameras and flashes. Not only can it sense when the
flash is firing (and trip its own unit), it can also sense when the
camera has sensed enough light and is turning the main flash down.
At this point the TTL slave unit shuts off its own flash. The
result - automatic, wireless remote flash exposures. Some camera
manufacturers are now building this feature into their own
flashes. I use the add on unit, shown here velcroed onto the top
of my flash unit. When coupled together by an off-camera extension
cord, this makes for a more compact rig than you get when simply
attaching the flash to the built-in hot shoe on the slave sensor.
With my macro
rig set up on a tripod, I can hold the flash/slave unit at the
precise position to augment the light from the ring flash. I use
control or the camera's self timer to trip the shutter.
A Flash Extender can allow you to use a flash with a telephoto
lens at greater distances than the flash would normally reach.
Flash extenders focus the flash light.