flash superimposes a frozen image from the flash with
one recorded by available light. The dancers'
movement is recorded as a blur--a trailing blur when
second curtain sync is used.
© 2002, Jack Neubart, All Rights Reserved
You can go your entire life
using a 35mm SLR and its built-in flash without ever buying an accessory
electronic flash unit. If you don't mind compromise. The built-in
flash takes fairly long to recycle and may not be ready when you are
to take the picture; it has limited reach, to perhaps 10 or 15 ft; redeye-reduction
mode wastes precious time that may result in lost picture opportunities;
and this type of flash doesn't leave much room for artistic expression.
On top of which, the built-in flash proves a serious drain on the camera's
batteries. So, after coming to the conclusion that an external flash
can be useful, where do we start? The obvious and first choice is a
An accessory flash is, admittedly, an added expense. But it need not
be expensive. Just don't expect any bells and whistles from a
truly inexpensive model. The good news: you can get a very functional
flash for under $100.
flash units offer an economical choice. The sensor on the
front determines flash output. This strobe is different
in that it features a secondary flash head, which serves
as a fill light when the flash head is aimed at the ceiling
for bounce flash. Another feature on this flash is its manually
zoomed flash head. This flash also houses the auto/manual
selector switch on the front, color-coded to match the two
usable f/stops for any given film speed.
A good, economic starting point is an auto-sensor, or, simply, automatic,
flash. And it's fairly easy to use. If you were using a strictly
manual flash, or using this flash in manual mode, you would have to change
the f/stop on the camera lens for each change in flash-to-subject distance--if
you or the subject moved relative to each other (it has to do with that
pesky inverse square law, light falloff, and distance). With automatic
flash, one f/stop covers a range of distances, so you have considerable
leeway. However, if you step outside this range, you'll have to
change the auto setting on the flash, with a corresponding lens aperture
setting, to accommodate the increased distance. But you'll still
be covered over a fairly wide range. The on-board flash calculator (dial,
sliders, or table), coupled with distance readings from the lens barrel,
is your guide.
Automatic flash units gained
popularity for another reason. They incorporate thyristor circuitry that
more efficiently uses the energy stored in the flash unit's capacitor,
in essence recycling unused energy and channeling it back into the system,
resulting in shorter flash durations and faster recycling times. This
means that the flash would be ready sooner--all based on the auto-sensor
reading, plus batteries effectively go further. As an analogy, think of
a refrigerator closing automatically (and saving energy) the moment you
made a decision, instead of waiting to be manually closed, which means
you'll be able to open it again sooner (less time required for the
vacuum seal to re-pressurize).
A typical use of electronic flash is freezing movement.
The use of an auto-sensor, shoe mount strobe ensured the
very short flash duration required to stop motion with this
fast-spinning pottery wheel.
Select flash units even let
you use power ratios, using less energy to start with. This option may
exist for manual or automatic mode--it varies with the flash. Often it's
used to support a winder mode, but works equally well if you know a nearby
subject needs less light: Start with less, and save.
For auto-sensor flash to work
properly, the sensor must remain aimed at the subject. If you tilt or
rotate the entire flash unit that orients the sensor incorrectly, which
will result in an erroneous flash exposure. Fortunately, most flash heads
can be tilted or swiveled independently, with the sensor in place, in
the original orientation, thereby preventing exposure error. Exposure
settings with automatic, as well as manual flash need to be adjusted when
most filters and lens extension are used to prevent underexposure.
TTL auto-flash, or simply TTL
(Through The Lens) flash, bypasses the need to interpret a flash calculator
because the flash receives all this data from the camera. With a few key
settings in place on flash and camera, you're ready to go--with
all data digitally displayed (where LCD panels are employed). Because
light readings continue to be TTL, the use of filters and lens attachments
is accommodated when the flash is directed to deliver its burst of light.
TTL flash units often boast added functionality, with prices to match,
easily costing up to several hundred dollars with all the bells and whistles;
much less for modest TTL units.
This young couple withstood the freezing cold to provide
an opportunity to illustrate balanced fill flash against
a dusky backdrop. TTL flash simplifies the use of flash
fill, by taking ambient light levels into consideration.
Making Attachments: The
With a built-in flash, all the triggering circuitry--the stuff that tells
the flash when to fire--is internal. An external flash needs a little
extra, aside from its own batteries. Most flash units at the very least
have a "hot shoe" contact at the base, or "foot,"
of the unit, in the form of a pin, which matches a similar contact point
in the camera's hot shoe (routinely situated) atop the penta-prism
housing--although some pro-level SLRs may not be equipped with a hot shoe.
Releasing the shutter sets in motion a triggering process that results
in the flash firing, with information relayed through this contact point.
This normally follows the opening of the first shutter curtain. The camera
shutter speed that ensures synchronized operation with conventional flash
units is called "X sync."
As cameras and flash units
became more sophisticated, the simple individual contact point became
an array of matching multiple contacts (two or more--on flash and camera).
We moved from simply providing the means to trigger the flash to adding
some level of microprocessor-controlled electronic communication between
flash and camera. Flash units were now "dedicated." Whereas
earlier, any hot shoe flash could be used with any hot shoe capable camera,
now the flash had to be matched specifically to the camera model (or system
camera). This dedicated connection tells the camera--and you--when the
flash is ready to fire (fully charged) and sets the correct flash sync
speed on your focal plane shutter SLR automatically (assuming basic settings
are in place).
Automatic flash units have a flash calculator that indicates
the usable f/stops for a given range of distances, for a
given ISO/ASA. This one is slide-rule style; others are
dial-shaped. Either way, use the f/stop that will cover
the greatest distance you and the camera/flash expect to
be from the subject. Then set the elector switch to the
matching color-coded setting. Use the lash-test button as
confirmation (an LED lights to indicate adequate auto coverage).
At the top of this flash, you can also see the bounce flash
angles--click stops used to tilt the flash head. Other flash
heads may also swivel, for added versatility.
Why does sync speed matter?
With focal plane shutter cameras (the typical 35mm SLR), if the shutter
speed set on the camera is too fast, the shutter curtain movement and
flash burst are out of sync and only part of the frame is exposed to flash.
On the other hand, when too slow a speed is used, the ambient light may
be enough to record a secondary, ghost image--which many photographers
actually use to advantage, to add depth or a dynamic element to the picture,
when done well.
Making A Truly Dedicated
The next step up in dedicated technology is TTL auto-flash. Thanks to
an enhanced pin/contact base array (which may be permanently attached
or modular), all information is electronically transmitted not only from
the camera to the flash, but also back from flash to camera--and to levels
heretofore unknown, to provide the highest degree of accuracy in a flash
exposure with the greatest versatility. This may involve a pre-flash that
measures subject distance. Different camera technologies have their own
way of measuring the flash, involving one or more sensors, but in each
case, the light is measured through the lens--hence TTL--and off the film
plane, and possibly tied into autofocusing.
Owing to its sophisticated electronics, TTL flash may be made to work
with the existing light, automating and simplifying the process of fill
flash. Depending on the camera and flash combination, the flash may actually
reduce output so as to provide a more natural level of fill. However,
you may still have to correct for subject brightness.
Zoom, Bounce, Twist
The simplest flash unit features a stationary head. More capable units
may appear possessed, Exorcist fashion--practically spinning about on
an axis, nodding their head, and magically zooming. How much of this do
The automatic flash unit on the left features multi-dedicated
flash contacts, which means it can be used as a dedicated
strobe with a variety of SLRs. The flash on the right can
only be used with specific camera models with TTL flash
capability, from one manufacturer. The topmost pin is used
to help secure the flash in the hot shoe, which has a similar
dedicated pin array. Note: normally, automatic strobes are
dedicated to one camera/series.
A zooming head largely does
away with the need for accessory wide angle and telephoto panels to match
the lens focal length and more efficiently use the light. Zooming is automatic
(often with manual overrides) on TTL flash, and largely transparent to
the end user, except for some LED or LCD indication on the flash. Other
flash units may be equipped with a mechanically operated zoom head, with
concomitant changes in the unit's appearance. Where an override
option exists, use the tele-zoom setting to spotlight a person, or limit
the reach of light at the wider settings. (The flash may also feature
a built-in, manually positioned super-wide panel, to accommodate even
shorter focal lengths.)
Bounce flash requires the head
to tilt upward, at the very least, although a nearby wall may prove a
more suitable reflecting surface--hence the swivel movement. Because overhead
bounce flash tends to produce harsh shadows under the eyes, select strobes
feature a built-in secondary flash tube, that, when activated, shunts
some power away from the main flash head in order to provide fill.
TTL flash units employ various technologies to assist in
outputting the proper amount of light. Zooming on this flash
is internal, and designed to automatically match the lens
focal length, within reason. Manual zoom overrides are available
here, but not on all auto-zooming strobes.
Some strobes also feature a
downward tilt, for close-ups. With the flash seated in the hot shoe, this
downward, or negative, tilt may result in throwing the subject (partially)
in shadow, because the lens or lens shade is blocking the light. A more
effective solution would be to use the flash off-camera, with a sync cord,
while diffusing the light, or to employ a ring flash or other flash specially
designed for macro work.
Even with ultrahigh-tech flash units, the concept of a Guide Number remains
in vogue. It provides a measure of the unit's output, telling us
how potentially powerful the light is. The higher the GN--Guide Number,
the greater the output, assuming a level playing field--measured at ISO
100, at full power, at a standard focal length (if zooming/without panels),
in feet. Don't expect much reach from a unit rated as GN 30, whereas
one with a GN of 130 will go pretty far. Zooming the head to a tele position
effectively increases the GN, with the reverse having a negative effect.
Note: If you typically find the GN of your flash to be overrated
(leading to underexposure) or underrated (overexposure), open up or close
down the f/stop, respectively. In other words, if you detect about a full
stop of underexposure--owing to an inflated GN, instead of using f/5.6
that the flash unit recommends, use f/4. Bracket exposures in half stops
to be safe. You, of course, have more leeway with print film than with
slide emulsions. Keep in mind that the GN rating is based on a flash used
in a normal sized room, with fairly reflective walls. Consequently, when
shooting in wide, open spaces or outdoors at night with auto-sensor, as
well as manual, flash, increase exposure by one-half to one full stop.
(Want to perform your own GN tests? Use this equation: GN (in feet) =
f/stop x distance (flash to subject, in feet), at a distance of 10 ft,
to simplify matters. You can then interpolate the flash calculator based
on your findings.)
Many TTL flash units feature an LCD panel for a digital
readout of settings. This flash also has a switch permitting
it to work in wireless TTL mode, and to act as the master/triggering
unit or as the slave/receiving flash. But considering the
high cost, maybe you can do without such esoteric functionality.
With flash, it is not the camera's
shutter speed that counts as part of the exposure. Instead, it's
the flash duration. So, in our classic E(xposure) = I(ntensity) x T(ime)
equation, "T" is now flash duration. "I" remains
the lens aperture, or f/stop.
Moreover, at any given film
speed, the f/stop determines the reach of the flash (without zooming the
flash head or using accessory panels): the larger the f/stop, the greater
the reach; the smaller the f/stop, the more restricted the distance covered
by the flash. (In other words, to keep a distracting backdrop in relative
or possibly total darkness, use a small f/stop designed to reach only
the subject. This may also render intrusive background shadows invisible.)
While a flash on-camera is convenient, the lighting that results is often
flat and harsh, producing hard shadows that may make it difficult to discern
the subject from the shadow directly behind. So, with conventional flash
units, we turn to a sync, or "PC," cord. This is our wired
connection from a terminal on the flash to another terminal on the camera,
traditionally the "X-sync" terminal. (Not all flash units
support a sync-cord connection.)
Dedicated auto-flash and TTL
flash cameras take this one step further. The cable fits into the camera's
hot shoe and extends from there to the flash. Or, the dedicated connection
may instead attach to an electronic terminal on the camera, with a locking
mechanism. A few dedicated automatic flash units allow the sensor to be
removed from the flash and mounted atop the hot shoe, seated in an adapter
with a cable attached for off-camera flash. Any way you look at it, this
design ensures a more secure connection, as standard PC cords have a tendency
to pull free or wear with use. Some TTL flash capable SLRs may still feature
X sync, for use with conventional flash units, letting you directly attach
a standard PC cord to the X terminal on the camera or indirectly to the
hot shoe, via a hot shoe adapter.
Unless you plan to hand hold
the off-camera flash, you'll need something to support it. One option
is to mount it atop a flash bracket. Flash brackets come in all sizes
and configurations. Some flash units today come with their own, convenient
miniature stand. Numerous TTL flash units also support wireless TTL flash,
when used together with the appropriate cameras.
Normally, AA-size alkalines are used in external shoe mount strobes, providing
the most number of pops, bested only by AA lithiums. Alkalines provide
fairly consistent performance and are easy to buy. Lithium cells are not
recommended for all flash units--only those specifically outlining their
use, as these batteries have a higher initial power surge that may damage
the unit. Most of the time, rechargeable NiCd (Nickel Cadmium) or Ni-MH
(Nickel Metal Hydride, nickel hydride, or NiHy for short) can be used.
But again, the manufacturer may advise against their use: there is a size
variance and the nickel cells may not make contact at both ends. Fortunately,
most flash units readily accept nickel-type rechargeables, even though
they are of slightly lower voltage than alkalines. Nickel rechargeables
recycle faster than alkaline and lithium. Caution: never mix battery types,
and always use batteries with equal energy reserves. Fresh (or freshly
charged) batteries are always best.
Replace the batteries when recycling times become excessive. Interestingly
enough, if you use a digital camera that also uses AA cells, you may find
that after the digital camera has bowed out, that there is sufficient
life left in the batteries to use them in your flash.