10 Things Youshould Know About Flash

8/10/2019 10 Things Youshould Know About Flash

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L I b H T I N b H O W T U

I

sin

a

Canon

Spaedlite

540EXhigh

on a tripod

Gary William-

son made

these sun-

flowers pop

against a

dark sunset

W e m aintain that the s ingle m ost important acces-

sory for your

DSLR

is a full-featured T T L flash unit

W ith lightning in a botue, yo u can freeze action

solid, m im ic studio lighting, tam e harsh m idday

sunlight, balance o r unba lance) the color inascene,

an d produce w ild and w eird effects^with n o soft-

warerequired.Here w e presen t a primer on portable

flash th eory a nd practice.

B y D a n

i c h a r d s

^ All flash ph o

are double

exposures.

The two exposures occur

neously one by the am bie

the other

by

th e flash illum

tion.

Youc an vary each of

expo sures for a wide varie

different effects: You can m

them of equal hrightness

uneq ual or widely uneq ua

can give th em different co


2/6

u can even vary

tter effects, with one exp osure

urred and the other

p. This is what mak es

photograph y so muc h fun

EXPERIMENT

If you're

shooting, say, a foreground

leafy

, don t settle for the auto

ary both the am bient a nd

erent effects.

Adjusting the

aperture affects

both ambient

sthe apertureisthe lens's light

, opening it up or stopping it

lighten or darken both

esprovided the flash out-

tiskept at the same level. (With

eflashset to auto, itwillcompen-

byincreasing or reducing the

m ore on thisbelow. Since

large aperture admits a lot of light,

eflashcan emit less for proper

This will giveyou greater

reach and/or longer battery

Asmall aperture requires more

, and you r reach an d/or battery

USING A W IDE

aperture to

limit de pth of field in an outdoor

force

to exceed your camera's m axim um

debar, page 118 ).

a neutral-density (ND) filter

p (ND 1.8) filter will let you

op to V 2 5 0 sec from

1/8000

sec,

autofocus dicey.

Shutter speed

affects ambient

but no t flash

The flashISa very

ef burst occurring du ring the

tter openinga flash bu rst of

sec will provide the sam e

umination with a shu tter speed

Bounce

flash can

eat up flash

powernot

just because

of the extra

distance the

light must

travel, but

also because

even quite

reflective

walls or

ceilings

absorb

someof

thelight.If

your bounce

shots are

turning

out under-

exposed,

open up the

aperture.

of 1/30 sec as itwillwith a 1/250

sec shu tter

So

you can lighten

or darken the ambient exposure

by increasing or reducing the

shutter speed while maintaining

the same apertureand thu s the

same flash output.

YOU CAN VARY

theshutter

speed and still use autoexposure

ysetting the cam era to aperture-

priority mode. Now, when you darken or

brighten with exposure compensation,

the cam era will vary the shutter speed

but keep the aperture the same.

4

For na tural-

looking nil flash,

underexpose the

flash ex posure.

The idea behind natu ral nil is to

ma ke it look like soft a mb ient

light. As fill flash is o rdina rily

used for back- or sidelit sub-

jects, setting the flash illumina -

tion to the s am e level as the

amb ient l ight makes your strobe

obvious.Tokeep it subtle, use

the flash's exposure compen-

sation to dial down its o utpu t.

Settings in a range of-0.7 to -2

EVusua lly work well.

DON T FEAR

unnatural

fi l l.

For exam ple, a

2 stop

ambient

underexposure combined with full

flash exposure can dram atically isolate

a hum an figure or foreground object.

Flash h as

c o l o r .

While we

think

of flash as white light,

flash, like all visible

light

has a

color

cast.

Accessory flash m anu -

facturers set daylight balance at

around 5200-5500 degrees Kelvin

in color tem pera ture. This is actu-

ally a good deal wa rmer in color

tha n daylight on a blue-sky day

when color temp erature can go

as high as 10,000 degreesK(very

blue), leading to a mism atch in

color balance .Thisis why digital

cameras have se parate presets for

flash and daylight white balance.

Amore common mismatch:

flash with tungsten room light.

With a digital camera se t to flash

white balance, the foreground

subject will appear a neutral color

while background illumination

ou t of the range of the flash will

have a yellow-red cast. (Many

photographers like this look and


3/6

se t

it

up de liberately) Flip

the

camera s w hite balance

to

tung-

sten,

and

the background light

will shift to neutr al w hile

the

fore-

ground subject ap pears very blue.

Wan t to even the balance? Putan

amb er filter over the flash lens,

and set the cam era to tungstenor

auto white balance.

W I TH H L M you may

need toad danextra step

to coior balancing . Shoo ting daylight

fi lm under fluorescent l ights,

you

would put agreengel CC30)over

the fiash head tobalanceit withthe

greenish fluorescents. You

d

then

place

a

mag enta fi lter such

as the

Tiffen FL-D) over

the

came ra lens

to

neutralize thenow-overall green cast.

6

Autoflash varies

the duration

of the flash.

Modem accessory flash units

automate exposurebyreading

the bounce backof the flash

through

the

len s (TTL). (Many

uni ts

now

make this reading

via

a

brief preflash.)

The

camera/flash brain adjusts

the flash exposurebymaking

the burst shorterorlongerfor

lessorm ore light, respectively

The rangeoff lash bu rstsis

pretty astound ing a t5rpi-

cal accessory unitmayhave

durations from 1/1000 sec to

1/50,000

sec oreven less.

You also adjust manua l flash

power by changing duration,

almost always measured in frac-

tions:fullpower, 1/2,1/4,1/8,

etc., o ften down

to

1/64 power

for the shortest flash duration.

^ USE VERY BRIEFflash

^ ^ dura ti onsforextreme m otion-

stopping photos. Positioning the

f lash close toyour subject, usinga

wide aperture,and settingahigh

iSO w illall shortentheduration

of autoflash,andyoucandialin

high speed m anually, too. Keep

WithAA

batteries,

there is

no

free lunch:

Thebatteries

that give

youie

shortest

recycling

times,

NiMH

rechargeables,

giveyou the

fewest shots

per charge;

the ones

tha t give

youie

most shots,

disposable

lithiums,

havethe

longest

recycling

times.Alkaline

AAsland

in between.

the ambient l ight and/or ambie

exposure iow, though ,oryou m

just capture a ghostthe te rmf

ambient motion biurin afiash

TTL flash wor

better with the

camera in ma

exposure mode.

By

setting the am bient expo

you wa nt m anually, you elim

one variableand canconcen

ontheeffects of various flash

exposu res, positions, etc. Say

you re shootingaseriesofpo

traits outdoors withillflash

wantanambient exposure t

keeps the backgroundat ace

light level,butwiththecam

set to auto,itmight keep adj

this exposure as you change

position, focal leng th,or flas

outp ut. Better to lockitin u s

manual mode.

WITH l UFLASH in a

situation, it soften better

se ttheambient exposure1 sto

a litt le mo re overthemeter rea

This m akes thebacklighting ap

more reaiistic. With portraits,it

heipstoobscure background d

8

Flash follows

same hardnes

softness rules

ambient light

The broaderthelight source

softer the

light.

That s why s

portraits shooters use softbo

umbrellas,andbeauty dishe

their strobes. But the narrow

light source, the hard er the l

Sostudio shooters usesnoo

and gridstoget hard, even h

effects. Placing the light sour

closer to your subject mak es

broaderandtherefore softer

ing the light source farther a

makesitnarrowerandhard

Readallabout the qualities

light in 10ThingsYouMust

AboutLight in

our

May 201

or

at

PopPhoto.com/lighting

CONTINUESONP


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OTIO

TRAIL

A 1 4 0

shutte

burst f

Niko n

Speed

gave C

Walbe

trai l in

I I That Syncing Feeling

Film and digital SLRs use focai-piace shuttersessentially curtains th at ope

and close to mak e an exposure. The curtains m ust be fully open for the flas

exposure, and these events are synchronized eiectronically in the cam era. B

at faster shutter speeds (depending on the ca mera , faster than 1/160 1/2

or 1/250

s e c ,

the curtains never fuily expose the focai plane.

Instead,

the

achieve high-speed exposure by traveling as a s lit across the focal plane.

Fire a flash during this exposure, and you'll have either a thin siice of flas

exposure or no flash im age. Fortunately, most mod em DSLRs have a failsa

that prevents you from setting the wrong sync

speed,

even in m anua i expo

iVIany m anufa cturers '

T T L

flashes offer highsp eed sync, a workaround th

puises the flash rapidly as the narrow slit traverses the focal

plane.

This giv

you flash sync at the fuil range of shutter speeds, at the price of iim ited dista

range. Good uses: fill for fairly close action subjects, or for outdoor portraits

taken at wide-open apertures that might man date very fast shutter speeds.

Rash sync is usuaily triggered at th e start of the shutter cycle. With mo ti

biur pius

flash, though,

this gives the weird effect of the subject mov ing ba

wards. Rear-curtain or trailing sync fires the f ash at the end of th e exposure

ma king for the trailing blur you see in the photo above.

I

NUMEROUS iight-modifying

devices are m ade for shoe-

mountflash,as well as accessories for

adapting shoe-mounters to studio gear

such as stands, umbrellas, and so forth.

Flash falls off

in proportion

to the square of

the d istance.

The beam from a flash unit is

cone-shaped shoot a relatively

close object and most, if not all,

of the light co ne will cover it As

you move farther

away,

though

a smaller portion oft he light

cone hits the subject, as more

the light sprays w ide. At a grea

enough distance, the flash s lig

becomes imperceptible to the

eye as well as to a sensor or fi

And it s a sq uare relationship:

you move tw ice as far away fro

your subject, you get only 1/4 t

illumination on the subject; tri

your distanc e, and you get only

the light. Setting the zoom hea

an accessory flash to tele posit


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l create a narrow er

cone,

bu t

Y et

jus t becaus e you re far

om your subject doesn t m ean

has tob e . Y o u ca n

and fire from a

P US E FLASH FALLOFF to

* ^ your advan tage by varying

nce t>etween your subject

r subject mov e

For exac t

control over

a multiflash

witch them to

sure,

the major

L fiash system s can operate

and you can vary their out-

ireless controller. But

s pretty easy to adjust multiple

s using the ma nua l frac-

A quick starting p oint for a

fill and back-

e fill for

FOR ELABORATE

FLASH

setups and s tudio

provides

ke readings of m ult i-pop

n mm

to am bient readings,

for balanc ing exposures. O

o r am a

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10 Things Youshould Know About Flash

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