Practical Photography - UK (2020-01)

PRACTICALPHOTOGRAPHY.COM 71

Know Your Stuff

Justhowoldis

photography?Who

in ventedit, andwere

th eythefirstpersonto take

a photograph?

AamirBashin,Birmingham

Adamsays:Cameraswerein use

lo ngbeforethefirstphotowas

ev ertaken.Thecameraobscura,

li terallymeaningdarkchamber,

was a darkenedroomwitha

smallholein oneside.People

fo undthatan upside-down

imageof thescenewouldbe

pr ojectedontotheoppositewall

in sidethe camera.Artistswould

us e thisas a drawingaid,tracing

ov ertheprojection,as farback

asthe16thcentury.

Then,in 1825,alongcamea

Fr enchinventornamedJoseph

NicéphoreNiépce,who found

th atby usinga cameraobscura

and bitumenof Judea,which

hardenedin sunlight,hecould

capturescenesdirectlyonto

a pewterslate.He called

th e processheliography– sun

drawing.Picturedaboveis the

ol destsurvivingimagefromthis

pr ocess.Theexposuretimeis

believedto be anywherefrom

ei ghthoursto threedays,andit’s

consideredthefirstphotograph.

Who invented

photography?

What is a stop of light?

Whatdoesit meanto increase

myexposureby 1 stop?

Colin Anderson,Leith

Bensays:A stopoflightis a unit

measurementof exposurevalue.It’sa

measureof increaseor decreasein light

in tensity.Specifically,it is a doubling

ora halvingof theamountof lightthat

re achesyoursensor.So,if youincrease

yourexposurevalueby 1 stop,youare

le ttingin twiceas muchlightto your

se nsor.Decreasetheexposureby 1 stop

and youarehalvingtheamountof light

th atreachesyoursensor.Stopsarean

easywayto linkthethreeexposure

controls– shutterspeed,apertureand

IS O.Camerasusuallyworkin thirdsof

a st op,so an increaseof oneclickon

th e commanddialwill resultin a change

ofone-thirdof a stop,whilethreeclicks

wi ll giveyoua fullstop.

I want to try shooting long
exposures on film, but film is
expensive and I don’t want
to waste shots. What are the things
I should be looking out for?
Ellie Able, Dorset

Ben says: Unlike digital,
film becomes less sensitive
to light the longer it
is exposed for. This
has been given the
technical term
‘reciprocity failure’,
which in essence means
the longer you expose
your film for, the lesseffect
any further exposurewill
have. So what does thismeanfor
your photographs?
This phenomenononlykicksin after
about half a second, so for any exposure
longer than that, you’ll be getting
inaccurate readings from your light
meter. You will need to increase your

exposure beyond the value your camera

suggests in order to achieve a correctly

exposed image. How much you have to

adjust by depends on the film stock you

are using. For example, black & white

film such as Ilford FP4 requires you

toincrease your exposure by

an exponent of 1.26. A 10sec

exposure then becomes an

18sec exposure. A 2min

exposure becomes

nearly 7mins.

To find out how

much to compensate,

you should check with

your manufacturer, as

they will usually supply

long exposure guidelines

foreach of their film stocks.

Bearin mind that, unlike black &

white,somecolour film can develop

a colour cast as the different emulsions

within the film undergo reciprocity

failure at different rates, and you’d need

to use coloured filters to correct this.

Are exposures on film

the same as on digital?

MOIAN ADRIAN

LIGHTFIELD STUDIOS

DRAGON IMAGES

TIP

USEA

CALCULATORAPP

Thankfullythesedaysthere

arereciprocitycalculator

appsavailablethatwill

calculateyour

ex posuretime.