Amateur Photographer - UK (2019-06-08)

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Tech Talk

essor Newman on...

BobNewmanis currentlyProfessorof ComputerScienceat theUniversityof Wolverhampton.Hehasbeenworkingwiththedesignanddevelopmentof
high-technology equipment for 35 years and two of his products have won innovation awards. Bob is also a camera nut and a keen amateur photographer

n the Triangle

W

henI studied
photography
backin the
1960sthe
exposuretrianglehadn’tbeen
invented.It firstappearedonlyin
1990,in BryanPeterson’sbook
UnderstandingExposure, underthe
name‘thephotographictriangle’.
Thethreesidesof thetrianglewere
aperture,shutterspeedandfilm.
Therewasnographicto support
thewrittendescription.Bythetime
of thebook’ssecondedition,in
2004,the‘film’sidehadchanged
to ‘ISO’,presumablyin response
to thedevelopmentof digital
cameras,whichhadanISOcontrol.
Subsequently,thetrianglehas
becomea digital-agephenomenon,
withthemajorityof introductory
tutorialsonphotographydeploying
thisdevicesomewhereortheother.
It hasbecomesoubiquitousthatI
haveseenit referredto in articles
aspartof thefundamentaltheory
of photography.It wasneverthat

• hadit been,it wouldnot
  havebeenpossibleforseveral
  generationsof photographersto
  practisebeforeit wasinvented.

Misleadinginferences
Formyself,I haveneverbeen
ableto workoutexactlywhatthe
triangleis intendedto convey.Not
manyof thetutorialsthatusethe
triangleactuallysayanythingabout
this,andit isn’tobviousfromthe
geometry.Therelationship
betweenaperture,shutterspeed
andISOdoesnotobeythe
geometricalrulesof a triangle.I
havebeentoldthatthetriangle
impliestheremustbea ‘balance’
betweenthethree.Oneunhelpful
factoris thatthepeoplewhoteach
usingthistriangledon’tseemto
agreeonthemorphologyof the
diagram.In theillustrationabove
are 20 differentversionsof the
triangle. They differ in important

aspects:in some,thethree

parametersarerepresentedbythe

sidesof thetriangle;in othersthey

arerepresentedbythecorners.

Thearrangementof the‘darker’

and‘lighter’endsof thescalevaries

amongthosewhochooseto label

thesides.In some,forallthree

cornersit is a lightendadjacentto

a darkend;in otherstheaperture

andshutterconvergeto a dark(or

light)pointandtheISOconnects

twolight(ordark)points.Some

areadornedwithscales,which

suggeststhereis somecalculation

thatcouldbeperformedwiththe

triangle;othersareplain.

However,of moreconcernis the

factthatseveralof thesetriangles

containfalsestatementsorimply

thingsthatarenottrue.Fourof

themplacetheword‘exposure’,

suggestingthatthethreesides

togethermakeuptheexposure.

Thisis incorrect.Exposureis the

illuminanceat theimageplane,

andis controlledbythescene

luminance,apertureandshutter

only.(Thereasonthatchanging

ISO changes exposure on your

camerais thatit setsthemetering

to a differentexposure).Severalof

themlabeltheISOside‘sensitivity

to light’andsome,worse,saythat

a higherISOgives‘morelight’.This

is wrong.Thecamera’ssensor

doesn’tbecomemore‘sensitiveto

light’asyouraisetheISO;neither

doesmorelightbecomeavailable.

Then,thereis thesuggestionthat

raisingISO‘increasesnoise’.Thisis

a misattributionof causality.As

saidabove,raisingISOadjuststhe

meterto seeka smallerexposure,

andit is thatsmallerexposure

whichmakestheimagenoisier.If

youraisedISOwithoutadjusting

theothertwocontrols,theimage

wouldbeslightlylessnoisy.

It’ssadthatmanyphotographers

makethesamemistakeswhen

workingwithexposure,andit’s

possiblethatthisarisesfromthe

misleadinginferencesthatcome

fromthetrianglediagram.It could

alsojustbetheteachingthatgoes

withit. EverysingletutorialI have

seenthatusesthetriangleasa

pedagogicaidincludes serious

errors in its text.

Whatexactlyistheexposuretriangle?Seemslike

there isn’t a single consensus on this subject

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Willtherealtrianglepleasestandup?Thereseemstobeno agreement on
how the exposure triangle diagram should be presented