Amateur Photographer - UK (2020-04-18)

subscribe 0330 333 1113I http://www.amateurphotographer.co.ukI 18 April 2020 55

Tech Talk

ofessorNewmanon...

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

Proprioception

M

odernphotography
seemsto be
dominatedby
obscurejargon,so
I thoughtI’dtaketheopportunityto
introducea bitmore.Thesubjectof
thisarticleis ‘proprioception’,a
medicaltermfortheabilityto
sensethepositionof thebody and
itspartsin relationto the
immediateenvironment.
Proprioceptionis sometimes
referredto as‘thesixthsense’and
is of greatimportanceto
photographersof movingsubjects,
suchassportsandbirdsin flight.To
tracktheactiona photographer
needsto beableto sensehand
positionandtheeffectthatit will
haveonthecamera’sfieldof view,
allthetimeupdatingthatposition
in responseto othersenses,
includingtheeyes,and
proprioceptionitself,thepositionof
theheadandbodyandthe
informationthatgivesonthe
relativeorientationof thecamera.
I dida littleresearchat
physio-pedia.com,a websitefor
thephysiotherapyprofession.It
says that ‘proprioception is

basicallya continuousloopof

feedforwardandfeedbackinputs

betweensensoryreceptors

throughoutyourbody and your

nervoussystem.’

Feedbacksystems

Toanengineer,theidentification

of somethingas‘feedback’

triggersconcernsaboutsystem

stability.Feedbackis a very

powerfultechniqueusedin every

branchof electronicengineering.

Negativefeedbackcanbeusedto

makepowerfulcontrolsignals

preciselyfollowa smallsignal’s

instructions,henceit is used

extensivelyin poweramplifiers,

roboticsandindeedany

applicationin whichpowerneeds

tobeappliedprecisely.Where

negativefeedbackhastheeffect

of decreasingerrorsin application

of force,positivefeedbackhasthe

effectof increasingthem,causing

instability.Forthisreason,positive

feedbackis usedonlywhen

controlledinstabilityis actually

wanted,suchasoscillators,which

areusedtocreate a continuously

varying signal.

Feedbacksystemsneedtobe

carefullydesigned(orevolved).In

particularanydelayin thefeedback

loopcantransforma stablenegative

feedbacksystemintoanunstable

positivefeedback.Theproblem

appearsif thereis someperiodic

motionor resonancein thesystem.

In a resonantsystem,theeffectof

a changedependsonitsplacement

withinthecycleof thesystem.

Imaginepushinga childona swing;

to keeptheswinggoingthepushes

havetobetimedin phasewiththe

swing’smotion.If youpushasthe

swingis returningfromitsmaximum

thenyouwillincreasetheamount

of swing.If youpushjustbefore,

youwilldecreaseit. A delayin your

pushcanchangeit fromonethat

dampsdowntheswingtoone

whichincreasesit.

Now,toreturntothe

photographer.Holdinga camera

witha lensin herhands,sheis

constantlyapplyinganactive

stabilisationtowhatis a resonant

system– themomentof thelens

alongwiththeflexibilityof thehands

providesa naturalfrequencyof

movement.Thefeedbackloopis fed

byinformationbothfromtheeyeand

fromproprioception,andgenerally

thebrainwillperformwhatis called

a ‘datafusion’operationonthemto

identifyandcorrectforanydelayin

thevisualinformation,whichis why

electronicviewfinders,whichmust

inevitablyincursomedelay,arestill

quiteusableforthistask.However,if

weaddintothistheuseof thevisual

informationtotrackanerratically

movingsubject,it is possibleforthe

impulseprovidedtotipthecontrol

systemintoinstability.I speculatethat

somepeoplearelesssusceptible

thanothers,andthatthebraincan

adaptwithenoughtraining,butit

remainsa reasonwhy,at present,

opticalviewfindersarepreferred

for action photography.

Photographersofmovingsubjectsneedtopay

great attention to the body’s ‘sixth sense’

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Themovementhereis irregular,andthereis littletimeforacquisitionofthe
subjectasit appearsatthesideoftheframe.Suddencorrectionsfromthe
photographer could cause instability using a viewfinder system that incurs delay

© BOB NEWMAN