Amateur_Photographer_-_04_October_2019

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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

Time of flight

A

webrumourpublished
recentlystatedthat
Panasonicis planning
onemployinga time
of flightdepthsensorto aidwith
autofocusona forthcomingMicro
FourThirdscamera.Therumour
camefromthe‘4/3Rumors’site
undertheheadline‘Panasonicis
developinga newTOFMicroFour
Thirdssensorfora newPERFECT
autofocussystem!’.AsI’vebeen
workingontimeof flight(hereafter
TOF)systemsrecently,andthe
headlineabove(andarticleunder
it) hassomeseriousinaccuracies,
I thoughtI’dprovidesomebetter
informationforAPreaders.
Theheadlinesuggeststhatthis
is a ‘MicroFourThirdsSensor’,
implyingit is a photographic
imagingsensorwithrangefinding
capability.Thepossibilityof this
beingthecaseis highlyremote.
Timeof flightis anactiveranging
system;it is a formof LIDAR,
thelightversionof radar.LIDAR
systemscanfindtherangein a
numberof ways,butthemost
commonis TOF,wherebya pulse
of lightis emitted,usuallybya
laser,andthetimerequiredfor
thatpulsetobereflectedoffan
objectandreturnedtoa sensor,
adjacenttobutseparatefromthe
emitter,is measured.Considerthat
lighttravelsat 300,000km/sec.
If wemeasurethedistanceof an
objectat 100m,thelightwillmake
thattripandbackin two-thirds
of a millionthof a second,soour
rangefindingsystemmustbe
abletomeasureperiodsof that
duration.Thankstothespeedof
modernelectronics,thisis nottoo
challenging.Moreproblematicis
providingtherequiredaccuracy.
Focusinga camerarequiresmore
precisionat closedistances.An
errorof 10cmat theabove100m
would not affect accuracy of focus

much.Ontheotherhand,the

same10cmerrorat 1mdistance

wouldproducea substantially

out-of-focusimage.

Accuracyatcloserange

Traditionalfocusingsystems,such

asphasedetection(orsplit-image

rangefinding,whichis thesame

principle)andcontrastdetection

havethehappycharacteristicthat

percentageaccuracyincreasesat

closerange.Unfortunately,TOF

hasthereversetrait.Itsaccuracy

is determinedbythesmallesttime

intervalthatcanbeaccurately

measuredwithoutjitterornoise

affectingthereading.Whenwe

considerthat10cmrepresentsa

timedifferenceof 660trillionths

of a second,therequiredaccuracy

of timingcanbeappreciated.

Nonetheless,in thepastfewyears,

LIDARsystemswithcentimetre

accuracyhavebeendeveloped.

TheTOFimagesensor

integratesseveralTOFsensors

intoa pixelarray.These‘pixels’

havea radicallydifferentdesign

fromnormalimagepixels,and

aredesignedpreciselytofilter

out the ambient light on which

photographydepends.Soit’s

unlikelythetwofunctionscould

beintegratedintoa singlesensor.

Rather,anyTOFrangefinderwould

bea separateassembly,nota

through-the-lenssystem.It would

alsobea ‘rangefinder’asopposed

toan‘autofocus’system.The

distinctionis thata rangefinder

measuressubjectdistance,which

canbeutilisedtosetfocususing

scalefocusing,whereasautofocus

systemsactuallydetectthe

conditionof in-focus.Thus,the

headline,suggestingthatthis

wouldbea ‘perfect’autofocus

systemis wideof themark.That’s

nottosaythataddingTOFtoa

camerasystemwouldnothave

itsmerits.A smallIrishcompany,

CDA-TEK,specialisingin add-ons

forBlackMagiccinemacameras

hasrecentlydemonstrateda

TOFrangefindersystem.Thisis

wherethesystemcouldexcel,in

automaticfocus-pullingin video,

sinceit cangatherdepth

informationaboutthescenewhich

canthenbeusedtomakesmooth

andattractivefocustransitions.

Thismightverywellbethereason

why Panasonic has an interest.

Panasoniclookstobeplanningtoaddtimeofflightto

its camera system – Bob Newman clarifi es the rumour

CDA-TEKhasdemonstrated

thistimeofflightfocusing

system for BlackMagic cameras

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