Amateur Photographer - UK 2019-07-12)

18 6 July 2019I http://www.amateurphotographer.co.ukI subscribe 0330 333 1113

Technique

Whathasartificialintelligence

(AI)gottodowithautofocus?

Face-andeye-detectionAFhavebeenaroundfora
littlewhile,andtheyareusefulforsocialphotography.
EyeAFis especiallyhelpfulbecauseit getsthemost
importantpartof thesubjectrazorsharp,leavingyou
tofocusonaspectssuchasthecompositionandtiming
of yourshots.
Oneissuewithsomeface-detectionsystemsis that
theyincorrectly‘see’faceswheretherearen’tany,
whichleadstofocusingerrors.Forthisreason,it’s
a goodideatoturnthefeatureoffwhenyou’renot
goingtouseit.
Thankstoincreaseduseof artificialintelligenceand
greaterprocessingpowerit seemslikelythatwe’llsee
moresubjectsbeingdetectedautomaticallyin thenear
future.SonyhasnowextendeditsEyeAFsystemto
coveranimals’eyes,orat leastcats’anddogs’eyes,
andOlympus’sOM-DE-M1Xcandetectcars,trains
andaeroplanes,whilePanasonic’sLumixS1andS1R
candetectanimals.Theyallworkwell,makingit easier
togetthosesubjects’sharp.
EventhoughmodernAFsystemsareincredibly
smart,thereareoccasionswhenit’sbetter,orperhaps
easier,tofocusmanually.Camerasusuallysearchthe
distancefortheirtarget,whichmeansthatit canbe
quickertofocusmanuallyona macrosubject,for
example.Andif you’reshootingthroughsomethinglike
watersprayfroma fountain,orfoliage,theAFsystem
is likelytogetverydistracted,thusmakingmanual
focusinga betterchoiceheretoo.
If you’reusinga DSLR,don’tstrugglewiththe
tinyviewfinderimagewhileyoufocus.Instead,
activateliveviewsothatyoucanmagnifythefocus
pointandusefocuspeaking to get the subject
completely sharp.

Whyusethe

backbutton?

Evenwithhighframe

rates,it’simportantto

timeyourshotscarefully.

Back-buttonfocusing

canhelpwiththisby

takingawaytheshutter

release’sAFactivation

duty.Instead,youuse

theAF-onbuttononthe

backof thecamera(or

viaa customisedbutton)

tocontroltheAFsystem,

andonlypressthe

shutterreleasewhen

youwanttotakea shot.

Thisis especiallyuseful

whenyou’recapturing

action.Withmotorsports,

forexample,youmight

wanta cartoappearat

theapexof a bend.To

helpwiththis,youcan

setthefocuswiththe

AF-onbuttonandit

won’tshiftwhenyou

presstheshutterrelease

to take the shot.

Mostcamerasoffera collectionof

AF-pointselectionmodesthathelpyou

tochoosethepoint(s)youwanttouse.

Theseincludeoptionssuchassingle-

point,multiple-point,all-pointor

auto-point,zoneandtracking.The

smallertheselectionarea,themore

preciseyoucanbewiththefocusing.

However,if yoursubjectis moving,it’s

worthselectingmultiple-pointmodeor

zonemodeasit’seasiertokeepat least

partof a largerareaoverit.

In thepastI wouldhaveavoidedusing

anall-pointorauto-AFpointmodethat

putsthecamerain fullcontroloverwhich

AFpointis used(it alwaysjustfocusedon

thenearestormostcentralobject),but

Sony’srecentAFsystemshavechanged

that.ItsWideandZoneFocusArea

modesworkbrilliantlyandin continuous

autofocus (AF-C) mode in models like the

A6400andAlpha7 III,they’regreatfor

trackinga movingsubject.Butit’sworth

notingthattheyusuallytargetthenearest

partof thesubjectandif it stopsmoving,

it’spronetofocusingjustin frontof it.

Sony’sLock-onAFandReal-Time

Trackingmodesworkin a similarwayto

othermanufacturers’trackingmodes,but

arebetterthanmost.Youstartbyplacing

thepointoverthesubject,andthenpress

theshutterreleaseto activatethefocusing.

Onceyoustartshooting,thecamerais in

controloverwheretheAFpointgoes.It

usuallyfollowsthesubject,butif it strays

youhavetostopshootingtorepositionit.

MosttrackingAFmodesaren’tasfast

oraccurateasSony’s,butcanbeuseful

withslowerormotionlesssubjects.For

example,youcanplacethestartingAF

pointovera criticalpartof a subjectand

it should stay with it as you recompose.

Iliketofocusandrecompose–

isthisOK?

WhencamerashadoneAFpointweoftenhadto

focusandrecomposetheshotbeforetakingtheimage.

However,simpletrigonometrytellsusthatthiscanlead

tofocusingerrors.If you’reshootinga portraitwithan

85mmf/1.4lenswideopen,forexample,thedepthof

fieldis soshallowthatusingthecentralpointtofocus

ontheeyeandthenrecomposingcanresultin

theeyebrowornosebeingsharperthanthepupil.

Consequently,it’smuchbettertocomposetheshot

andusetheAFpointthat’s closest to the object you

want to be sharpest.

EyeAFcanhelpyou

nailthefocusing

witha widerange

of people shots

© MICHAEL TOPHAM

Neveruseauto-AFpointmode:true or false?

Whenshootinga portraitwideopenwithan85mmlensit’s

best to select an AF point rather than focus and recompose

A small AF point gives you precise control over the focus