国外权威摄影杂志The Ultimate Beginners Introduction to Exposure.docx

国外权威摄影杂志The Ultimate Beginners Introduction to Exposure.docx

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国外权威摄影杂志TheUltimateBeginnersIntroductiontoExposure

odaywe’llbewalkingthroughtheconceptofexposure,rightfromthebeginning.Thisarticlewon’tbefuddleyouwithcomplicatednumbersandjargon,butitwillhelpyoufeelmoreconfidentwithyourphotographyandunderstandacoreconceptthat’savitalpieceofthephotographyjigsaw.

Preface

Ibelievetherearethreedifferenttypesofphotographers:

technical,artistic,andthosethathavegoodartisticvisionandcombinestechnicalknowledgetoachievethatvision.Noneisrightorwrong.Allarejustdifferentinapproachandexecution.

ThefirstphotographerIevermentoredwasanamazinglyartisticwoman.Shehadaknackforseeingthingslikeno-onehadeverseen.Shewasalsoavoraciouslearnerandsheaskedmeforhelponthetechnicalsideofthingstomakeherselfbetter.

Istartedspoutingallthenumbers,allthetheories,andallthescience.Theresponse?

“Whoa,Myminddoesn’tthinkthatway”.Andshewasright.Peoplewhoareveryartisticthinkdifferently,theirbrainscomputethingsdifferentlythansomeonethatthinksmoreanalyticallyandscientifically.

Ineededtochangemyteachingmethodstofitthewayshethinks.SothatiswhatIwilldowiththisarticle–explainthetechnologywithoutthemathandnumbersandtheories.

Bytheway,thatstudentisnowoneofthetopportraitphotographersinherstate（heck,Ithinkeverywhere）andIcouldn’tbemoreproudofher.Sheinspiresmeeveryday.

TheTriangleofExposure

Therearethreemainingredientstogoodexposure:

Aperture,ShutterSpeed,andISO.Okay,yesIsaidnomath,butIwilluseabitofgeometrytoillustratetheeffectthatthethreecomponentsofexposurehaveoneachother.IamcertainlynotthefirsttothinkofthisasatrianglebutIdothinkitisthebestrepresentation

Thinkofaperfectexposureasaperfecttriangle–alltheanglesareequal,allthesidesareequal.Nowifyouchangejustonepartofthatexposureortriangle,itisnolongerperfectsoyouwillneedtochangeanotherpointoftheexposureortriangleanequalbutoppositeamounttomakethattriangleandthereforetheexposureperfectagain

Asyoucansee,alltheelementsofexposurehaveaneffectontheothers–sowiththatinmindweneedtoknowthehowsandwhysofallthedifferentelementstobestunderstandhowtogetbothagoodexposureandthedesiredresultsinourphotographs.

Nowyoumayask;“Whydoweneedtohavealldifferentsettingsforexposure.Whyisn’ttherejustone?

”Well,inthelastcenturyonalmostallofthepointandshootcameras,that’sthewayitwas.Theaperturewasfixed,aswastheshutterspeedand–eventhoughyoucouldbuyfilmthatwasdifferentISOs–therewasusuallyonlyonerecommendedforthatparticularcamera.Butitwasverylimiting.

Sincethosecameraweresetupforanaveragescene,youeithershotanormaldaylightsceneor（ifyoupoppedonaflash）anindoorscene.Forgetaboutshootinganaturallightsunsetornightshot.Forgetaboutstoppingactionofaracecar.Youwerestuckwithwhatyouhad.

Nowwewanttobemoreartisticinourphotosandwewantmorecontroloverwhatweshoot.Sotoachievethatartisticandtechnicalcontrol,weneedtoknowaboutthedifferentsettingswecanuseandwhyweusethem.

Solet’sstartwithAperture

Aperture

Apertureisacircularopening（somewhat）inourlensthatisadjustablefromaverysmallcircletoalmostaslargeasthelensitself.Weadjustittoletmoreorlesslighthitthedigitalsensororfilm.Thinkofwindowblindsasyouraperture,andthewallinyourroomoppositetheblindsisyoursensororfilm.Asweopentheblinds,morelightcomesthroughandwecanseethewallbehindusgetbrighterandbrighter

Likewise,asweopenuptheapertureonourlens,wegetmorelightonoursensororfilm.

TheopeningofourlensorApertureisexpressedinfstopsandhereisaverytypicalrangeoffstops:

Youmaysay;nowwaitaminute,whydothelargestopeningshavethesmallestnumbers?

Well,thinkofitthisway;imaginethenumberasthebottomnumberofafraction.Soifwehavef4thatwouldbe1/4andf8wouldbe1/8and1/4islargerthan1/8.Okay?

Okay.

TheAperturenumbersIhaveaboverepresent“WholeSteps”oflightfromonetothenext.Whatisawholestep?

Awholesteprepresentsthedoublingorhalvingofthelightthroughthelens.Sof1.4willletintwiceasmuchlightasf2.0.f2.0twiceasmuchlightasf2.8orwecanalsosaythatf2.8ishalfasmuchlightasf2.0.

Onyourlens,youmayseenumbersinbetweenthenumbersabove.Thoserepresenteither1/3orΩstops（dependingonyourcameramodel）sowecanfinetunebeyondjustwholestops.

Sowehaveallthesedifferentaperturesavailabletoletindifferentamountsoflight.WhyshouldIcareandwhyshouldchooseoneovertheother?

Thisiswheretheartistsidecomesin–tohelpmakethosedecisions.ThefollowingaredifferentartisticstyleswecanuseandthedifferentpartsofanimagethatApertureeffects.

DepthofField

Whenwelookatanimage,thereisapartthatisinperfectfocusandthentherearepartsthatbegintobeoutoftherangeoffocus.YoucanhaveasmallDepthofField（DOF）whereonlyyoursubjectisinfocus,oryoucanhaveadeepDepthofFieldwherepracticallyeverythingisinfocus–orreallyanywhereinbetween.

Depthoffieldisdeterminedbythreethings;aperture（fstop）,distancetoyoursubject,andlensfocallength（50mm,200metc）,withAperturehavingaprofoundeffectonDOF.Let’sseewhatanimagelookslikejustvaryingtheapertureandleavingalonetheothertwoparts:

Photographersthatshootportraitsusuallyuselargerapertures（lownumbers）forashallowDOFtohighlightandisolatetheirsubjects.LandscapephotographersusuallyusesmallaperturestohaveaverydeepDOF,allthewayfromtheforegroundtothebackground.

Asusual,thereareexceptionstotheserulesandthatisruledbythephotographer’sartisticideasandvision.

ShootinginLowLight

Aswesawwiththewindowblindsexample,openingupourapertureallowsmorelighttohitoursensororfilm.Sowhenshootinginlowlight,itmayhelptoopenupyouraperturetomakeiteasieronourothertwosidesoftheexposuretrianglewhichIwillexplainmorelaterinthosesectionsonShutterspeedandISO.

ShutterSpeed

Shutterspeedcontrolshowlongthelightcomesthroughouraperturetoourdigitalsensororfilm.Thelongerthetime,themorelightwillhittheirsurface.Thatistechnicallywhatshutterspeeddoes.

Artistically,shutterspeedcontrolsmotion.Whetherwewanttofreezemotionorshowmotion,shutterspeedistheportionofexposurethatwillcontrolthataspect.

Shutterspeedsareexpressedinfractionofasecond1/8,1/125,1/1000etc.butinmostmoderndigitalcamerasyoumaynotseethe1/expressed（buttheystillarefraction）.Youmostlikelyseetheaboveexpressedas8,125,1000etc.

Thefirstconsiderationwehavetothinkaboutis:

canwehand-holdthecameraatthisshutterspeedandnothavetheslightmovementofthecamerashowupinourimagemakingitblurryorlesssharp?

Mostpeopleareabletohandholdacameraintherangeof1/60thto1/200thwithanormallenson.Whenyouusetelephotolensesyoumayneedtouseafastershutterspeed.

Acommonruleofthumbthesedaysistotakeyourfocallengthofyourlensandshootatleastasfastasthat.Ifyouhavea300mmtelephotolens,yourminimumshutterspeedshouldbe300（1/300or1/320asiscommon）Ifyoucannothand-hold,youmustuseatripod.

Beyondthatwecannowmakeanartisticjudgment–dowewanttostopaction,orshowmovement?

Andthisisajudgmentyouneedtomake.Sometimeswemaywanttofreezeoursubjectandkeepitsharpandclear.Othertimeswewantsomebluronthesubjecttogivetheviewertheimpressionthattheobjectismovingorisatspeed.

Inthisimageofthetrolleydowntown,inthefirstexampleweusedahighshutterspeedtostopthetrolleyasitmovedpastthebuildings（whichmaybewhatwewant）.Butdoestheviewerreallyknowifthetrolleywasmovingpastorjuststoppedatthestation?

Inthesecondexampleweslowedtheshutterspeedwaydownto.3（3/10th）ofasecond.Nowtheviewercantellthatthetrolleyismovingatspeedpastthebuilding.

Againthisisthedecision you havetomake.Whatdoyouwanttoconvey?

Otherexamplesofusingahighshutterspeedtostopaction:

Stoppingtheflightofajetasitfliesby,oracarathighspeed.Freezingtheswingofthebatofabaseballplayer,ahighdiverinmidarcabovethewater.Againyouwoulduseahighshutterspeedtofreezethemovementoraction.

Intheimagebelow,aslowshutterspeedwasused（onatripod）tosilkenthewaterandshowmotion.Thesamecanbedoneforawaterfall,anoceanorafountain.

ISO

ISOisthesensitivitytolightofthesensororfilm.Thehigherthesensitivity,thelesstime（shutterspeed）orthelessamountoflight（aperture）needstohitthesensorforthecorrectexposure.Itisadjustableinmostcameras,inarangeofabout200to1600.Highendcamerascangowaybeyondthat.

WeuseISOtohelpusachievewhatwewanttodowiththeothertwosidesofexposure;ApertureandShutterSpeed.Youmayask;Whydon’twejustusethemostsensitiveoneandforgetaboutit?

WellbecausethedownsideofhigherISOisthatitincreasesthenoiseorgraininourimages.Thiscansometimesmaketheimagelooksobadthatitbecomesunusable（oratleastun-printableatadecentsize）.

SoourobjectiveistousethelowestISOpossible,butbalancingthattowhatwewanttoachieve.

Shootingoutdoorsonsunnyorevenslightlyovercastdayswe