how to photograph a karate punch - rochester institute of … ·  · 2017-08-28microsoft word -...

HowtoPhotographthePowerofaPunch:usingpolarizedlighttoanalyzethedynamicsofkaratepunch.byTedKinsmanAssistantProfessorDepartmentofPhotographicSciencesRochesterInstituteofTechnologyJanuary12,2017Manymaterialsshowinternalstresswhenilluminatedwithpolarizedlightandphotographedwithasecondanalyzingpolarizer.Thisuniquepropertyofmaterialsiscalledbirefringence.Someofthemorecommonmaterialthatexhibitsthispropertyisglass,ice,andmostplastics.Tovisualizethepressurecreatedbyaprofessionalkaratepunch,Iusedablockofclearballisticsgelobtainedfromthesourceslistedbelow.Thesizeoftheclearballisticsgelis6by6inchesand16incheslong.ThegelatiniscalibratedtomeettheUSAFBIprotocolforballistictesting.IrealizedthatIhadtophotographaprofessionalpunchingtheblock.AricKeyes,alocalprofessionalKarateteacherknownforhisskillinthesport,volunteeredhisservices.Tophotographtheballisticgel,theblockwasilluminedbyanEinsteinflashoperatingat1/64thpower.Thereisasheetofplastictracingpaperplacedontheflashsideofthepolarizingfilmthatactsasadiffuser.Theblockofballisticsgelissmoothedwithaheatguntomakeitopticallyclear.Asecondpolarizerisplacedoverthelensofthecameratobetheanalyzingpolarizer.Withouttheanalyzeronthecamera,youwouldnotbeabletoobservethebirefringencecan.Iliketothinkofthesesystemsasapolarizingsandwichwherethemeatistheobjectshowingthestress,whilethebreadrepresentsthepolarizers.Torecordthehigh-speedaction,IusedaMumfordtimemachinetotriggertheflashatexactlythecorrecttime.Amicrophonetapedtotheballisticgeldetectedthepunch.ThesystemworkedsurprisinglywellandIwasabletoseetheuniquestresspatternsintheballisticgelproducedbyofdifferentpunches.SpecialthankstoAricKeyesofwww.kime-karate.comwhosystemicallyhittheblockofballisticgeltimeandtimeagain.

Asequenceoffourpunchesshownatdifferenttimings.

Equipmentsetup.Disadiffuser,P1isthefirstpolarizingsheet,P2istheanalyzingpolarizerandonthefarrightisthecamera.

Aprofessionalkaratepunch.Notetheevendistributionofforcethroughtheblockofballisticgelthatsimulatedhumantissue.PreformedbyAricKeyes.

Aprofessionalkarateknucklepunch.Notethedistributionofforceismuchdifferentfromthepunchshownabove.PreformedbyAricKeyes.

Anexampleofapunchperformedbyanuntrainedindividual.Theunevenangleoftheknucklesshowstheunevenpressureinthecontactarea.Theuseofballisticgelisanexcellenttechniqueforvisualizingproperpunchingtechnique.

Aheadbuttperformedbytheauthor.Thistypeofdefensiveblowisknownfordoingequaldamagetoeachoftheparticipants.Ahigh-speedvideorecordedwithanEdgertronichigh-speedvideocameracanbefoundat:

https://youtu.be/uzYmHuQxeesSources:ClearBallisticsGelhttps://www.clearballistics.com/PolarizingSheetRosco Polarizing #7300 Filter - 17x20" Sheet http://www.bhphotovideo.comEinsteinFlashE640https://www.paulcbuff.comMumfordTime-MachineCameraControllerhttp://www.bmumford.com/photo/camctlr.html