ch2-2 thin lens.ppt

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1、§3ThinLens（薄透镜）Atransparenthomogeneousmediumboundedbytwosphericalsurfacesisreferredtoasasphericallens.Ifthethicknessofsuchalens(shownasdinFig.2-3-1below)isveryshorterthanthatofobjectandimagedistances,andalsothanradiiofcurvatureofthesurfaces,thelensisreferredtoasathinsphericallens.Different

2、typesoflensesareshowninFig.2-3-2.Thelinejoiningthecentersofcurvatureofthesphericalrefractingsurfacesisrefractedtoastheaxisofthelens.Theseinterfacesaremostfrequentlysphericalsegmentsandareoftencoatedwiththindielectricfilmstocontroltheirtransmissionproperties.A1isveryclosetoA2,andbothofthemc

3、anberegardedasonepoint,thispointisdefinedastheopticalcenterO.QdA1A2CFig.2-3-1Q1Q'3.1thin-lensequationsReturntothediscussionofrefractionatasinglesphericalinterface,Let’slocatetheconjugatepointsforalensofindexnLsurroundedbyamediumofindexn1wherethelocationoftheconjugatepointsSandS′isgivenby（3

4、-1）writeonblackboardWeuseequation(3-1)againatthesecondrefractingsurface,wehave：（3-2）so（3-2）becomeas：（3-3）（3-1）＋（3-3）weget：(3-4)whereIfwedropthesubscriptsofS1andS'2intheequation(3-4),letSdenotesobjectdistanceandS'denotesimagedistance,(3-4)isrewrittenasIfthelensisthinenoughQdA1A2（3－5）shAccor

5、dingly,wehavetheveryusefulThin-LensEquation,Thisequationoftenreferredtoasthelensmaker’sFormulafrom（3－1）Ifsismovedawaytoinfinity,theimagedistances'becomesthefocallengthf'.（3-6）Byusing（3－2），（3－5）canberewrittenas：（3-8）WhichisthefamousGaussianLensFormula高斯公式。forthinlens（3-7）Thelenswhichhasreal

6、focalpoint（fandf’>0）isreferredtopositivelens(正透镜)，weknowfrom(3-6)thatthiskindlensrequires1/r1>1/r1dueto>1.Thelenswhichhasvirtuefocalpoint（fandf’<0）isreferredtonegativelens,thiskindlensrequires1/r1<1/r1dueto<1.ConverginglensDiverginglensMeniscusconvexPlanar-convexMeniscusconcavePlanar-conca

7、veBi-convexBi-concaveFig.2-3-2C2C1ABOOistheopticalcenter(光心)ofthelens.RayspassingthroughOmay,accordingly,bedrawnasstraightlinesduetonorefraction.Generally,severalbundlesofrayspassingthoughlensinanarrowconewillbefocusedonasphericalsegmentsurfaceσ.Sincetheraycon