专业英语第3讲

EnglishinOptoelectronicInformationTechnology,Chapter1GeometricalOptics,NewWordsFig.1.14(b)showsthemforadiverginglens.图1.14（a）描述了这些光线被一个会聚透镜折射；图1.14(b)描述了这些光线被一个发散透镜折射。Ineachcasethefocallengthofthelensandthedistancefromtheobjecttothecenterofthelens(theobjectdistance)determinethedistanceoftheimagefromthelens(theimagedistance).在每一种情况下，透镜的焦距和物体到透镜中心的距离（物距）决定了像到透镜的距离（像距）。,15,1.6LocatingImagesbyRayTracing,Althoughwecanusethesethreespecificraystolocatethepositionoftheimage,theactualformationoftheimageismuchmorecomplex.虽然我们可以用这三条特定的光线来定位所成像，但实际上该像的形成要复杂的多。Thelightfromeachpointontheobjectconvergestoformthecorrespondingpointontheimage.Raysfromasinglepointontheobjectstriketheentirelenssurface.物体上每一点的光线会聚形成像上相应的点。物体上一点发出的光线照射到整个透镜表面。Conversely,anysmallareaofthelenssurfaceisstruckbyrayscomingfromeverypointontheobject.相反地，透镜上任何一个小区域都被物体上每一点发出的光线照射到。,16,1.6LocatingImagesbyRayTracing,Alloftheraysstrikingeachsmallareaarefocusedtoformtheimage.Thus,theimageiscomposedofcontributionsoflightthatpassthrougheverypartoflens.照射到每一小区域的所有光线被聚焦来形成像。因此，像是由穿过透镜每一部分的光形成的。Forthisreason,blockingoutpartofthelensdoesnotcastashadowontheimage,butsimplyreducesthebrightnessoftheimageberestrictingtheamountoflightthatgetstoit.正因为这个原因，遮住透镜上的部分光线并不能在像上产生阴影，只不过是到达像的光线数量变少而导致了像的亮度减小。,17,1.6LocatingImagesbyRayTracing,Whentheraysareclosetoandnearlyparalleltotheaxis(theparaxialapproximation),asmallplanarobjectperpendiculartotheopticalaxisisimagedbyathinlensintoaplanarregionthatisalsoperpendiculartothataxis.当光线靠近光轴并且近似平行于它时（旁轴近似），垂直于光轴的物平面经薄透镜成像，其像也位于垂直于光轴的平面内。Thus,allpointsintheobjectplanearerepresentedaspointsinanimageplane.Whentheobjectisthree-dimensional,likethepencilinFig.1.14(a),pointslocatedindifferentobjectplanesdontfocusinasingleimageplane.这样，物平面内的所有点被像平面内的点来描述。当物体是三维的，如图1.14(a)中的铅笔，位于不同物平面内的点并不能聚焦在同一个像平面上。,18,1.6LocatingImagesbyRayTracing,Forinstructionalpurposeswerestrictourdiscussiontoplanarobjectsandtheirplanarimages.Thus,wenormallyrepresentobjectsandimageswithsimplearrowsperpendiculartotheopticalaxis.出于讲授目的，我们仅限于讨论平面物体和它们的平面像。因此，我们用垂直于光轴的简单箭头来标准地描述物体和像。Letusstatethegraphicalproceduretofollowforlocatingtheimagefromagivenlenswhenyouknowtheobjectsposition.在知道物体的位置的情况下，让我们列举一下定位由给定的透镜成的像的流程图。,19,1.6LocatingImagesbyRayTracing,Inthenextsection,wewilldescribehowtocalculatetheimageheightandlocationalgebraicallyfromthegraphicalraydiagram.YoushouldrefertobothpartsofFig.1.14asyoureadthesesteps.在下一节，我们将描述如何通过射线图用代数法计算像高和位置。当你读到这些步骤时，图1.14的两部分均会涉及到。A.Selectanappropriatescale(meters,centimeters,etc.)andmarkthepositionofthelensontheopticalaxis(alsoreferredtoastheprincipalaxis).选择适当的刻度（米，厘米，等），并且标定透镜在光轴（也作为主轴被提及）上的位置。,20,1.6LocatingImagesbyRayTracing,B.DrawalineLLthroughthecenterofthelensandperpendiculartotheopticalaxis,asshown.Thislinewillreplacetheactuallenssurfacesthatrefractthelight.B.如图，画一条穿过透镜中心并垂直于光轴的直线LL。这条直线将取代实际的透镜表面并可折射光线。C.MarkthefocalpointFofthelensontheopticalaxisandlocatetheobjectontheaxis,alltothesamescale.(Inproblemsofthissort,youwillordinarilybegiventhefocallengthfonthelens.)C.在光轴上标出焦点F，并用相同的刻度找出物体的位置。（对这类问题，一般会告诉你透镜的焦距f）,21,1.6LocatingImagesbyRayTracing,D.Drawthefollowingrays.Anytwooftheseraysaresufficienttolocatetheimage,butyoushouldalwaysdrawthethirdrayasacheck.D.画接下来的光线。任意两条光线便足以定位物体的像，但你总是会画第三条光线来作为检验。1.Drawray1paralleltotheopticalaxisfromtheobjecttothelineLL(thelens).Foraconverginglens,extendthisrayfromLLthroughthefocalpointonthesideoppositetheincidentlight.1.沿平行于光轴方向从物体画光线1到直线LL（透镜）。对于会聚透镜，从LL延长这条光线穿过入射光线另外一侧的焦点。Foradiverginglens,extendtherayfromLLasthoughtheraycamefromthefocalpointonthesamesideastheincidentlight.对于发散透镜，从LL延长这条光线好像光线是从入射光线一侧的焦点发出的。,22,1.6LocatingImagesbyRayTracing,2.Drawray2fromtheobjecttothelineLL,passingthroughafocalpoint.Foraconverginglens,drawray2throughthefocalpointonthesamesideastheincidentlight;从物体开始画光线2至直线LL，穿过焦距。对于会聚透镜，穿过入射光线一侧的焦点画光线2。foradiverginglens,drawray2inthedirectionofthefocalpointontheoppositeside.Inbothcases,continuetherayfromLLparalleltotheopticalaxis.对于发散透镜，沿另外一侧焦点的方向画光线2。这两种情况下，都是从LL沿平行于光轴的方向延续光线2。,23,1.6LocatingImagesbyRayTracing,3.Drawray3fromtheobjecttothelineLLatthecenterofthelensandcontinueitundeviated;从物体至直线LL画光线3，穿过透镜的中心，并且不发生偏折。E.Iftheraysconvergeonthesideoppsitetheincidentlight,theimageisrealandislocatedattheintersectionofthesethreerays.如果光线在入射光线的另一侧会聚，则像为实像并位于这三条光线交汇处。Iftheraysdiverge,theimageisvirtualandislocatedwherethesethreeraysappeartooriginate.Youcanmeasurethepositionandimageheightdirectlyfromthescaledrawing.如果光线是发散的，像为虚像并且位于这三条光线看起来发出的地方。你可以通过比例图直接测量出像的位置和像高。,24,1.6LocatingImagesbyRayTracing,Youcouldmakearaydiagramforeachpointontheobjecttofullylocatetheimage.你可以为该物体上的每一点都作一个射线图来定位它的像。However,ifalloftheobjectisatapproximatelythesamedistancefromthelens,thenyouneedonlyconsidertheimageofonepointoftheobjectandtherestoftheobjectistherebylocated.然而，如果物体上的所有点与透镜的距离都近似相等，那么，你只需考虑物体上一点的像，物体上其他点的像因此而定位。,25,1.6LocatingImagesbyRayTracing,Again,notethatforagivenobjectdistance,thesizeandpositionoftheimagearecompl