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1、Projectorusuallyisusedtoprojectimageononescreenfarawayfromprojector.Thedistances′fromthescreentolensofprojectorislongerthanthefocaldistance,theslide(幻灯片)alwayslocatesclosetofocalplane,inthiscase,wehave§4OpticalInstruments4.1projector(投影仪)Here,thetrans
2、versemagnificationisdirectlyproportionaltotheimagedistance,theimageisrealandupsidedown.LightsourceConvexlensProjectionlens幕ABCPQR4.2CameraComparingwithprojector,camerainstructureisincontrary.s>>f,s'≈f.Incamerasystem,thereusuallyisadiaphragmbesidessome
3、lens.Thefunctionofdiaphragm(光阑)：1.controlilluminanceonthefilm,ortimeofexposure.2.controldepthoffield.depthoffield(景深):Whenthediaphragmisfixed,iftheimagepointorspeckleonfilmformedbyobjectpointattheplaneΠissmallest,theimagespeckleonfilmformedbyobjectpoi
4、ntattheplaneAorBislagerbutstillsmallerthantheminimumsizeresolvedbythefilm.Therangeδxisdepthoffield.filmδx′ΠδxABTheluminance(亮度)ofimagedependonthefocallengthanddiameteroflens.SotheintensityofimageisproportionaltotheareaoflensorD2，wehavetherelations：强度是
5、胶片上单位面积接收到光功率的量度，而像的面积正比于Whentheaperture(光阑,diaphragm光圈) becomessmall,thebeamgoingthroughtheapertureapproachesthin, thusthespotonfilmbecomessmallerand depthoffield(景深)increase.Besidesdiaphragm,thefocallengthandobjectdistancealsoaffectthedepthoffield,w
6、hentheobjectdistancechangesδx,imagedistancechangesδx',thesmallertheδx'/δxratio,thebettertheincreaseofthedepthoffield.FromtheNewtonformulaδx'/δx=-f2/x2weknowthat,foragivenfocallengthf,thesmallerthex,thesmallerthedepthoffield.sowhenwetakeaphotosofobject
7、snotfarawayfromus,wecangetclearimageofobjectslocatedbeyond.Whiletakingphotosforobjectsnearthecamera,wecangetclearphotosforaobjectslittlefarther.ρistransmissioncoefficient(透射系数)，theilluminanceontheimageisproportionaltothesquareofrelativeaperture.例：写成的物
8、镜在像面上所生的光照度较相对孔径（）高一倍；比高一倍；比又高一倍。WedefineRelativeaperture(相对孔径):D/fTheIlluminance(光照度)ofimageonthefocalscreenofcamerawiththerelativeapertureD/fis：HereBisluminance(亮度）ofobject.4.3StructureoftheHumanEyeThehumaneyecanbethoughtofasapositivedouble-
