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视场光阑与孔径光阑doc
视场光阑与孔径光阑[doc]
ChapterVFieldstopandaperturestop
视场光阑与孔径光阑
5.1Fieldstopandaperturestop视场光阑与孔径光阑
5.2Filedofview视场
5.3Vignettingandfieldlens渐晕与场镜5.4Telecentricsystem远心系统5.5Depthoffocusanddepthoffield焦深与景深
5.6Straylightinlenses透镜中的杂散光
5.1Fieldstopandaperturestop
一、Fieldstopandaperturestop
Aperturestop:
Thestopclosetolenslimitsthesizeofthebundlesofraysofaxispoint.Itdeterminestheamountoflightreachinganygivenpointintheimage,thereforecontrolsthebrightnessofimage(imageplane).
Fieldstop:
Justfrontofthefocalplanelimitstheangleatwhichtheincidentbundlescangetthroughtothisplane(imageplane).Itdeterminestheextentoftheobjectorthefield.(Fieldstopisusuallymadetocoincidewithimage.)
二、Entrancepupilandexitpupil
EP:
Theimageofaperturestopformedbyprecedingit.
':
Theimageofaperturestopformedbyfollowingit.EP
PLTheimageofthisstop,asformedbythelensisfoundtolieattheposition.
''*Sinceisinsidethefocalplane,itsimageliesintheobjectspaceandisvirtualanderect,PLPL
PLcalledentrancepupil.
''*liesintheimagespace,calledexitpupil.PL
'''`*,,arepairsofconjugatedpoints.AnyrayintheobjectspacedirectedthroughoneofPPLLEE
thesepointswillafterrefractionpassthroughitsconjugatepointintheimagespace.
三、Chiefray
Anyrayintheobjectspacethatpassesthroughthecenterofentrancepupiliscalledchiefray.After
refractingalsopassthroughthecenteroftheexitpupil.*Chiefrayisacentralrayofobliquerays.
preliminarydesignofanopticalinstrument,mustdeterminewhichoneactuallydoesthelimiting?
ln
Theentrancepupilofthecentricsystemistheimageoftheaperturestopformedbyalllensespreceding
it.
Theexitpupilistheimageformedbyalllensesfollowingit.
四、Stopbetweentwolenses
Chiefraypassthroughtheentrancepupil,thestopandtheexitpupil.
Howtodetermineaperturestop?
五、Twolenseswithnostop
Theperipheryofanylensinsystemisapotentialstop.
Objectatinfinity,:
entrancepupil.MN11
''ObjectatA,:
entrancepupilPL22
Determinationoftheaperturestop
Thesystemconsistsoftowlensesandastop.'isthevirtualimageofthefirst()andastopformedby()lens1lens2LLP1212
':
VirtualimageofthestopPformedby.lens2P0
:
Virtualimageofthestopformedby.lens1P0
:
Virtualimageofthesecondlensformedby.lens1P21
ForallaxialobjectpointslyingtotheleftofX,limitstheentrancebundleofraystothesmallestP0angle.
constitutestheentrancepupil.P0
'constitutestheexitpupil.P0
'ForallaxialobjectpointlyingtotherightofZ,istheentrancepupilandistheexitpupil.PP212
Nominalaperturestop:
Theaperturestopofanysystemmaychangewithachangeintheobjectposition.
Generalrule:
theaperturestopofthesystemisdeterminedbythatstoporimageofstopwhichsubtendsthesmallestangleasseenfromtheobjectpoint.
Telescopeandmicroscope(lowpower):
usuallyaperturestopisselectedatthelarge-sizedobjectivelens.
5.2Fieldofview
一、Fieldofview
2W:
objectfieldandimagefield
Lookoutatlandscapethroughawindow.
Fig1:
Thefieldofviewislimitedbythesizeofwindowandbythepositionoftheeye.Windowisfieldstop.
Generalspeaking,fieldstopisatimageplane.(suchastelescope,microscope)Themarginofreticleorfilmisfieldstoporframe.
二、Fieldofaplanemirror
Thefieldofviewofferedbyaplanemirrorisverysimilartothatofasimplewindow.
'':
observer’seye,whichconstitutestheexitpupil.MN
:
Theentrancepupil,virtualimageoftheeyepupilformedbymirror.MN
Chiefraysdefinethefieldofview.
TheobjectBandentrancepupilMNareintheobjectspace.
三、Howcanyoudefinethefieldofviewofaconvexmirror?
四、Fieldofapositivelens
Thepupilofeyeisanexitpupilandaperturestop.
:
theimageofeyeisanentrancepupil.MN
Thefieldstopinthiscaseisthelensitself.
ABFPEObjectisinapositioninsidetheprimaryfocalpoint.Througheachofthreepoints、、
'L,raysaredrawnfromBtolens.
'''LRefractedraysaredirectedthroughP、E、,virtualimageislocatedatB.
*Whenconverginglensisusedasamagnifier,theeyeshouldbeplacedclosetothelens,sincethis
widenstheimage-fieldangle.
Forvisualvisionalopticalinstruments,theeyeshouldbeplacedtheexitpupilofopticalsystem,suchas
telescopesandmicroscopes.
五、Entrancewindowandexitwindow
Entrancewindowistheimageoffieldstoopformedbyalllensesprecedingit.
Exitwindowistheimageoffieldstoopformedbyalllensesfollowingit.
Bothentranceandexitwindowareatinfinity.六、ApertureangleandfieldangleApertureangle
:
Apertureangleintheobjectspace.On-axispointsubtendtothemarginofentrancepupil.u
':
Apertureangleintheimagespace.On-axisimagepointsubtendtothemarginofexitpupil.u
Fieldangle
:
Thecenterofentrancepupilsubtendedtothemarginofentrancewindow.w
':
Thecenterofexitpupilsubtendedtothemarginofexitwindow.w
5.3VignettingandFieldlens一、Vignetting
Atsmallfiledofview,thehighestandlowestrayspassingthroughthelens,strikethetopandbottom
'EPof,,.EPAS
Atgreaterfieldofview,entranceupperandlowerraysareoftenlimitedbythefrontandrearlensopenings.Thefailureofanobliquebeamisknownasvignetting.
Thebrightnessofanimagewillbegraduallydecreaseddarken,whenthefieldofviewincreased.
DwCoefficientofvignettingk,
D
Chiefray(principalray):
passesthroughthemiddleofaperturestopfromoff-axisobjectpointortheraythatentersthelensmidwaybetweenthehighestandlowestraysofobliquebeam.
二、Fieldlens
(1)Inordertoreducethesizeoffollowingopticalsystem,fieldlensisusuallyattheimageplane.
'(SeechapterI)ll,,,,01,
FreefromSSSCCIIIIIIIII
Thereareonlyfieldcurvatureanddistortioncausedby.SSSIVVIV
(2)Fieldlenscanbeusedtochangethepositionofexitpupiltosatisfypupilconnection.
Exitpupilofprecedingsystemshouldbecoincidewithentrancepupiloffollowingsystem.
IGalileantelescope
Aperturestop:
rimofobjectivesoisentrancepupilFieldstop:
eyepiecesoisexitwindow
IIKeplertelescope
reticleisfieldstop.
Entrancewindowandexitwindowareatinfinity.Fieldangle:
D,1tgw,',2f,1,D'2,tgw,',2f2,
'Exitpupiliscloseto.F2
ifeyeirisislessthanexitpupil,irisisaperturestop.IIIMicroscopewithlowmagnification
Aperturestopistherimofobjectivesoisentrancepupil.Fieldstopistherimofreticle.
Entrancewindowcoincideswithobjectplane.Exitwindowcoincidewithimageplane(infinity).
5.4TelecentricsystemIobjectspacetelecentricsystemIIimagespacetelecentricsystemIIIdoubletelecentricsystem
*Inmostcases,theaperturestopislocatedsomewhereinsidethelens,suchasphotographiccameras.
*eyepiecescondenserareexceptions.一、Telecentricsystem1)Telecentricsystemintheobjectspace:
'Theaperturestopisattherearfocalplane.F
Theenteringprincipalrayisparalleltoaxis.
2)Telecentricsystemintheimagespace:
FTheaperturestopisatthefrontfocus.Theenteringbeamcomefrominfinity,andexitingprincipalrayisparalleltoaxis.
3)Telecentricsystematthebothends:
''Theaperturestopisat.andarecoincided.FFFF2112
Thesystemusuallyusedasinvertingsystemandrelaylens.
二、Contourprojector
Contourorprofileprojectorisainstrumentforprojectingamagnifiedimageofasmallmechanicalpartstocheckitsdimensions.
,,,,1020505
Theopticalsystemisinvariabletelecentric,thevirtualofatelecentricsystemisthatthesizeoftheprojectedimagedoesnotalter,iftheimageisslightlyoutoffocus.
Thediameterofthelensaperturemustbegreaterthanthediameteroftheobject.
Condenserlensnearthelamp,providingcollimatedlight,mustalsobelargerthanthelargestobjecttobeprojected.
Finalimageisgenerallyprojectedonagroundglassscreen,sometimesequippedwithFresnellenstobrightenuptheouterpartsofscreen.
5.5Depthoffocusanddepthoffield
一、concept
Assumingthelensisfreefromallaberrations.
1)Therewillbeaceitainplaneintheobjectspacethatispreciselyconjugatetothefilmplaneinthe
imagespace.Thisisknownasthefocusedplaneintheobject.
2)Theobserver’seyeshavealimitedacuity.
Therewillbeasmallamountoftolerableblurinaphotographthatobserverwillbeunabletodistinguishitfromsharpimage.
apointobjectmaybeimagedasasmallcircleofconfusiononthefilm.,
Thedepthoffocusoflensisthedistancealongtheofsharpdefinitiontotheplanewheretheimageofapointsourcejustreachesthiscircleofconfusion.
Thedepthoffieldoflensisthecorrespondingdistanceofanobjectpointfromthefocusedplaneinobjectspacetotheplanewhereitsimagereachesthepermissiblecircleofconfusioninthefilmplane.
二、calculation
'1.DepthoffocusisobviouslyequaltotheproductofthediameterofthepermissiblecircleofC
confusiononthefilmandtheF-NumberFofthelens.
'f'''CNC,,*,*D
Thedistanceisthesamewhethertheimageisjustwithinorjustbeyondthe
filmplane.
'howlarge?
C,?
Whenapictureisviewedbyanobserver,mostpeopleareincapableofdistinguishingbetweenaperfectpointandasmallcircleofconfusionthatsubtendsabout2arc-min.
2.Thedepthoffield
Thediagramisbasedonthefactthateverythinglyinginthefocusedplanewillbeimagedsharplyonthe
fi