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16.PlanDenotesanobjectivelensthatproducesaat(planar)imagebycorrectingthesphericalaberration/curvatureoftheeldofanachromaticlensoranapochromaticlens.AllMitutoyoFSseriesobjectivesareplanapochromat.17.VignettingThisunwantedeffectisthereductionofanimage'sbrightnessorsaturationattheperipherycomparedtotheimagecenter.Maybecausedbyexternal(lenshood)orinternalfeatures(dimensionsofamulti-elementlens).18.FlareLensareistypicallyseenasseveralstarbursts,rings,orcirclesinarowacrosstheimageorview,causedbyunwantedimageformationmechanisms,suchasinternalreectionandscatteringoflight.19.DoubleImageAnimagedegradingaphenomenoninwhichanimageappearsasifitisadoubleimageduetoredundantlightprojectionandopticalinterferencewithintheopticalsystem.20.PupilDiameterandSpotDiameterofanObjective•PupildiameterDenotesthemaximumdiameterofaparallellightuxalongtheopticalaxisthatcanenteranobjectivefromtherear.Thepupildiameteriscalculatedaccordingtothefollowingexpression.PupildiameterObjectiveømm=2xN.A.xf1Glossary10.Bright-FieldIlluminationandDark-FieldIlluminationBright-eldilluminationdirectlylightsthespecimenwithasolidconeofraysandisthesimplestmethodavailable.Dark-eldilluminationusesahollowconeofraysformedbyanopaquestopatthecenterofthecondenserlargeenoughtopreventdirectlightfromenteringtheobjective.Thespecimenisplacedattheconcentrationofthelightcone,andisseenwithlightscatteredordiffractedbyit,thereforescratchesanddentsonthespecimensurfaceareilluminatedwhiletherestremainsdark.11.ApochromaticObjectiveandAchromaticObjectiveAnapochromaticobjectiveiscorrectedforchromaticaberrationatthered,greenandbluewavelengths.Anachromaticobjectiveiscorrectedforchromaticaberrationattheredandbluewavelengthsonly.12.KoehlerIlluminationKöhlerilluminationovercomesthedisadvantagesofotherschemesbycausingparallelraystolightthespecimensothat,becausetheywillnotbeinfocus,theimageofthespecimenwillnotincludeanimageofthelightsource.ImagingsystemRelaylensFieldstopAperturediaphragmCondenserlensFiber-opticcableBeamsplitter95Illuminatedfieldofview13.TelecentricIlluminationThisilluminatingopticalsystemisdesignedsothatprincipallightpassesthroughthefocalpoint.Thissystemhastheadvantageofretainingthesizeoftheimagecenterevenifitisoutoffocus(althoughthecircumferenceoftheimageisdefocused).Thisilluminationsystemprovidesanevenilluminationintensityovertheentireeldofview.14.ApertureDiaphragmThisdiaphragmadjuststheamountoflightpassingthroughandisrelatedtothebrightnessandresolvingpowerofanopticalsystem.Thisdiaphragmisespeciallyusefulinwidthdimensionmeasurementofcylindricalobjectswithcontourillumination,andprovidesthehighestdegreeofcorrectmeasurement/observationbysuppressingdiffractioninanoptimalaperture.15.FieldStopThisdiaphragmisusedforblockingoutunwantedlightandtherebypreventingitfromdegradingtheimage.Beamspotdiameter•SpotdiameterIfabeamoflightwithauniformlydistributedintensityentersanobjectivefromtherear,thebeamisfocusedtoaspotofnitesize.Thissizeisknownasthespotdiameter.Theapproximatevalueofaspotdiameteriscalculatedfromthefollowingexpression.øµm=1.22xλN.A.However,theaboveexpressioncannotbeappliedifthelightsourceisalaserbeamofwhichtheintensityformsaGaussiandistributiononthecrosssection.Thediameterofalaserbeamisgenerallyindicatedby1/e2ofthepeakvalue,i.e.13.5%ofthepeakvalue.Thespotdiameterofalaserbeamiscalculatedfromthefollowingexpression.øµm=4xλxfπxD(whereλisinµm;fandDareinmm)7-29
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