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An Overview of CCD Spatial Resolution - Andor Technology

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CCD arrays of over 1,000 x 1,000 sensors (1 Mega-pixel) are now commonplace in scientific cameras. The trend in cameras is for the sensor size to decrease, and ... PartoftheOxfordInstrumentsGroup Expand Collapse OxfordInstruments Applications Products News Events Contact en cn jp Investors Careers LifeScience CamerasEMCCDCamerassCMOSCamerasLowNoiseCCDCamerasSuper-ResolutionCamerasMulti-WavelengthImagingEx-DemoCameras ConfocalMicroscopyDragonflyConfocalMicroscopesBenchtopConfocalMicroscopesRevolutionUpgradesandWindows10MicroscopySolutionsPhotostimulationSolutionsIntegratedLaserEngineCryostatsforMicroscopy ControlSoftwareSolisPackagesSoftwareDevelopmentKitImageAnalysisSoftwareImarisPackagesImarisFreeTrialKomet MarketsCancerCellBiologyDevelopmentalBiologyNeuroscienceSingleMoleculeVirology   PhysicalScience CamerassCMOSCamerasEMCCDCamerasLargeCCDCamerasIntensifiedandGatedCamerasX-RayandNeutronCamerasSpectroscopyCamerasEx-DemoCameras SpectroscopySpectrographSolutionsDetectorsforUVtoNIRandSWIRSpectroscopyAccessoriesOpticalCryostatsOpticalCryostatsforSpectroscopyOpticalCryostatsforMicroscopy ControlSoftwareSolisPackagesSoftwareDevelopmentKit MarketsAdvancedMaterialsAstronomyBio-ScienceChemistryFluidMechanicsMetals,Alloys,Composites&CeramicsQuantumOpticsTomography   OEM PortfolioOEMRelationshipswithAndorScientificCamerasSpectroscopySolutionsSoftwareOpticalCryostatsMicroscopySolutions   Learning LEARNINGCENTREUpcomingWebinarsOn-DemandWebinarsMicroscopyTrainingCourseCaseStudiesApplicationNotesTechnicalArticles TOOLS AstronomyCalculatorCameraWindowSelectorHeliumCostCalculatorResolutionCalculatorSignaltoNoiseCalculatorThirdPartySoftwareCompatibility   Support ServiceandSupportSupportRequestRequestanewRMAFindaSupportCentreServiceProductsLiveAssist DownloadsSoftwareDownloadsDriversSoftware/UserManualsQuick-startGuidesCodeSnippets   News Events Contact eCommerce LearningCentre Asset AnEssentialOverviewofCCDSpatialResolution TheresolutionofaCCDisafunctionofthenumberofpixelsandtheirsizerelativetotheprojectedimage.CCDarraysofover1,000x1,000sensors(1Mega-pixel)arenowcommonplaceinscientificcameras.Thetrendincamerasisforthesensorsizetodecrease,andcameraswithpixelsassmallas4x4micronsarecurrentlyavailableintheconsumermarket.Beforeweconsiderthemostappropriatepixelsizeofaparticularapplication,itisimportanttoconsidertherelativesizeofprojectedimagetothepixelsizetoobtainasatisfactoryreproductionoftheimage. Consideraprojectedimageofacircularobjectthathasadiametersmallerthanapixel.Iftheimagefallsdirectlyinthecentreofapixelthenthecamerawillreproducetheobjectasasquareof1pixel.Eveniftheobjectisimagedontotheverticesof4pixelstheobjectwillstillbereproducedasasquareonlydimmer-notafaithfulreproduction.Ifthediameteroftheprojectedimageisequivalenttooneoreventwopixeldiagonalstheimagereproductionisstillnotafaithfulreproductionoftheobjectandcriticallyvariesonwhetherthecentreoftheimageprojectionfallsoneitherthecentreofapixeloratthevertexofpixels. Itisonlywhentheobjectimagecoversthreepixelsdowestarttoobtainanimagethatismorefaithfullyreproduced,andclearlyrepresentsacircularobject.Thequalityoftheimageisalsonowindependentofwheretheobjectimageiscentred,atapixelcentreoratthevertexofpixels.Nyquist'stheorem,whichstatesthatthefrequencyofthedigitalsampleshouldbetwicethatoftheanalogfrequency,istypicallycitedtorecommenda"samplingrate"of2pixelsrelativetotheobjectimagesize.TheNyquisttheoremdealswith2-dimensionalsignalssuchasaudioandelectricalsignalsanditisunsuitableforanimage,whichhasthreedimensionsofintensityversusxandyspatialdimensions. ModulationTransferFunction Inadditiontothediscretepixels,otherfactorssuchasthequalityoftheimagingsystemandcameranoisealllimittheaccuratereproductionofanobject.Theresolutionandperformanceofacamerawithinanopticalsystemcanbecharacterizedbyaquantityknownasthemodulationtransferfunction(MTF),whichisameasurementofthecameraandopticalsystem’sabilitytotransfercontrastfromthespecimentotheintermediateimageplaneataspecificresolution.Computationofthemodulationtransferfunctionisamechanismthatisoftenutilizedbyopticalmanufacturerstoincorporateresolutionandcontrastdataintoasinglespecification.Thisconceptisderivedfromstandardconventionsutilizedinelectricalengineeringthatrelatethedegreeofmodulationofanoutputsignaltoafunctionofthesignalfrequency. AtypicalMTFcurveforaCCDcamerawitha10x10and20x20micronpixelsisshownbelowright.Thespatialfrequencyofsinewavesprojectedontothesensorsurfaceisplottedontheabscissaandtheresultantmodulationpercentageontheordinate.Thelimitingresolutionisnormallydefinedasthe3percentmodulationlevel. Adequateresolutionofanobjectcanonlybeachievedifatleasttwosamplesaremadeforeachresolvableunit(manyinvestigatorspreferthreesamplesperresolvableunittoensuresufficientsampling).Inthecaseoftheepi-fluorescencemicroscope,theresolvableunitfromtheAbbediffractionlimitatawavelengthof550nanometersusinga1.25numericalaperturelensis0.27microns.Ifa100xobjectiveisemployed,theprojectedsizeofadiffraction-limitedspotonthefaceoftheCCDwouldbe27microns.Asensorsizeof13x13micronpixelswouldjustallowtheopticalandelectronicresolutiontobematched,witha9x9micronpixelpreferred.AlthoughsmallsensorsinaCCDimprovespatialresolution,theyalsolimitthedynamicrangeofthedevice. DiscovermoreinourLearningCentre. Date:N/A Author:Andor Category:TechnicalArticle Downloadaspdf Share Youhavesuccessfullyloggedout. Continue Openinanewtab

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