MIT 2.71/2.71009/28/05 wk4-b-1Imaging Instruments (part I)• Review: Principal Planes and Focal Lengths • the Numerical Aperture and f/#• Pupils & Windows; Apertures & StopsMIT 2.71/2.71009/28/05 wk4-b-2Focal Lengths & Principal PlanesEFL: Effective Focal Length (or simply “focal length”)FFL: Front Focal LengthBFL: Back Focal LengthFP: Focal Point/Plane PS: Principal Surface/Planegeneralized optical system(e.g. thick lens,multi-element system)2ndPS1stPS2ndFP1stFPEFLBFLFFLEFLMIT 2.71/2.71009/28/05 wk4-b-3The significance of principal planesmulti-elementoptical system2ndPS2ndFP1stFP1stPSobjectss’,111fss=′+ssm′−=lateralhold, where f = (EFL)MIT 2.71/2.71009/28/05 wk4-b-4Numerical Aperturemedium ofrefr. index nθθ: half-angle subtended by the imaging system from an axial objectNumerical Aperture(NA) = n sinθSpeed (f/#)=1/2(NA)pronounced f-number, e.g.f/8 means (f/#)=8.Aperture stopthe physical element whichlimits the angle of acceptance of the imaging systemMIT 2.71/2.71009/28/05 wk4-b-5Aperture / NA: physical meaningmedium ofrefr. index nθThe Numerical Aperturelimits the optical energythat can flow through the systemLater we will also learn that the NA also defines the resolution (or resolving power) of the optical systemMIT 2.71/2.71009/28/05 wk4-b-6Entrance & exit pupilsmulti-elementoptical systemimage throughpreceding elementsimage throughsucceeding elementsentrancepupilexitpupilMIT 2.71/2.71009/28/05 wk4-b-7The Chief RayStarts from off-axis object,Goes through the center of the ApertureMIT 2.71/2.71009/28/05 wk4-b-8The Field StopLimits the angular acceptanceof Chief RaysMIT 2.71/2.71009/28/05 wk4-b-9Entrance & Exit Windowsmulti-elementoptical systemimage throughpreceding elementsentrancewindowexitwindowimage throughsucceeding elementsMIT 2.71/2.71009/28/05 wk4-b-10All togetherentrancepupilexitpupilexitwindowentrancewindowfieldstopaperturestopMIT 2.71/2.71009/28/05 wk4-b-11All togetherentrancepupilexitwindowentrancewindowfieldstopaperturestopexitpupilMIT 2.71/2.71009/28/05 wk4-b-12Example: single-lens cameraobjectplaneimageplane2ndFP1stFPsize offilmor digitaldetectorarrayMIT 2.71/2.71009/28/05 wk4-b-13Example: single-lens cameraobjectplaneimageplane2ndFP1stFPApertureStop& EntrancePupilMIT 2.71/2.71009/28/05 wk4-b-14Example: single-lens cameraobjectplaneimageplane2ndFP1stFPExitpupil(virtual)ApertureStop& EntrancePupilMIT 2.71/2.71009/28/05 wk4-b-15Example: single-lens cameraobjectplaneField Stop& Exit Window2ndFP1stFPchief rayMIT 2.71/2.71009/28/05 wk4-b-16Example: single-lens cameraField Stop& Exit Window2ndFP1stFPchief rayEntranceWindowMIT 2.71/2.71009/28/05 wk4-b-17Example: single-lens cameraField Stop& Exit Window2ndFP1stFPExitpupil(virtual)ApertureStop& EntrancePupilEntranceWindowMIT 2.71/2.71009/28/05 wk4-b-18Example: single-lens cameraField Stop& Exit Window2ndFP1stFPExitpupil(virtual)ApertureStop& EntrancePupilEntranceWindowMIT 2.71/2.71009/28/05 wk4-b-19Example: single-lens
View Full Document
Unlocking...