计算机辅助光学设计codeVS2

1、3280 East Foothill BoulevardPasadena, California 91107 USA(626) 795-9101 Fax (626) 795-0184e-mail: World Wide Web: Section 2Digital Camera Design Study What is CODE V?A “power tool” for optical design and engineeringIncludes a wide range of technical features for:Creating models of diverse optical s

2、ystemsEvaluating optical performance in many ways, with tabular and graphical outputOptimizing the optical system with various error functions and constraintsPreparing for fabrication (tolerance analysis and more)Modern user interface gives quick access to all features, with a command and macro lang

3、uage available for advanced and custom applicationsInterface ElementsTitle BarNavigation WindowMenu BarToolbarLDM SpreadsheetCommand WindowCommand LinePlot WindowStatus BarTabbed Output WindowLDM and OptionsCODE V has two major levels, LDM and OptionsLDM is Lens Data Manager, where lens data is defi

4、ned and modifiedOptions are special calculations requiring multiple inputs, e.g., spot diagram, MTF, Automatic DesignThe LDM is operated from menus, tool bars, and dialog boxes (or from the command line)Options are launched from menus and controlled from tabbed dialog boxesEach option creates its ow

5、n tabbed output window (TOW)Option input can be modified or re-run from its TOW System Data and Surface DataLDM data is divided into two major categoriesSystem Data specifies overall properties such as f/number and wavelengthsSurface Data specifies any data that changes with surface number, from thi

6、ckness to decenters to tolerancesSystem Data is accessed through the Lens System data menu, which displays a multi-tabbed dialog boxSurface data is accessed from the LDM spreadsheet and from the Lens Surface Properties menuLDM spreadsheet displays basic dataSurface Properties dialog shows all data f

7、or a surfaceDigital Camera Design Study This section is based on the Digital Camera Objective example in the CODE V Introductory Users GuideWhat you will learn:Use the New Lens Wizard to select a patent lens as a starting point for a new designChange the System Data as needed for the new application

8、Work with system data, basic solves, lens drawings, surface data, scaling, MTF, and moreUse Optimization to improve the lensPerform Tolerance Analysis A similar problem will be posed as a workshop at the end of this section (solution script in the Appendix)Digital Camera Specs New Lens WizardThe New

9、 Lens Wizard (NLW) is designed to prompt you through the setup of a valid lens, using one of four sources: CODE V Sample LensesPatent Database (about 2400 lenses)Your own Favorites (which you can easily collect)A blank lensIn this case, we will use the patent database, making use of the “filter” cap

10、ability to narrow down the search based on the required specificationsRun the New Lens WizardChoose the File New menu to launch the NLW Click Next to clear the Welcome Screen Click the Patent Lens button, then click NextClick the Filter button to open the patent filter dialogFilter DialogCheck the i

11、tems of interest and enter min and max values for each, then click OK. F/# goal is 3.5 (try 1 to 4), Field of View goal is 26.5 (try 20 to 33), try 1 to 3 for number of elements.Note that this is actually the semi-field of view, which corresponds to object or image heightFilter ResultsThe filter ret

12、urns around 12 lenses Wider field and faster f/number than needed is bestThe triplet or02248 looks pretty good (f/2.4, 27.5)Click the Next button Note that each patent lens a lens drawing, and this one shows three defined field anglesDefining System DataSystem data defines the way the lens will work

13、 Required system data items are pupil size and wavelengthsThese plus field of view can be defined in the NLWMany additional system data values can be defined or modified through Lens System DataPupil definitionAs mentioned earlier, the pupil size sets the light-gathering power of the system and can

14、be defined in several waysWavelengthsAt least one wavelength must be defined, and up to 21 are allowed, always entered in nanometersField Definition“Field of View” (FOV) describes the size of the object or image that a lens can handle If the object is at infinity, angular measure is usedFor finite o

15、bject distances, object or image height can be used, with a slight preference for object-side definitionsCODE V performs calculations at discrete field points defined with the lensIn many cases, 3 field points are used, though some systems are designed for “axis only” with a single field Designers o

16、ften use additional field points for wider angle systems, and we will add an additional field point to this lensNLW Spec DataOn the Pupil page of the NLW, choose Image F/Number as the pupil spec and enter 3.5 as the valueOn the Wavelength page, enter 2 for the wavelength weight of the green (589.0)

17、wavelengthOn the Fields page, right-click on field 2 and choose Insert from the shortcut menuClick Next and on the last page, click Done.Enter 0, 11, 19, and 26.5 (degrees) for the Y Angle semi-FOV values of field points F1 to F4Titles and PicturesChoose the Lens System Data menuClick on System Sett

18、ings itemEnter new title, Dig Camera Intro SeminarClick the Quick 2D Labeled Plot icon to make a lens picture(Leave this window open for later re-draws)The LDM SpreadsheetThe LDM spreadsheet contains the basic surface dataSurface numbers, names (user labels), types, Y Radius of Curvature or Curvatur

19、e (depends on Edit Radius Mode setting), thickness (distance to next surface), glass name, refract mode (usually Refract or Reflect), aperture sizeRight click on any cell and choose Surface Properties to get more surface informationSurface DetailsValues in cells can be edited, including copy and pas

20、teThe status of a cell is indicated by a small status indicator (e.g., V for variable)You can change the status by right clicking and using the shortcut menuCells that are gray are defined indirectly (e.g., solves, default apertures, pickups) and cannot be editedYou can still right-click these value

21、s to change their statusRight-click on a cell and choose Surface Properties to see all information (e.g., right click on the thickness of surface 6, the gray cell with S for solve).Surface PropertiesFirst Order PropertiesThe required effective focal length (EFL) is 6mmTo display first order data inc

22、luding EFLChoose Display List Lens Data First Order DataCurrent value is 0.9528 mmThe Execute button updates the window You can also place EFL on the Status Bar for continuous updates (Tools Customize)Execute buttonScaling the LensSelect surfaces 1 to the image in the LDM spreadsheet Choose the Edit

23、 Scale menuNote that the surface range you selected is displayedIn the dialog box, click the Scale Effective Focal Length button, and enter the desired EFL (6.0) as the Scale Value, then click OK.Analyze DistortionDistortion is the variation of image height from the idea paraxial height, h = (EFL)*

24、(tan q) Click the Quick Field Plot toolbar buttonThe left curve is astigmatism vs. field angle, the right curve is distortion (about 0.2% maximum)EFLhqParaxial rayAnalyze MTFMTF is related to resolution or “sharpness” Choose Analysis Diffraction MTFFrequency 68 (cycles/mm) for maximum, 17 for increm

25、entOn Graphics tab, enter 68 for maximum plot frequencyClick OK - MTF is above 0.25 for all fields. Vignetting/IlluminationVignetting is the clipping of off-axis beams by apertures other than the stop Can be a problem or a solution (depends on specs)Non-zero vignetting reduces off-axis illuminationR

26、elative illumination includes vignetting effectsMTF text output includes relative illumination for each field (58.4% for the starting lens full-field)Other IssuesThis lens is very small with focal length and detector size around 6 mm (about 0.25 inch)The center element has a thickness of 0.126 mm, t

27、oo thin for practical fabrication Need to consider practical aspects of small elements, including thickness constraints in optimizationWould also need to to consider glass propertiesPatent lens has “fictitious” (variable) glass with high index of refractionHigher index glasses are more expensiveMay

28、want to constrain glass to lower index Workshop 2-1: Digital Camera 20Here are simplified specs for a digital camera with reduced field of view (something like a normal lens rather than wide angle as shown in text):F/number: 3.5Max semi-field of view: 20 degreesNumber of elements: 1 to 3Make sure th

29、e lens is defined for at least 3 visual wavelengthsFocal length 8.25 mm (Image height 3 mm)MTF 0.5 for all fields at 68 lp/mm (this will require optimization - see next problem)Distortion: less than 1% (+/-) full fieldNote: Use the New Lens Wizard patents to find a starting point (hint: use F/# 3 to

30、 5, FOV 20 to 25, number of elements 1 to 3, and % distortion 0 to 3 ). Scale, draw, and analyze as needed (minimum analysis: MTF and distortion). Save lens.OptimizationOptimization is used to improve the optical quality of a starting design Requires variables, parameters that can be alteredRequires

31、 an error function, a quantity that correlates with quality (smaller is better, zero is “perfect”)Requires constraints, or boundary conditionsCODE Vs optimization is called Automatic DesignUses a constrained damped least squares (DLS) methodProvides a sophisticated default error function and other i

32、ntelligent defaultsUser can re-define everything, including the error functionOptimization PlanUse LDM to define variables All curvatures, all thicknesses, all glassesDefine general constraints on thickness and glassDefine a specific constraint on EFL, others as neededDistortion may require a constr

33、aintDraw the lens at each cycleOptimize with default weightsAnalyze MTF and distortionRe-optimize with field weights adjusted to balance performance across fieldsDefine VariablesVariables are defined in LDM and saved with lens dataSelect one or more cells, right click, choose VaryRed V indicates a v

34、ariable (right click, Freeze to NOT vary)Vary radii of surfaces 1-6, thickness 1-5 plus imageDont vary thickness of 6 (it has a PIM solve)Glass will vary too (see next slides)Fictitious GlassIn CODE V, only fictitious glasses can be varied for optimizationFictitious glass is defined by its index (Nc

35、) at a central wavelength and its Abbe (V) value at two extreme wavelengths (typically d, F, & C wavelengths) V = (Nc-1)/(Ns NL)Two different formats are supportedNc:V (e.g., 1.5168:64.17)xxxxxx.yyyyyy Where:Nc = index at central wavelengthNs = index at short wavelengthNL = index at long wavelength

36、Dispersion = (Ns NL)Where:xxxxxx = (Nc-1) 1 Nc 2yyyyyy = V*10 10 V Variables & CouplingsAfter optimization, fictitious glasses can be converted to real glasses with the help of the CODE V sample macro GLASSFIT.SEQPre-AUTO LensThe LDM spreadsheet shows the values, variables, and paraxial image solve

37、Quick 2D Labeled Plot shows starting formVariables Ready for AUTOIts good to review your variables before optimization Choose the Review Variables and Coupling menuA “Coupling Code” of 0 means “vary,” while 100 means “freeze,” though frozen parameters are not shown in the review spreadsheet.Automati

38、c Design SettingsAutomatic Design is an incredibly flexible design toolRequires a ray-traceable starting lens with one or more variables (done in LDM) Provides several different built-in error functions, plus user-defined error functionsProvides many types of constraints to set requirements, plus us

39、er-defined constraintsRuns local optimization by default, but very effective Global Synthesis optimization can be used with a single clickInput dialog is divided into a number of tabs The Glass MapThe optimization glass map is defined on an index vs. dispersion (NF - NC) plotThe default glass map bo

40、undaries form a 4-sided polygon containing most real glasses with reasonable costDefault boundaries (RM p. 3-32)From sample macro VP_PLOT, boundaries added separatelyThe Glass MapMaking this a smaller 3-sided polygon can restrict variable glasses to a lower index region of generally less expensive g

41、lass typesUse SF2 to define the 3rd vertexGeneral Constraints TabGeneral constraints prevent non-physical solutions (e.g., negative edges, glass with n = 99) They apply to all surfaces and zoom positions, but can be overridden by specific constraintsEnter 0.9 for minimum center thickness, and 0.8 fo

42、r minimum edge thickness (others default)Delete glass SF4 and change Map 3 glass to SF2Specific ConstraintsSpecific constraints are boundary conditions imposed by you, to force the optimizer to maintain requirements Most common specific constraint is EFL or another scale-holding constraint, as shown

43、 in first exampleThere are many things you can constrain, divided into 8 categories (optical, manufacturing, real ray, etc.)Constraints can be held to a value (=), bounded ( or 10) tolerances Inverse vs. Sensitivity ModeSensitivity analysis means taking a set of assumed tolerance values and predicti

44、ng their performance effectsThis requires a way to determine the assumed tolerancesCould be based on fabrication capability (or guess work)Inverse sensitivity means determining tolerance values that cause a certain performance changeThis is done for each tolerance, scaling so that each tolerance cau

45、ses the same small drop in performanceLimits and rounding are applied to the values to make sure they are realistic, so in practice, not all tolerances will contribute the same error Default Tolerance Run InputTolerances are associated with surfaces and are thus defined in the LDM as part of lens da

46、taYou can define tolerances in great detail, for individual surfaces or groups of surfacesIf you run TOR without defining tolerances, a default set is defined for youIt includes all the basic surface tolerances plus group tolerances for single elements and cemented elementsThis is often a good start

47、ing point, but it does not contain group tolerances for non-cemented sub-assemblies, since CODE V does not know the mount structure of a lensPrepare the LensUse File Open or the NLW to locate and open the supplied lens cooke1.len (a Cooke triplet)Draw the lens with Display View lens or Place the len

48、s at best focus by clicking the Quick Best Focus button on the tool barTOR works best when the lens is at best focusQuick Best Focus runs the RMS Wave Error option and sets the image surface thickness for best focusRun MTF Tolerance AnalysisChoose Analysis Tolerancing MTFIn the dialog, enter 15 for

49、the Spatial Frequency for each of the three fields (Lines per MM column)Click OK. Tolerance OutputTOR generates significant output, including:Tolerance sensitivity tables for each field and zoom showing the performance change with compensated plus and minus tolerance changeA performance summary tabl

50、e for each fieldIf CODE V is determining the tolerance set (inverse sensitivity mode), two tables of tolerance values are printed (centered & decentered tolerances)A final 2-Sigma (98% probability) performance summary for all fields and zoomsA cumulative probability plotAll of this output will be co

51、vered in detail in the Introduction to Tolerancing sectionExample OutputPerformance Summary Table & GraphReview Tolerances (LDM)Special Features In this section, we will introduce two special features of CODE V: zoom and decentered systems CODE V has other special features, includingNon-spherical su

52、rfacesSolves and pickupsGradient-index (GRIN) materialsPolarizers and birefringent elementsDiffractive surfacesAs with decenters shown in this section, these features are accessed through Lens Surface Properties for required surfaceWhat is Zoom?Zoom actually means “multi-configuration” and is used f

53、or many situations where something changes in using the optical system, for example: Zoom lenses (air spaces change to change focal length)Scanners (tilt angles change to simulate scanning)Multi-spectral (spectrometers, demux systems, etc.)Zoom requires defining a nominal system, a number of positio

54、ns (up to 99), and the items that are “zoomed”Simultaneous optimization of multiple configurations is the most powerful feature of zoom in CODE VTilts & DecentersMany optical systems do not have an optical axis Surfaces or elements can be tilted or decenteredExamples: Fold mirrors, scanners, prismsC

55、ODE V defines a coordinate break which establishes a new local coordinate system for all following surfacesThe new coordinates are defined by x, y, and z decenters and by alpha, beta, and gamma Euler anglesThere are also special-purpose decenter types for fixed fold mirrors (“bend”) and for temporar

56、y tilts (“decenter and return” or DAR)A Simple ScannerScanners can be modeled in various ways Zoom is often used to vary the scan angleAn oscillating mirror can be modeled with two surfaces, one a zoomed DAR, the other a dummy with a fixed tilt angle (often 90 degrees)A Petzval lens can be turned into a scan lens by inserting a mirror and a dummy surfaceWe will first reduce the EPD to 20 mm and delete the two off-axis field pointsInsert scan mirror herePetzval Lens to Scanner (1)File New, New Lens Wizard, Sample LensesSelect cv_lens:petzval.lenEntrance pupil diameter 20, w