Phys 462 – Lab Session 6
Contents
1. ASTIGMATISM LONGITUDINAL CHROMATIC S x T mm SPHERICAL ABER mm FOCAL SHIFT mm T7 Pe tos 0 5 Oi pee hacia SE sj Y iit DISTORTION X 153 5 1 4 donet AXIS 2 mm E ve LATERAL COLOR mm ime a 0 2 1g m aa A O Sede e a Jon 7 UNITS m SCENA D OUR EFL 1 24e 03 PT Toe BUSY o Ey t0 1 24e 03mm v ar WAVELGTH 0 588 2 0 486 0 0 656 um RAY TRACE ANALYSIS 01 48 AM FULL FIELD 0 5deg 0 7 FIELD 0 55deg ON AXIS Odeg 0 05 0 0 05 0 1 FOCUS SHIFT SPOT SIZE amp FOCUS SHIFT UNITS mm PHYS462 Lousy Telescope Conde whee UE dani SPOT DIAGRAM ANALYSIS SRM 16 Jj xi LAM 2 50 T du 4 40 N e qus E u 30 2 0 8r 4 20 0 4 Pp 5 0 080 0 2 0 4 0 6 0 8 O Fractional Object Height FBY Monochromatic wv1 0 5876um PHYS462 Lousy Telescope SPOT SIZE amp OPD vs FIELD Conde Now try optimizing it use the GENII error function once more Turn off the auto focus of the image screen set its thickness to zero We will force the optimizer to focus the image right there Now keep pressing the optimize button gt until the configuration converges to a stable solution The result that got was PHYS462 Lousy Telescope UNITS MM FOCAL LENGTH 834 6 NA 0 1078 DES Conde 153 m n SSS The resulting ray cr2. This is an ultra wide angle lens that may potentially be suitable for a large format film camera such as a Hasselblad or a Mamiya However it includes only four lens elements and my initial design was done using my own intuition without any computer optimization Look at the ray fans heading toward the final image plane Their behavior is perfectly suitable for illuminating a planar detector there such as a piece of film or a simple viewing screen But these rays might be difficult to pass through any additional optical relay stage that we might contemplate placing behind this lens Why is that What geometry would we prefer for the emerging ray pencils if we did need to put some relay optics behind this wide angle lens Recall that by right clicking the graphics windows and choosing copy to clipboard you can copy the graphics for subsequent pasting into a word document You can then use these diagrams in your lab report Initial evaluation Now invoke the Evaluate gt Paraxial Setup and Evaluate gt Paraxial Ray Analysis options from the menu bar of the main OSLO window These functions produce their output as tabular text it is sent to an OSLO text window Use these functions to determine the following quantities for inclusion in your lab report e The f of the lens e The location of the cardinal points fo fe hy and ho e The entrance and exit pupil locations and sizes e The effective focal length e
3. angle 75 000000 Primary wavin 0 587560 RADIUS THICKNESS APERTURE RADIUS GLASS SPECIAL 0 000000 1 0000e 20 2 3 7321e 20 AR Lg Lx 60 o00000 2 1 000000 J 25 000000 K N 8K7 o Ey L2 13 88888s9 2 1 130809 W 25 000000 P Am cd Lg L3 19 2307689 2 1 000000 7 10 000000 K N 8k7 P J ESS Ss 6 739979 16 676983 v 10 000000 CX AR iz Ast 1 0892e 03 W 3 719642 5 3 000000 A srio ce LJ Ee 16 439319 0 593228 V 9 000000 PK arD fg zz 21 007861 WJ 11 170577 S 15 000000 2 srio PY E 61 067432 W 0 000000 2 15 000000 Py ari fog 0 000000 11 274063 2 60 000000 2 i y The OSLO manual describes the GENII error function as follows The GENII error function so called because it was originally used in the GENII program uses multiple items of data from each traced ray to build a compact error function that is well suited to interactive design lt uses only 9 10 rays to derive a 31 term error function that makes use of the relationships between classical aberrations and exact ray data The individual terms are normalized so that a value of 1 0 represents a normal tolerance for the term making it easy to see the significant defects in a design and apply appropriate weighting if necessary The user only needs to specify the spatial frequency at which the system is to be optimized which makes it easy to use The GENII error function is designed to handle systems
4. A 9 000000 15 000000 2 15 000000 P 60 000000 2 GLASS SPECIAL AIR 1 N 8k7 AIR J N amp k7 PJ AIR J sFio pes Air sr10 P Reflect ar Reflect hatch Pickup P Catalog C D Model M Direct Having done this you can now create sliders to adjust the refractive index and dispersion of the glass material Note that have designated the glass materials for surfaces 5 and 7 as pickups of surfaces 1 and 3 respectively This simply forces surfaces 5 and 7 to always use the same material as are assigned to surfaces 1 and 3 You may wish to see if you can get any benefit from allowing all four elements to have their own independent choice of glass Warning There are a lot of free parameters that you can adjust here 8 curvatures 7 thicknesses and 8 glass parameters You must make frequent and independent snapshot copies of your current design as you work It is very easy to get lost and to wander far from a useful lens design Try to see if you can understand what happens as each parameter is adjusted Are there some parameters whose effects complement each other If so can you improve the performance by trading these against each other What are the design tradeoffs that you are encountering What are some of the things that can go dramatically wrong If you were getting your lens manufactured for which design elements would you need to specify the tightest tolerances What hap
5. scale where there is a space between each argument Each of the quantities in angle brackets should be replaced by a value of your choosing as follows e nraysis the number of rays in the spot diagram 50 works well e defocus Is the distance inside and outside of focus to sample e nposis the number of defocused positions to try each side of best focus e scale is the horizontal scale in mm for plotting the spot diagrams You should immediately see that there are some significant aberrations Examine the spot diagrams copy some relevant examples and write a few sentences describing of what you see to be included in your report Based on the spot sizes in the image plane what would be the smallest angular displacement that could be resolved by this lens in the object space Now click the setup window toolbar button and select Ray analysis You should obtain a window something like this Field 75 deg 1mm ASTIGMATISM LONGITUDINAL CHROMATIC Sx T m SPHERICAL ABER mm FOCAL SHIFT mm 710 7 t X1 A N N RM i i 4 ee SS x k X a NUN NT y Y 5 2 Prop 55 4 403 CR NR a y DISTORTION X ASS ES 100 ES aK E AXIS CR 1 100 LATERAL COLOR mm 0 2 A NM 0 2 0 E SMAGE NAT 0 B6B EFL 9 51 SA pura pc Angle rers Q8 Mar 07 G t Da 9 51mm D E ar WAVELGTH 0 588 4 0 486 5 0 656 u
6. in some of the elements What effect does this have If you ambitious you can try getting OSLO to choose the best glass for one of the lenses found it did ok choosing a glass for the third lens e OSLO does not do a good job of automatically optimizing the curvatures or thicknesses of the front two lenses But you can change one or other of these and let OSLO choose the best way re optimize the rest of the lens to account for your change Optimization of a telescope As another example try optimizing the telescope system that have provided named Phys462_lab6_poor_telescope len i e 14 PHYS462 Lousy lelescope UNITS MM FOCAL LENGTH 1242 NA 0 07246 DES Conde al CA This is a starting point for a telescope but as you will see it too has its problems It is setup for eyepiece projection of a scene at o onto a screen behind the Ramsden eyepiece This arrangement is commonly used by amateur astronomers to project an image from their telescope onto the sensor plane of an SLR camera have set the field angle for the source to be 0 5 which makes the full field about twice the size of the full moon Examine the ray crossing plots and spot diagrams for the image screen set for auto focus at minimum spot size They should appear as below What aberrations do you see 15 Field 0 5 deg 2 mm
7. 5 FOCUS SHIFT SPOT SIZE amp FOCUS SHIFT UNITS mm UAF Phys452 Wide Angle lens Merk Conde s 0 486 War 0 858 SPOT DIAGRAM ANALYSIS de AM 0 5 20 04r 16 1 7 _ zU 0 3 412 y v2 o ir 2 0 2 48 13 O 1k 44 l l l l 0 0 0 2 0 4 0 6 0 8 1 0 Fractional Object Height FBY Monochromatic wv1 0 5876um UAF Phys452 Wide Angle lens SPOT SIZE amp OPD vs FIFLD lark Cond 11 to FULL FIELD 7Sdeg 0 7 FIELD 69 1deg ON AXIS _ Odeg 0 05 0 025 0 0 025 0 05 FOCUS SHIFT UAF Phys452 Wide Angle lens Mark fanne CD ADA ANIA c lar 07 SPOT DIAGRAM ANALYSIS 01 18 AM 0 2 20 pies T 16 d 5 ES 0 126 4 12 F 5 F 55 S YN 0 08 H 18 amp 0 04 44 l 0 0 0 2 0 4 0 6 0 8 1 0 Fractional Object Height FBY Monochromatic wv1 0 5876um UAF Phys452 Wide Angle lens SPOT SIZE amp OPD vs FIELD forks pond This is a definite improvement Note the change of scale in the spot diagrams This can also be seen for the ray crossing diagrams which looked like this before optimization 12 Field 75 deg 1 mm ASTIGVATISM LONGITUDINAL CHROMATIC Sx T m SPHERICAL ABER mm FOCAL SHIFT mm E 0 7 AN j um NN 4 m Field 69 1 deg l 195 1 mm 2 2 3 5 ED SS H 7 9 HR AXIS Ec 1 mm 100 LATERAL
8. COLOR mm 0 2 AAA i ne E o UNITS mj FIELDS Jodeg UAF Phys452 Wide Angle lens Maris Conde IMAGE NA 0 268 EFL 9 31mm D Y 08 Mar 07 WAVELGTH 0 588 4 0 486 9 0 656 pm RAY TRACE ANALYSIS 01 21 AM But after optimization became Field 75 deg 1 mm ASTIGMATISM LONGITUDINAL CHROMATIC Sx T mm SPHERICAL ABER mm FOCAL SHIFT mm tT x o T5 V E X Field 69 1 deg 1 mm SON E p DISTORTION ES AXIS Sg 1 mm 100 LATERAL COLOR mm A 0 2 p 0 2 Ps ede O oe UAF Phys452 Wide Angle lens oe 3 to 9 35mm TTC 8 Mar WAVELGTH 0 588 4 0 486 9 0 656 um RAY TRACE ANALYSIS 01 23 AM The optimization modified the lens to look like this 13 UAF Phys452 Wide Angle lens UNITS MM FOCAL LENGTH 9 546 NA 0 2675 DES Mark Conde Note that there were several error messages that had to dismiss while the optimization was in progress suspect these may be related to the second element almost crashing into the first in the final version of this lens To complete this section would like you to try reloading the original lens but optimize it under a few different scenarios e Try a smaller maximum field angle 50 Does OSLO choose a different lens design if you only need a narrower field e Try changing the glasses
9. The Petzval radius You should also experiment with the Evaluate gt Aberration coefficients functions of the software These give text tables of aberration coefficients of the system We will not use these coefficients directly Nevertheless we will later on pass some of them into an error function that will be used to evaluate and to optimize our lens design Qualitative aberration evaluation Next you should examine qualitatively the imaging performance of this lens It is far from perfect Begin with the spot diagram analysis that we used last week In the graphics window click the setup window toolbar button E and select spot diagram Make sure to set the solve condition for the screen thickness to auto focus for minimum polychromatic RMS spot size and refresh the spot diagram analysis to ensure the display reflects the auto focused screen position Indeed believe you need to redo the auto focus operation after almost all changes that you make OSLO does not seem to automatically track the changing focus In some cases it is worth focusing paraxially first to give the auto focuser a sensible start point The scales etc that OSLO chooses for spot diagrams created using menu buttons may not be ideal in all cases You can get a more customized set of spot diagrams by typing the following command into the command input line at the top of the surface data spreadsheet window rpt spd lt nrays gt lt defocus gt lt npos gt
10. University of Alaska Fairbanks Phys 462 Lab Session 6 Lens analysis and optimization UNITS MM ES Mark Conde D UAF Phys452 Wide Angle lens ENGTH 9 312 NA 0 2685 FOCAL L cy tH ES NW mass uat Ki ZANI SA N ASS IZ VLDE xd y ad y P General Information Location Room 113 NSCI Session Times Thursday March 06 2014 Report due Thursday March 23 2014 Title Lens analysis and optimization Purpose e To analyze and characterize the aberrations present in potential designs for a wide angle lens and a telescope using computer ray tracing e To attempt to improve upon the initial designs provided Equipment e PC computer e OSLO optical ray tracing software Methods This is again a computer based virtual lab Unlike last week you are much more on your own this time We will be conducting this week s session in the PHYS175 Astronomy lab where every student can have his or her own computer to work on have designed a simple 4 element wide angle lens and a telescope Your task for today is twofold 1 Use OSLO to evaluate how good my designs are 2 Use OSLO to attempt to improve upon my designs The OSLO functions that you will need include Paraxial setup analysis paraxial ray analysis calculation of aberration coefficients Spot diagram analysis Ray crossing diagrams a
11. age Provide your name the experiment date and the title of the lab session 2 Tabulation of data and Analysis of Results For both the wide angle lens and the telescope you should include here A lens drawing of the original design A lens drawing of your best effort at an improvement on it Some captured graphics illustrating the performance of the original design along with corresponding graphics for the modified design showing improved performance 4 Additional Discussion For this lab your discussion should address the various questions posed in the instructions written above and especially Comment on any problems you observed with the original lenses What design difficulties did you encounter when trying to improve them manually How did the computer improve on my designs That is discuss how the graphics that you included in the previous section demonstrate improved performance Were you able to do even better than the examples gave in the notes by manually varying any of the other design parameters glasses properties lens thicknesses surface curvatures before starting the computer optimization Comment on the original and improved performance for the telescope at one degree half angle field would a view of the moon look very clear in this telescope 5 Original Notes Attach a photocopy of your original notes taken during the lab The purpose of this is to demonstrate that you were not only present in the la
12. b but also that you participated fully enough for you to show that the content of your report is based on your own measurements and your own understanding of what was actually done These notes are usually not neatly prepared but they do represent your only true record of what you did Your goal is to record enough information to convince me that you could in principle at least still adequately write up 20 what you did at some time in the distant future when your immediate memory has faded You may type your measurements directly into a computer file if you wish but these results must be accompanied with ample free text explanation of what each measurement actually is And you ll still need lots of diagrams 21
13. m RAY TRACE ANALYSIS 12 47 AM By reading your lecture notes and pages 99 100 and 107 112 of OSLO s Optics Reference manual you should be able to interpret these diagrams Copy the diagram to your report and write a few sentences describing what it shows Next try the lateral chromatic shift and Distortion plots using these toolbar buttons PH Make copies of the relevant plots and describe in your report what they show Finally go ahead and experiment with the Wavefront Transfer function Spread function and Energy distribution evaluation tools You need not include any of these results in your report but do want you to explore what they offer Exploration of the lens behavior Next we will explore how this lens behaves How feasible is it to improve on what have provided simply by trial and error Bear in mind here that we cannot determine what is an improvement without some specification of the intended application for the lens As stated earlier we are imagining this as an ultra wide angle lens for a large format camera Thus the properties that we desire include e The effective focal length should remain similar to what it is now i e around 9 mm if we are to map the same field of view onto the film e The film plane of our camera will be flat thus the lens focal plane should likewise be kept flat to match e Of course we want to minimize all aberrations that wo
14. nd analysis Distortion plotting Slider wheel parameter input Automated optimization We will be copying and pasting output from OSLO into word for use in your report strongly urge you to type a caption next to each graphic or table that you paste in This will allow you to write much of your lab report as you go along Note that we will be using the student version of OSLO here Anyone can download this for free from http www lambdares com The student version is however limited to only 10 surfaces Detailed procedure Getting started We will begin the session with an overview of our objective the tasks ahead of us and content that will be required in your report Each person should get setup on their own computer in the lab Start the OSLO program by clicking on the OSLO icon on the desktop A OSLO Dismiss any annoying dialogs about user tips or recently used files strongly recommend that you read the user manual pages that have attached to the lab handout preferably before we start the lab itself Lens overview Open the lens file Phys462 lab6 wide angle len that have placed onto Blackboard Use the lens drawing tools that we learned about last week 31 G E G to obtain an overview of the lens that we will be working with You be able to get something like this for a lens diagram UAF Phys452 Wide Angle lens UNITS MM FOCAL LENGTH 9 312 NA 0 2685 DES Mark Conde 10 1 AAA
15. of moderate complexity such as camera lenses and other systems having three to eight elements It is not sufficiently comprehensive to handle very large systems and is not efficient for handling singlets or doublets As noted above you should specify a spatial frequency for the GENII function to optimize at The relevant dialog box is shown below found that a value of 50 line pairs mm presume worked well for me Design frequency 1000000 Fifymax 0 900000 F2fymin 0900000 F2fymax 0800000 F2 0 800000 F3fymin 0800000 F3fymax 0700000 F3 1000000 F2 distol 1000000 F3 distol Cancel Help designed this lens to work over a very wide field of view at least 70 half angle This is horrendously wide by any measure my lens is definitely a fisheye that is pushing the limits of a 4 element design Nevertheless OSLO does quite well at field angles up to 75 or more have already specified in the lens file which parameters the optimizer should vary and this is a good start Now save a copy of your lens then 10 press the optimize button to let OSLO attempt to improve on you design When did this starting with UAF Phys452 Wide Angle lens UNITS MM FOCAL LENGTH 9 312 NA 0 2685 ES Mark Conde O 10 1 FULL FIELD 75deg a 0 7 FIELD 2 69 1deg a ON AXIS A Odeg m e e e 0 05 0 025 0 0 025 0 0
16. ossing plots became 17 Field 0 5 deg mm ASTIGMATISM LONGITUDINAL CHROMATIC S x T mm SPHERICAL ABER mm FOCAL SHIFT mm i 0 7 VA A A 0 6 Field 0 35 deg o5 2 mm 10 i o 2 2 E i 10 t St 3 i DISTORTION 153 E 5 E di AXIS 2mm LI 8 AR itum soil 6 UNITS mm FIELD O 5deg PHYS462 Lousy Telescope Conde IMAGE NA 0 108 EFL 835mm D v 08 Mar 07 WAVELGTH 0 588 2 0 486 5 0 656 pm RAY TRACE ANALYSIS 01 51 AM And the new spot diagram appearance was FULL FIELD O 5deg 0 7 FIELD O 35deg A 4 4 A ON AXIS PT Odeg A e d 0 1 0 05 0 0 05 0 1 FOCUS SHIFT SPOT SIZE amp FOCUS SHIFT UNITS mm PHYS4 6 Lousy Te l escope Conde NO ae SPOT DIAGRAM ANALYSIS iu 18 9 5 20 S dub 416 N a EU 0 3 412 2 S YO 0 2 48 m we o 1L ape 44 _ Sa 0 0 0 2 0 4 0 6 0 8 qe Fractional Object Height FBY Monochromatic wv1 0 5876um PHYS462 Lousy Telescope Sord SPOT SIZE amp OPD vs FIELD PY Clearly the new system performs much better What aberrations remain Try optimizing the system to work out to a field angle of 1 degree You will find you need to fix up vignetting at the eyepiece which will need larger and thicker lenses there 19 Content of Report 1 Title P
17. pens as you change the field angle of the illuminating rays There are no best answers to many of these questions in many cases gains in one area reduce performance in others But do want you to show by example graphics and by relevant captions that you ve experimented with varying some aspects of the lens and observed what a difficult task it is to improve the design Automated optimization Finally you should try OSLO s automatic optimization capability You will rapidly discover that this is by no means a hands off point and click operation At least for this lens OSLO will often produce bizarre and unphysical solutions from its optimization You need to hold its hand and ask it only to attempt small and simple tasks each time Once again backup your work very frequently during this phase As we did last week we must first setup and error function for OSLO to minimize This time we will select OSLO s pre built GENII error function as shown below Po UAF Phys452 Wide Angle lens Phys462 lab6 2007 v6 len OSLO EDU File Lens Evaluate Optimize Tolerance Source Tools Window Help EN 2c ES Cosas d Singlet Error Function Tables Cemented Doublet Operands Su Variables OSLO Spot Size Wavefront Slider Wheel Design Aberration Operands Ray Operands mm Su Field Point Set Advanced Optimization Draw On Group Notes
18. s452 Wide Angle lens Ef1 Ent beam radius 2 500000 Field angle 75 000000 Primary wavin RADIUS THICKNESS APERTURE RADIUS GLASS 0 000000 1 0000e 20 3 7321e 20 AIR 000000 1 000000 25 000000 K N BK7 888889 2 8 000000 W 25 000000 P AIR 7 230769 2 1 000000 10 000000 K N BK7 PJ 739979 12 000000 W 10 000000 EK air J 000000 v 587268 5 9 000000 A sF10 691590 y 867548 MW 9 000000 AIR J 341629 y 741719 5 15 000000 sr10 000000 W 000000 2 15 000000 Pj AIR J 0 000000 790890 2 60 000000 2 bm BOOOOOOOOO f mew 2 3 a Last mes In order to make the glass materials adjustable by sliders you need to define the glass to be a model rather than a fixed material from a catalog The graphic below illustrates this Surface Data een Setup Wavetengen variables Lens UAF Phys452 Wide Angle lens Ent beam radius 2 500000 Field angle Draw on Group Notes 2 Ef1 7 046078 75 000000 Primary wavin 0 587560 SRF RADIUS THICKNESS APERTURE RADIUS 083 0 000000 1 0000e 20 3 7321e 20 60 000000 22 1 000000 E 13 888889 2 3 726861 v 19 230769 22 1 000000 2 6 739979 15 979247 v 1 5440e 03 V 2 760896 5 16 177193 V 1 796709 v 22 238538 V 10 863605 s 56 084318 v 0 000000 J o 000000 11 640700 2 25 000000 Kj 25 000000 P 10 000000 K 10 000000 X 9 000000
19. uld blur the final image notably spherical aberration coma and astigmatism e We should assume our lens users would want to take color photos so we ll need to minimize both axial and especially lateral chromatic aberration e As mentioned in class we ll not worry too much about distortion It is impossible to map a really wide field onto a plane without some distortion anyway And of course these days we can easily digitize our images and re map them by computer to apply any distortion correction that we wish Our task here is simply to vary by trial and error the various curvatures thicknesses refractive indices and Abbe numbers that define the lens You could tackle this section simply by typing new values into the lens data entry spreadsheet cells However you would rapidly find that this becomes tedious A better alternative is to setup a slider control for each parameter using the 2 toolbar button We won t be wanting to activate a callback to any optimization functions here but it certainly would be good to activate the Spot diagram and All points image evaluation options This will provide real time updates of the spot diagrams as you vary the lens parameters You should also ensure you have an auto drawn lens diagram available as you adjust the lens parameters To do this just press the Draw on button in the main lens data entry spreadsheet e 3 S Y y gt E E m rd il Lens UAF Phy
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