AY 105 Lab Experiment #3: Optical aberrationsPurposeIn this lab you will study the imaging performance of real lenses, that is, thoseused in the non-ideal case of real world optics. You and your lab partners will simulateoptical raytracing using a computer program on a PC in the lab, and compare thecalculated results to the performance of actual optical elements on the lab benches.In the first day’s lab you will study lenses (an achromatic doublet and a plano convexlens) while learning the basics of the ’Code V’ program. In the second day’s lab youwill study far off-axis images from a concave mirror.Pre-lab Work• Skim the lab but don’t worry to o much about understanding the software in-structions as these technical parts are better appreciated when you see them inoperation.• Skim the additional material on the CodeV ray tracing software so that you havean idea of what optical design is all about. This chapter from the software User’sGuide goes through the case of a digital camera lens, which is not our situation,but it’s helpful nonetheless.• Review basic concepts in optical abberation (i.e. deviation from the simple par-axial optical theory we have been using thus far) such as: spherical ab erra-tion, astigmatism, coma, field curvature, distortion, chromatic aberration, lateralcolor.BackgroundDiffraction, refraction, reflection, and scattering are all important processes thataffect photons from the time when they are incident on the first optic and as they pro-pogate through the system to the detector. Ray tracing is commonly used in opticaldesign to simulate the behavior of light waves as they travel through sometimes very so-phisticated instru ments. In general, raytracing programs take as input the parametersof lenses and other optical elements, then produce drawings such as “spot diagrams”to visualize what your perfect incident wave looks like at the end of the optical train,and analyze the image quality of an optical system.Code V (pronounced “code-five”) is an industry-standard optical design softwarepackage written by Optical Research Associates of Pasadena. Although it is a quitepowerful system, the command interface can be somewhat perplexing. A menu-basedmode (“screen mode”) is operated through the “Lens Data Manager” window and is1Ay 105 Spring 2011 Experiment 3 2designed to ease data entry. Advanced users may wish to learn the command linelanguage and type into the box at the bottom of the Command Window.Equipment ListPC w/ Code V (note that a license update is needed each year)QTH Lamp #63200Power Supply #6394Opal Glass DiffuserCondensing Lens (50mm diameter, 75mm focal length)25 micron (one group) or 30 micron (other group) Pinhole75 mm Diameter Photographic Telephoto LensMicroscope w/ x,y,z AdjustmentsAchromatic Doublet #31402Plano-Convex Lens #32974 (50 mm Diameter, 150 mm FL)Reference Flat3-point Spherometer (one group) or single-point (other group) SpherometerCenter Thickness Gauge (share between groups)Rotational Stage80 mm EFL f/2.8 triplet Lens (optional)Adjustable Mirror MountMirror 1 m RoC, 500 mm FLHeNe LaserLaser mount and positionerExperimentPart A: LensesPart A Configuration - Optical BenchYou will either find the optical table already configured with a collimated lightsource illuminating your test lenses, and a microscope to examine the resulting images(highly recommended for the motivated TA), or you will have to set this up using yournow-honed skills in optical alignment. Remember during to check the prop erties (e.g.location, size, brightness) of the light ray bundle as it proceeds through your opticaltrain to make sure the behavior is as you expect, notably b efore and after each opticalelement.The collimated light is provided by the QTH lamp, opal glass diffuser, and acondensing lens to concentrate the diffuse light onto a pinhole. One group’s pinhole isAy 105 Spring 2011 Experiment 3 325 µm diameter, while the other group’s is 30 µm diameter. Light emerging from thepinhole is diverging, but is then collimated by a photographic telephoto lens, producinga parallel beam roughly 75 mm in diameter in which you will locate your test lenses.The collimated beam travels the length of the optical rail, at the other end of whichis located a microscope that can make fine adjustments in each of the “x, y, and z”directions. Make sure there are lenses in the microscope (10x will do). The test lensholder will be mounted on top of the rotational stage on the rail carrier, between thetelephoto lens and the microscope. You will test both an achromatic doublet lens anda plano-convex lens.Sketch the setup thus far in your lab notebook, recording the diameter of yourpinhole, the EFL (effective focal length) of your telephoto lens, and the magnification ofyour microscope. As always, label the relevant dimensions. What angle in arcsecondsis subtended by the pinhole diameter in the focal plane of the telephoto lens? Thereare a number of different telephoto lenses around; which properties of these lenses willproduce the smallest pinhole image and is smaller always better?Before taking actual measurements with the lenses you will first construct a modelfor their behavior.Part A Configuration - PC ModelNow move to the PC computer. Start Code V by double-clicking its icon on theWindows Desktop. Eventually the Code V session will start and several windows willappear. In Code V, optical elements are entered one-by-one in the sequence of surfacesthey present to light rays entering the system. These surfaces are denoted as “S0”(object plane), “S1” (first optical surface), “S2” (second optical surface), etc.The precise commands needed to enter the lenses used in the lab are given below.Try to pay attention to the reasoning behind the commands, rather than just readingand following directions. You may wish to switch among the partners in navigatingthe Code V command execution, or have specialists.Part A Measurements - PC Model for Achromatic DoubletFor the achromatic doublet lens there are two surfaces for the positive (crownglass) element and two for the negative (flint glass) element.First, name your lens file by going to the File menu and choosing “Save As.”The software will add “.len” to the end of the filename you specify and save the lensdefinition in C:\CVUSER. You can begin by entering the parameters for the achromaticdoublet lens. Enter a title for your lens by clicking on the Lens menu, choosing