AY 105 Lab Experiment #5: Optical aberrationsIn this lab you will perform optical raytracing using the computer program’Code V’ on a PC in the lab, and compare the calculated results to the performanceof actual lenses on the optical bench. In the first day’s lab you will study lenses (anachromatic doublet and a plano convex lens) while learning the basics of the program,then in the second day’s lab you will study far off-axis images from a concave mirror.LensesAt the beginning of the lab you will find the optical table already configured with acollimated light source to illuminate your test lenses and a microscope to examine theresulting images. The collimated light is provided by the QTH lamp, opal glass diffuser,and a condensing lens to concentrate the diffuse light onto,a pinhole. One group’spinhole is 25 µm diameter, while the other group’s is 30 µm diameter. Light emergingfrom the pinhole is then collimated by a photographic telephoto lens, producing aparallel 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 a microscope with x, y, and z fine adjustments. Make sure there are lenses inthe microscope (10x will do). The test lens holder will be mounted on top of therotational stage on the rail carrier. Sketch the setup in your lab notebook, recordingthe diameter of your pinhole, the EFL (effective focal length) of your telephoto lens,and the magnification of your microscope. Ask the instructor to explain the x, y, zmotions of the microscope and anything else about the initial setup which is unclear atthe start. What angle in arcseconds is subtended by the pinhole diameter in the focalplane of the telephoto lens?The Code V optical raytracing program runs on a PC.Start Code V by double-clicking its icon on the computer next to the storagecabinets. Eventually the Code V session will start and several windows will appear.First name your lens file by going to the File menu and choosing “Save As.” The soft-ware will add “.len” to the end of the filename you specify and save the lens definitionin C:\CVUSER We’ll begin by entering the parameters for the achromatic doublet lens.Enter a title for your lens by clicking on the Lens menu, choosing “System Data,”then System Settings and the option to set a title. Something like “Ay 105 achromaticdoublet” would b e a good choice.Go to “Lens → System Data” and the wavelength section to indicate that youwant to enterthree wavelengths. Specify a red, green, and blue wavelength in nanome-ters (e.g. 750, 550, 400). Other fields in this dialog box can stay at their default1Ay 105 Spring 2008 Experiment 5 2values.Click on the input window at the center of the screen, where you will already seethe object and image surfaces entered at infinity. Right click on the block that says“Image” and select insert. Insert two surfaces. The input window will then includelines for Stop and 2-3. Stop represents the aperture stop. For our lens, the stop issurface 1, so this is OK. You will enter the surface properties for the lens surfaces onthese lines.Specify the lens as follows.Surface Name Y Radius Thickness Glass Refract Mode X/Y Semi-ApertureStop 203.94 11.94 BK7_SCHOTT REFR 31.752 −156.41 8.86 SF2_SCHOTT REFR 31.753 −569.57 343.67 REFR 31.75The X and Y semi-aperture may appear gray in the screen, and not allow you toenter values. If this is the case, right-click on the surface number column, and choose“Surface Properties.” Enter the Y semi-aperture, and the X semi-aperture shouldadjust accordingly since you have specified a circularly symmetric lense. The “RefractMode” column specifies whether the surface is reflective or refractive. BK7 and SF2are types of glass, and Schott is the manufacturer. Ignore any error messages aboutthe glass no longer being available.Specify that we want to trace f/5.6 rays through the system by going to the “Lens→ System Data → Pupil.” Specifying a F/N value of 5.6. Save your lens definition.You can see a lot of data about the lens you have entered by going to “Display→ List lens data → All lens data.” You can also display a picture and a 3D model ofyour lens from the View menu or the various buttons at the top of the screen.We would like to evaluate chromatic aberration of this doublet. We’ll do that byproducing a spot diagram in front of, at, and b ehind the nominal focus. Go to “Lens→ System Data → Through focus” to define the focus positions we want to look at.We’ll look at three positions, starting position -1.5, increment 1.5 (so we the nominalfocus, plus 1.5 mm in front and b ehind).Having done that, go to “Analysis → Geometrical → Spot diagram.” The threespot diagrams will appear in their own window. (You may have to wait a bit).Print the spot diagram using “File → Print.” Make sure the spot diagram windowis in front. You can print to the lab printer – it’s called HP Laserjet 1100. If you preferto print a pretty colored plot, you can always ftp your files to another computer andprint elsewhere.Ay 105 Spring 2008 Experiment 5 3Which focus setting is best for red? for green? for blue? What does this tell youabout the achromatic doublet?Now, let’s make a field map showing the RMS spot size as a function of x and yfield angle. That is, we’ll see how the image of a point grows as we move off-axis. Go to“Analysis → Diagnostics → Field Map.” On the first panel page, open the drop-downmenu for type of display and choose “RMS Spot Diameter.” On the panel including“Field Description,” we want a range of field angles, so switch the pull-down menu to“Field Angle” and specify the X and Y field angles as having a minimum of -10 degreesand a maximum of 10 degrees. Then hit okay and wait until the diagram appears.Print it, if you’d like, and note your observations.You can perform other analyses by exploring menus. Remember to hit the okayafter setting the parameters, and look for plots in the plot window and textual resultsin the command window.If you want to add off-axis rays to spot diagrams and raytraces, you can addthem from the “Lens → System Data → Fields/Vignetting” menu by specifying moreX angles. I s the focal surface of the achromat a plane?Next you must apply the Code V commands you’ve learned from the Cookbo ok inorder to perform a raytrace analysis of the 50 mm diameter 150 mm EFL