Class Note for OPTI 510L at UA
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Date Created: 02/06/15
Experiment 62 The Nodal Slide The nodal slide is an instrument used for locating and measuring the cardinal points of a lens or a system of lenses It allows F Fa H H N and N to be located with respect to the vertices of the lens or lens system This is important as the vertices are the only physical landmarks of a lens accessible for alignment and measurement The cardinal points themselves are usually points in space or in the interior of a lens that are dif cult or impossible to align to Refer back to Figure 66 which shows a lens and the nomenclature used for this lab if the indices of object and image space are identical the nodal points and principal points of a lens coincide H and N are coincident and H and N are coincident Assume that a lens or system of lenses is illuminated with a collimated beam of light mmmamdmsmmmmmmmm image appears stationary Even thouah the lens rotates the imaae does not At this point N and H are known to be located over the axis of rotation Measurement of the distance between the rear vertex and the image gives the back focal distance BFD By next positioning the rear vertex of the lens over the axis of rotation 6 is measured At this point the positions of H N and F are known with respect to the rear vertex The lens is turned around endforend and the process repeated to nd the other three cardinal points A drawing of the nodal slide used in this lab appears in Figure 67 A rotation stage slides along the optical rail on a carrier that may be locked down at any position The rotation may also be fixed with a locking screw located on the side of the stage Note that the center of rotation is coincident with the marker line on the carrier On top of the rotation stage is fixed a precision slide stage with a lens holder on the movable part of the stage The position of the lens on the slide is read with a vernier scale having a resolution of 120 mm or 50 microns This arrangement of stages allows any part of the lens to be positioned over the center of rotation of the rotary base It is this feature of the nodal slide that allows the cardinal points of a lens to be measured in particular the nodal points themselves N and N2 Note that the vernier scale is not referenced to any particular point The readings taken will be referenced to the vertices and cardinal points of the lens under test The detailed use of the nodal slide is now outlined Follow the steps given to determine the cardinal points of the lenses provided CoryIdiomsMHdmw Copyrlgh O 1995 Michel Jule No ger Figure 65 Cardinal points of a thick lens 205 210 LENS SLIDE STAGE VERNIER SCALE J 39 i 4 4c amusuw norm snot 39 cums Fugue 67 Nodal slidemechanical layout Cowonmwmnm 211 WCPQSCCSE O LOCATES AXIS 0F ROTATIC 2 THE NOOAL SLIDE Fugue 8amp Use of the nodal slide cm diclmmadumnm 212 1 FORM AN IMAGE WITH THE LENS Mount a lens in the holder on top of the nodal slide Position the light source so the diffuse pinhole aperture is on the optical axis of the lens Lock down the position of the source Position the microscope at the opposite end of the rail and lock it down on one of the rail markings Form an image of the source in the microscope by moving the entire nodal slide along the optical rail Adjust the height of the microsopce until the image is in the center of the crosshairs Lock down the position of the nodal slide along the rail Record the location of the microscope 2 POSITION H AND N OVER THE AXIS OF ROTATION While looking through the microscope at the focused image rotate the nodal slide 1 020 degrees in either direction Notice that at this point the image will also rotate Move the slide stage in one direction refocus the image by moving the entire nodal slide and again rotate the nodal slide tf the image rotation appears less repeat thii process until the image appears stationary with rotation of the nodal slide If the image rotation appeared greater after the first attempt move the slide in the other direction and repeat the process until the image appears stationary At this point H and NI are over the axis of rotation of the nodal slide Figure 68 a shows the situation Record the reading of the vernier scale on the nodal slide 3 MEASURE ME BACK FOCAL LENGTH BFL Move the microscope fonNard until it is focused on the rear vertex of the lens closest to the image A small amount of dust on the lens surface makes this easy to do Record the location of the microscope WW I I E m H 4 POSI39ITONTHELENSVERTEXOVERTHEA SOFHOTATION Rotate the nodal slide Observe the image of the lens surface Move the slide stage a small distance refocus the microscope on the vertex and rotate the nodal slide Observe the image of the lens surface If the image rotates continue this process until the image appears stationary At this point the lens vertex is over the axis of rotation of the nodal slide Figure 68 c shows the situation Record the reading of the vernier scale on the nodal slide WWW 6 42 CWOlmM ndJauw 213 ROTATE THE NODAL SLIDE 18039 TO MEASURE THE OTHER SIDE OF THE LENS DO NOT ROTATE JUST THE LENS OR ITS HOLDER 5 POSTUON H AND N OVER THE AXIS OF HOTA HON Repeat the procedure in step 2 above to position H and N over the axis of rotation of the nodal slide Record the reading of the vernier scale on the nodal slide Calculate t1H as the absolute value of the difference in readinas in steps 2 and 39 HrHa 35 Record the location of the microscope 6 MEASU RE THE FRONT FOCAL LENGTH FFL Move the microscope until it is focused on the back surface of the lens actually the front vertex now that the lens has been rotated 180 Record the location of the microscope Calculate the front focal length FFL as the difference in locations of the microscope in steps 5 and 6 7 POSI39I39ION lELENSVEHTEXOVERTHEAXISOFROTA39I39ION Repeat the procedure in step 4 above to position the lens vertex over the axis of rotation of the nodal slide Record the reading of the vernier scale on the nodal slide W asthed39 ren inre in inst 61 8 In addition you also have enough data to calculate the thickness of the lens Calculate g the IE thickness as the absolute difference in readinas of the nodal slide vernier scale in gang 4 and Z t I 47 l CALCULATEANDREPOHT IELOCANONOFTHECARDINALPOINTSIN RELA39ITONTOTHEVERTICESOFTHELENS CWOIMWJlNo w
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