Ay 105 Lab Experiment #3: Geometric opticsIn this lab, you will study the optical properties of telescopes, eyepieces, and fieldlenses on the optical bench. In the first labs, you started with a clear optical table andset up all of the optics yourself; in this week’s lab, there will be some equipment setup on each bench. You’ll spend the first day at one setup (Part I or II), then switchplaces for the second day.Part I : Telescope imagingThe preliminary setup here features a 50 mm diameter, 260 mm focal lengthachromatic doublet collimator sending light from a test target into a 6-inch apertureMaksutov-Cassegrain telescope attached (somewhat precariously) to the optical table.The test target is illuminated by the QTH lamp from lab #1, but with a white opalglass diffuser between the lamp and the target for more even illumination. In additionto this write-up, there is also a handout of describing the pattern element line spacingsfor the USAF resolution test target. The telescope is equipped with a micrometereyepiece that contains a moving crosshair to measure the size of image features in thetelescope focal plane. Turn on the QTH lamp and record the measurements below inyour lab notebook.Measurements. Once you have learned how to read the test target patterns,use the micrometer eyepiece to measure the sizes of an element (one “line pair”) ineach group that is visible. You know from the “Line Pairs Per Millimeter” chart theactual sizes of each feature measured in the focal plane of the 260 mm lens, so fromyour measurements you can determine the effective focal length (EFL) for the 6-inchtelescope. Note that underneath the telescope at the eyepiece end is a small knob to beused for focus; make all of your micrometer measurements at a single telescope focussetting.Remove the eyepiece and eyepiece holder—the first just pulls out, while the holderis threaded into the telescope tube. Likewise remove the threaded cap in the center ofthe eyepiece end of the telescope. With these parts removed, describe in your notebookthe function of the two knobs at the back end of the telescope. Is the lens carried intoposition below the eyepiece a positive or negative lens? What will be the effect of thislens on the effective focal length of the telescope? Return the knobs to their originalpositions, and replace the parts you have removed. Move the knob that controls themotion of the lens inside the tube, and observe the result by looking into the eyepiece.Move the knob that controls the motion of the lens, and observe the result by lookinginto the eyepiece (turning the focus knob for sharpest focus). Does the result confirmyour expectation? Using the micrometer eyepiece again, re-measure at least one linepair spacing on the target to re-determine the effective focal length of the telescopeplus lens.1Ay 105 Spring 2008 Experiment 3 2Replace the micrometer eyepiece with the 40 mm, 15 mm, and 10.8 mm effectivefocal length eyepieces and record the target appearance for each. What is the outermostgroup you can see, what is the smallest element you can resolve with your eye, etc.Note that you may need to refocus the telescope for different eyepieces.Turn off the QTH lamp and put a white screen in front of the entrance to thetelescope; room light should illuminate the side of the screen facing the telescope. Witha second opal glass or ground glass diffuser, locate the exit pupil formed by each of the40 mm, 15 mm, and 10.8 mm eyepieces and measure the diameter of this exit pupil asaccurately as you can.Analysis. For each of your USAF test target measurements, calculate the anglesubtended by a line pair in the focal plane of the 260 mm lens and use this angletogether with your micrometer measurement to determine the EFL of the telescope.Use your error estimates to compute a weighted mean average for the telescope EFL.When the full 6-inch aperture of the telescope is used, what is the effective f/ratio ofthe telescope? What happens to the EFL and f/ratio when the small lens is insertedinto the beam beneath the eyepiece holder?Calculate the angular magnifications achieved with the 40 mm, 15 mm, and10.8 mm eyepieces. Dividing the 6-inch aperture by the magnification, predict the exitpupil diameter and compare the values you measured. What angular magnificationsand pupil diameters would you have found if the additional lens were used?Part II : Reimaging Systems and PupilsThis lab was originally designed to be performed with the use of two HeNe lasers,spatial filters, and 50 mm diameter laser collimators on the optical table. However, ifyou tried to make a large diameter colimated laser beam in Lab 1, you can recall thatthe equipment is very fragile and the slightest bump can ruin the alignment. Therefore,for the sake of efficiency, this lab can be done using colimated light of QTH lamps, asin Lab 1. You can try to set up a collimated broad laser beam, if you have unusualmechanical aptitude, plenty of time, and a lot of patience.You will notice that one beam is aligned with the long optical rail and will thisbe “on-axis” for any optics on the right side of the rail. The other collimated beam isat the same height above the table but is aligned at an “off-axis” angle with respect tothe long rail. You will use these two beams to simulate on-axis and off-axis ray bundlesto study focal planes, field lenses, and pupils.For tracking the beams more esily, we can also place different filters in front ofthe lamps (for example, a “green” filter for the “on-axis” beam and a“red” filter forthe “off-axis” one).Measurements. Begin by observing the collimated beams as they intersectAy 105 Spring 2008 Experiment 3 3and move apart. Estimate the rail scale reading that corresponds to the point ofintersection. Install the Nikon lens and carrier so that the two beams intersect in themiddle of the lens body. In your lab notebook, record the focal length of the lens(written around the front of the lens), and set the f/stop ring of the lens to a focalratio of f/5.6. You should feel the lens click into this stop position; you may need torotate part of the lens if it is mounted by the f/stop ring. Set the lens focus to ∞.Locate the focal plane of the lens and measure the separation between the “on-axis” and “off-axis” image by using the ruler as a screen. Measure the reading on therail scale corresponding to the focal plane.Turn your attention next to the patterns on the wall. Use the ruler to