Laboratory 5

Telescopes and Microscopes

Objective:

In this laboratory students will use Oslo to design, and components from the "Projects in Optics" kit and 2'' lens kit to build a simple Keplerian telescope, a terrestrial telescope with an erecting lens, a Galilean telescope, and a compound microscope.

Equipment:

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Lens Kit

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Meter Stick, Ruler

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Oslo LT

Procedure:

Keplerian Telescope

Select lenses from the "Projects in Optics" kit and 2'' lens kit to build a Keplerian telescope with magnifying power MP ~ 5X - 10X.  Look up the surface data for these BK7 precision lenses.  Use a 2'' lens for the objective and a 1'' lens for the eyepiece.  

A Keplerian telescope

 

Images of targets with a camera replacing the eye

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Build your telescope on the optical rail.  You can easily slide the components along the rail without destroying the alignment.

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Evaluate the performance of your telescope by viewing a distant object.

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Model your telescope with Oslo.  Enter the surface data as described in the write-up for Lab 3.
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The aperture stop of your telescope is the objective lens.  It is your goal to make an incident (approximately) parallel beam from a distant source point, which makes an angle θ with respect to the optical axis, emerges as a parallel beam which makes a larger angle θ' with respect to the axis.

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Use the slider wheel option of Oslo to find the distance between the two lenses that yields an emerging parallel beam for an incident beam with a field angle of 1 degree.  The slider wheel option allows you to pick a particular parameter and change its value while monitoring the effect in a graphics window.

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Choose the slider wheel icon from the main-screen toolbar.  It is the second icon from the right.

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Change the number of slides to 1.

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If you want to change the distance between the objective and eyepiece, change the "surf" parameter to 3, since the distance is the thickness associated with this object surface.

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Double-click the "item" cell and a list of parameters will appear.  Choose thickness and click the checkmark.

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A graphics window with a slider tool will appear on the screen. 

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Vary the thickness until the emerging beam is parallel.  Then click "evaluate", "paraxial setup" on the main menu and note the positions and radii of the entrance and exit pupils.  The ratio of the diameter of the entrance pupil to the exit pupil is equal to MP.

Back of the envelope calculations:

Keplerian telescope, fe << fo, object at infinity:

aperture stop: objective
entrance pupil: objective
exit pupil: (1/(fo + fe) + 1/xi = 1/fe,  xi = fe(fo + fe)/fo
diameter of exit pupil: (fe/fo) * diameter of objective
field stop: eyepiece:
entrance window: (1/(fo + fe) + 1/xi = 1/fo,  xi = fo(fo + fe)/fe
diameter of entrance window: (fo/fe) * diameter of eyepiece
field of view: tanθ = diameter of eyepiece/(fo + fe)

Example: 2'' objective, fo = 300 mm,  1'' eypiece, fe = 50 mm,  MP = 6X
exit pupil: xi = 58.33 mm
diameter of exit pupil:  8.5 mm
field of view: tanθ = 0.0726,  θ = 4.15o, full cone angle.

Terrestrial Telescope

Design and build a terrestrial telescope with magnifying power MP ~ 5X - 10X.

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Select a bi-convex erecting lens to be mounted between the objective and eyepiece.

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Evaluate the performance of your telescope by viewing a distant object.

Example: 2'' objective, fo = 300 mm,  1'' eyepiece, fe = 50 mm,  2'' erecting lens, fi = 50 mm
aperture stop: objective
entrance pupil: objective
exit pupil: xi = 108.33 mm
diameter of exit pupil:  8.5 mm
field stop: eyepiece
field of view: tanθ = 0.039,  θ = 2.24o.

Galilean Telescope

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Design and build a Galilean telescope with magnifying power MP ~ 5X - 10X.

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Evaluate the performance of your telescope by viewing a distant object.

 

   

A Galilean telescope                                      An image with a camera replacing the eye

Back of the envelope calculations:

Galilean telescope, fe is negative, |fe| << fo, object at infinity:

aperture stop: objective
entrance pupil: objective
exit pupil: (1/(fo + fe) + 1/xi = 1/fe,  xi = fe(fo + fe)/fo
diameter of exit pupil: (|fe|/fo) * diameter of objective
field stop: eyepiece:
entrance window: (1/(fo + fe) + 1/xi = 1/fo,  xi = fo(fo + fe)/fe
diameter of entrance window: (fo/|fe|) * diameter of eyepiece
field of view: tanθ = diameter of eyepiece/(fo + fe)

Example: 2'' objective, fo = 300 mm,  1'' eyepiece, fe = -50 mm,  MP = 6X
exit pupil: xi = -41.66 mm
diameter of exit pupil:  8.5 mm
field of view: tanθ =0.1,  θ =5.8o.

Compound Microscope

Design a simple compound microscope with  a tube length g of 160 mm and a magnifying power MP ~20.  160 mm is the most common tube length for laboratory microscopes.  Use the 38 mm focal length 2'' converging lens as the objective and the 50 mm focal length 1'' diameter converging lens as the eyepiece.  Let the center to center distance between the lenses be ~25cm.  Place the target ~5 cm in front of the objective.

     

A compound microscope                               An image with a camera replacing the eye

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Build the microscope on the optical rail.

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Evaluate the performance of your microscope by examining a tiny object of your choice.

Laboratory Report:

Open Microsoft Word and prepare a report using the template shown below.

Name:
E-mail address:

Laboratory 5 Report

bulletIn a few words, describe the experiment. (What?)
bulletIn a few words, state the objective of the experiment. (Why?)
bulletComment on the procedure.  Did you encounter difficulties or surprises? (How?)
bulletPresent your results and comment on your results.