Geometric Optics

 Telescopes and Fresnel Lenses

 Seat Experiment

 During this activity we will concentrate on Keplerian and Galilean telescopes; telescopes made with two lenses instead of a combination of lenses and mirrors. Using converging and diverging lenses we will construct two telescopes and examine their similarities and differences. When discussing these telescopes, the lens close to your eye can be referred to as the eyepiece and the further lens is the objective.

 Hold a diverging lens close to your eye and a converging lens just beyond the first. You should now be looking through both lenses. Close your other eye and look towards an object in the distance. Slowly move the converging lens away from you until you see a sharp focused image. Congratulations, you have created a Galilean telescope. Q1: How does what you see through your telescope differ from the actual object? Draw a ray diagram.

 Now, hold a converging lens close to your eye and a second converging lens just beyond the first. You should now be looking through both lenses. Close your other eye and look towards an object in the distance. Slowly move the second converging lens away from you until you see a sharp focused image. Congratulations, you have created a Keplerian telescope. Q2: How does what you see through your telescope differ from the actual object? Draw a ray diagram

 For the next two questions make sure the distance between the object and the lens or telescope remains constant. Q3: Look through a converging lens. Now look through your Keplerian Telescope. How are the two images different? Why are they different? Use a ray diagram in your explanation if needed. Q4: Look through a diverging lens. Now look through your Galilean Telescope. How are the two images different? Why are they different? Use a ray diagram in your explanation if needed.

 References

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