Exercise

1. What are some of the differences between refracting and reflecting telescopes? (Drawing a diagram may be helpful.)

2. Is the Galileoscope a refracting or reflecting telescope? What type of celestial objects would you be likely to see using the Galileoscope? What kinds of objects would not be ideal for viewing with it?

3. What is an example of a reflecting telescope?

Take the telescope apart by removing the dew shield, twisting the locking ring, and lifting the halves of the body apart, as shown in the image at the top of the page. You should examine the objective lens. Be careful to only pick it up by the edges as to not smudge the lens. When you put it back together, the thin part of the lens should be facing out, i.e., toward the object you are viewing.

4. Why does the objective lens of the Galileoscope consist of two separate lenses fused together? You may need to research this answer.

You will now find the focal length of the objective lens. Read the background section on main page of this lab to guide yourself. You will need the objective lens and a meter stick to determine the focal length. 

5. Find and explain your method for determining the focal length of the objective lens.

Using the Eyepieces

Reassemble the Galileoscope. Be sure to put the end of the focusing tube interior to the first notch in the telescope tube. Otherwise, you will not be able to focus the telescope correctly.

You will now compare the view using three different eyepieces. The first is the Galilean eyepiece. You will need the small eyepiece and the ring cap as shown in the image below. The smaller side of the lens is inserted into the telescope.

6. Describe the view using the Galilean eyepiece. You should think about the magnification and the field of view. How do you think this would have affected Galileo’s observations?

You will now use the modern lens, which is the larger of the two eyepieces. It does not require any attachments.

7. Describe the view using the modern lens and compare the magnification and field of view to the Galilean eyepiece. Do you notice anything else that is different with the modern lens?

Now, you will assemble the Barlow lens. The Barlow lens requires the modern eyepiece, the Barlow tube, and the Galilaen eyepiece without the ring cap. The small eyepiece goes into the small end of the Barlow tube, the modern eyepiece goes into the larger side, and then the whole lens goes into the telescope with the small eyepiece in first.

8. Compare the view using the Barlow lens to that of the other two lenses. Explain the differences in field of view size, magnification, and any other parameter you may have noticed.

Magnification and Focal Lengths of the Eyepieces

9. The telescope with the Galilean eyepiece has a magnification of 17. Based on your observations, what is the magnification of the telescope with the modern eyepiece? What about the Barlow eyepiece?

10. Using the observed magnifications, calculate the focal length of the Galilean, modern, and Barlow eyepieces.

11. Your TA will now provide you with the real magnifications. Compare your observed magnifications with the real magnifications. How accurate were you?