Your Home Observatory Practice Problems

By — McGraw-Hill Professional
Updated on Sep 19, 2011

Review the following concepts if needed:

Your Home Observatory Practice Problems

Refer to the text if necessary. A good score is 8 correct. Answers are in the back of the book.

1. A telescope has an f -ratio of f /5. The magnification is 100×. What is the focal length?

(a) 500 mm

(b) 20 cm

(c) 100 mm

(d) It cannot be determined from this information.


2. A telescope has an objective focal length of 1,000 mm, and the eyepiece has a focal length of 25 mm. A 2× Barlow lens is used. What is the magnification?

(a) 20×

(b) 40×

(c) 80×

(d) It cannot be determined from this information.


3. Some telescopes have a tendency to produce blurring near the outer edge of the field of view, even when things are in perfect focus at the center. This is called

(a) coma.

(b) dispersion.

(c) chromatic aberration.

(d) depth of field.


4. The optimal position of a solar filter in an SCT is

(a) in front of the objective.

(b) between the objective and the secondary mirror.

(c) between secondary mirror and the eyepiece.

(d) between the eyepiece and the observer’s eye.


5. You see a pair of binoculars in a surplus store. You see “7 × 70” stamped on them. The diameter of the objective lenses is

(a) 10 cm.

(b) 70 cm.

(c) 0.1 m.

(d) 70 mm.


6. Suppose that an SCT has a magnification of 200× with a particular eyepiece. A focal reducer/corrector that cuts the f -ratio by 37 percent is installed. What is the resulting magnification if the same eyepiece is used?

(a) 63×

(b) 74×

(c) 126×

(d) 200×


7. The bearings of a properly adjusted fork mount/wedge move the telescope along coordinates of

(a) compass direction and elevation.

(b) celestial latitude and celestial longitude.

(c) azimuth and altitude.

(d) right ascension and elevation.


8. The light-gathering area of a refracting telescope is

(a) proportional to the objective diameter.

(b) proportional to the square of the objective diameter.

(c) proportional to the f -ratio.

(d) proportional to the magnification.


9. A filter that allows all light to pass through, with the exception of light at a single wavelength, is called

(a) broadband.

(b) line-type.

(c) planetary.

(d) lunar.


10. A prism that turns the path of the light rays entirely by means of total internal reflection is called

(a) a dispersive prism.

(b) a reflective prism.

(c) a flint prism.

(d) a porro prism.



1. D

2. C

3. A

4. A

5. D

6. C

7. B

8. B

9. B

10. D

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