CELESTIAL OBSERVING TIPS
This section covers visual observing hints for both solar system and deep-sky objects as well as general observing
conditions which will affect your ability to observe
MAGNIFICATION
You can change the magnification of your telescope by simply changing eyepieces Both telescopes and eyepieces
have focal lengths that are measured in millimeters To calculate the magnification of a given telescope and eyepiece
combination, take the focal length of the telescope and divide it by the focal length of the eyepiece The resulting number
is the magnification factor
For example, the AstroMaster LT 70AZ has a focal length of 700 mm Using the 20 mm eyepiece:
_________________________
Magnification =
FIELD OF VIEW
Determining the field of view is important if you want to get an idea of the angular size of the object you are observing To
calculate the actual field of view, divide the apparent field of the eyepiece (supplied by the eyepiece manufacturer) by the
magnification it gives you in the scope you are using
Using the example in the previous section, we can determine the field of view using the same telescope and 20 mm
eyepiece The 20 mm eyepiece has an apparent field of view of 40°
Actual Field Of View =
The 20 mm eyepiece has an apparent field of view of 40° Divide the 40° by the magnification, which is 35 power
This yields an actual field of view of 1 3 degrees arc
12
I
ENGLISH
Focal length of Telescope
Focal length of Eyepiece
Apparent Field of View of Eyepiece
________________________________
Magnification
700 mm
____________ = 35x
=
20 mm
40°
______ = 1 3 degrees of arc
=
35