Using The Setting Circles - Celestron FIRSTSCOPE 80 EQ Instruction Manual

c.
Using the Setting Circles
Setting Circles are dials (or gauges) for right ascension and declination that allow you to locate
celestial objects easily from their coordinates as listed in a star chart or atlas.
1. The declination setting circle is scaled in degrees and the right ascension setting circle is
incremented in minutes. The circles will get you close to your target but not directly on it. Also,
the accuracy of your polar alignment will affect how accurate your setting circles read.
2. The declination setting circle is factory set and should not need any adjustment if it reads
accurately as noted in 4.B (7).
3. The right ascension setting circle (#25) must be aligned. Choose a bright and easy to find star in a
star chart and note the coordinates (right ascension and declination). Find the star and center it in
the finderscope and then in the telescope. Now, rotate the right ascension circle to match the
coordinates of the star with the indicator mark.
4. The right ascension setting circle does not move as the telescope moves in right ascension and
thus it must by aligned each time you want to use it to find a new object. However, you do not
need to use a bright star each time but you can use the object you are currently observing.
5. Now, using a star chart or atlas you can find numerous objects. First move the telescope in
declination to the correct declination coordinate. Then move the telescope in right ascension until
the indicator points to the correct coordinate.
6. After moving the telescope to the correct celestial coordinates, look through the finderscope to see
if you have located the object and center the object. Then, look through the telescope (with a low
power eyepiece) and the object should be there.
On fainter objects, they may not be visible in the finderscope and thus you should gradually sweep the
telescope around (with the right ascension and declination cables) until the object is visible.
5. MAGNIFICATION (POWER)
The magnification (or power) of a telescope is variable depending upon the focal length of the
eyepiece being used along with the focal length of the telescope.
A. Your telescope has a focal length of910mm and comes with a 25mm 1-1/4" eyepiece.
To calculate the magnification we use the following formula:
. . -
FL(telescope)
Magnification =-
FL(eyepiece)
where FL(telescope) is the focal length of the telescope and FL(eyepiece) is the focal length of the
eyepiece. So, if you use the 25mm eyepiece your magnification is 910/25 = 36x.