Calculating Magnification - Celestron AstroMaster LT Instruction Manual

To align the Star Pointer finderscope:
1. To turn on the Star Pointer, turn the switch to the "on" position – see Figure 3-4.
2. Locate a bright star or planet and center it in a low power eyepiece in the main telescope.
3. With both eyes open, look through the glass window at the alignment star.
If the Star Pointer is perfectly aligned, you will see the
red LED dot overlap the alignment star. If the Star Pointer
is not aligned, take notice of where the red dot is relative
to the bright star.
4. Without moving the main telescope, turn the Star
Pointer's two adjustment screws until the red dot is
directly over the alignment star. Experiment as to which
way each screw moves the red dot.
5. The Star Pointer is now ready for use. Always turn
the power off after you have found an object. This
will extend the life of both the battery and the LED.
Note: Your battery may be installed already. If not, open the
battery compartment – see Figure 3-4 with a thin coin or
screwdriver. Put the battery in with the "+" sign facing out.
Then put the battery compartment back on. If you ever need
to replace the battery, it is a 3-volt lithium type # CR 1620.
Note: The above description applies basically for astronomy. If your finderscope
is aligned properly, you can use it for terrestrial applications also. The finderscope
acts like a sighting tube. The red dot may be difficult to see in the daytime but the
dot will let you align objects before looking through the main telescope optics and
can be quite helpful.

CALCULATING MAGNIFICATION

You can change the power of your telescope just by changing the eye-
piece (ocular). To determine the magnification of your telescope, simply
divide the focal length of the telescope by the focal length of the eyepiece
used. In equation format, the formula looks like this:
Magnification =
Let's say, for example, you are using the 20mm eyepiece that came with your telescope. To determine the
magnification you simply divide the focal length of your telescope (the AstroMaster LT 60AZ for this example
has a focal length of 700mm) by the focal length of the eyepiece, 20mm. Dividing 700 by 20 yields a magnifi-
cation of 35 power.
Although the power is variable, each instrument under average skies has a limit to the highest useful mag-
nification. The general rule is that 60 power can be used for every inch of aperture. For example, the Astro-
Master LT 60AZ is 2.4" inches in diameter. Multiplying 2.4 by 60 gives a maximum useful magnification of
144 power. Although this is the maximum useful magnification, most observing is done in the range of 20 to
35 power for every inch of aperture which is 48 to 84 times for the AstroMaster LT 60AZ telescope. You can
determine the magnification for your telescope the same way.
Focal Length of Telescope (mm)
Focal Length of Eyepiece (mm)
Battery
Compartment
On/Off
Switch
11
Figure 3-4
Figure 3-5