Celestron C21061 Calculating Magnification, Focal Length of Telescope mm, Battery Compartment

Battery Compartment	On/Off
	Switch

Figure 3-4 Figure 3-5

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 eyepiece (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:

Focal Length of Telescope (mm)

Magnification = ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

Focal Length of Eyepiece (mm)

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 70AZ for this example has a focal length of 900mm) by the focal length of the eyepiece, 20mm. Dividing 900 by 20 yields a magnification of 45 power.

Although the power is variable, each instrument under average skies has a limit to the highest useful magnification. The general rule is that 60 power can be used for every inch of aperture. For example, the AstroMaster 70AZ is 2.8” inches in diameter. Multiplying 2.8 by 60 gives a maximum useful magnification of 168 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 56 to 98 times for the AstroMaster 70AZ telescope. You can determine the magnification for your telescope the same way.

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