Celestron 21035 User Manual
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To focus your Travel Scope turn the focus knob located near the rear of the telescope (see Figure 1-1). Turning the
knob counterclockwise allows you to focus on an object that is farther than the one you are currently observing.
Turning the knob clockwise from you allows you to focus on an object closer than the one you are currently
observing.
Note:
Remove the front lens cap of the Travel Scope optical tube prior to attempting your observation.
Note:
If you wear corrective lenses (specifically glasses), you may want to remove them when observing with an
eyepiece attached to the telescope. If you have astigmatism, corrective lenses should be worn at all times.
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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 divide the focal length of your telescope (the Travel Scope for this example has a focal length of
400mm) by the focal length of the eyepiece, 20mm. Dividing 400 by 20 yields a magnification of 20x.
Although the power is variable, every telescope 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 Travel Scope 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 of your observing will be done at low powers which generate brighter and
sharper images.
Note on Using High Powers – Higher powers are used mainly for lunar and sometimes planetary observing where
you can greatly enlarge the image, but remember that the contrast and brightness will be very low due to the high
magnification.
You can purchase optional eyepieces to give you a range of powers you can observe with. Visit the Celestron
website to see what is available.