Telescope Basics; Focusing; Calculating Magnifi Cation; Installing & Using The Barlow Lens - Celestron TRAVEL SCOPE 70 Manuel D'instructions

TELESCOPE BASICS

FOCUSING

To focus your Travel Scope turn the focus knob located near the rear of the telescope (see Figure 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 (specifi cally 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.
CALCULATING MAGNIFICATION
You can change the power of your telescope just by changing the eyepiece (ocular). To determine the magnifi cation 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)
_____________________________
Magnifi cation =
Focal length of Eyepiece (mm)
Let's say, for example, you are using the 20mm eyepiece that came with your Travel Scope 70 telescope. To determine the
magnifi cation 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 magnifi cation of 20x.
Although the power is variable, every telescope under average skies has a limit to the highest useful magnifi cation. The
general rule is that 60 power can be used for every inch of aperture. For example, the Travel Scope 70 is 2.8" inches in
diameter. Multiplying 2.8 by 60 gives a maximum useful magnifi cation of 168 power. Although this is the maximum useful
magnifi cation, 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 magnifi cation.
When using the 8mm eyepiece together with the 3x Barlow lens with the Travel Scope 50 gives extremely high power and
can be used on rare occasions – you will achieve the power but the image will be dark with low contrast because you have
magnifi ed it to the maximum possible. For the brightest images with the highest contrast levels, use lower powers.
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.
INSTALLING AND USING THE BARLOW LENS (TRAVEL SCOPE 50 ONLY)
Your telescope also comes with a 3x Barlow Lens
which triples the magnifying power of each eyepiece.
However, the greatly magnifi ed images should only
be used under ideal conditions – see the Calculating
Magnifi cation section of this manual. To use the
Barlow lens remove the diagonal and insert the
Barlow directly into the focuser tube. You then insert
an eyepiece into the Barlow lens for viewing.
3x Barlow Lens
Note: Start by using a low power eyepiece as it will
Fig. 13
be easier to focus.
10 I ENGLISH