8
Figure 12. Altitude and azimuth moving
2.1.2. Selecting an Eyepiece
Always begin viewing with the lowest power eyepiece. (Note: a 20 mm focal length eyepiece has a lower
power than a 12.5 mm one.)
The power or magnification offered by a telescope is determined by two factors: the optical or focal length of
the telescope's lens and the eyepiece's focal length. This telescope's focal length is 700 mm. To calculate
the magnification factor, divide the lens' focal length by that of the eyepiece. The resulting value represents
the magnification factor offered by the telescope when it is used with this eyepiece. For example, using a 20
mm eyepiece provides a magnification factor of:
Magnification = 700 mm/20 mm =
35X
Some words of caution on magnification
. Although the theoretical power or magnification of a telescope
is virtually limitless, there are practical limits, such as he earth's atmosphere. Every telescope has a useful
magnification limit of about 2X per millimeter of aperture. This comes to 140X for a 70mm telescope.
Moderate magnifications are what give the best views. It is better to view a small, but bright and detailed
image than a dim, unclear, oversized image.
2.1.3. Install and Using Barlow Lens
A Barlow lens is used to increase the magnification of each eyepiece. Foe example, the total magnification
will be 105X when a 20mm eyepiece (35X) and a 3X Barlow lens are used together. To use the Barlow lens,
remove the diagonal and insert the Barlow directly into the focuser drawtube. You then insert an eyepiece
into the Barlow lens for viewing. You can also insert the diagonal into the Barlow lens and then use an
eyepiece in the diagonal but you may not be able to reach focus with all eyepieces.
Figure 13. Using Barlow lens
2.1.4. Installing & Using the 1.5x Erecting Eyepiece
The iExplore 70AZ comes with a 1.5x erecting eyepiece, primarily for daytime terrestrial viewing.
This eyepiece produces an image in the eyepiece that is correctly oriented both vertically and horizontally.
Barlow lens
Altitude locking
knob #12
Azimuth locking
knob #13
Altitude adjustment
rod #7
