Celestron STARSENSE EXPLORER 8 DOBSONIAN Manuel D'instructions page 11

DETERMINING MAGNIFICATION
AND SELECTING EYEPIECES
To change the magnifi cation of the telescope, you'll need
to change the eyepiece in the telescope's focuser. To
calculate the magnifi cation you can achieve with a given
eyepiece, use this formula:
Focal length of telescope ÷
Focal length of eyepiece
= Magnifi cation
The 8" and 10" SSE Dobs have a focal length of 1200mm
and come with a 25mm Omni Plössl eyepiece. Using the
formula, we can calculate that this combination yields
a magnification of 48x (1200mm ÷ 25mm = 48x). The
12" SSE Dob has a focal length of 1500mm and comes
with a 32mm Omni Plössl eyepiece – this provides a
magnification of 47x (1500mm ÷ 32mm = 47x). This
is an excellent magnification for locating and observing
wide-field deep space objects. You may want to consider
purchasing a higher-magnifi cation eyepiece, like a 10mm
Omni Plössl, for higher-power views of the Moon and
planets. Do not increase magnifi cation too much though, or
the view may degrade due to atmospheric seeing conditions
(i.e. air turbulence).
The maximum magnifi cation for any telescope is about 60
times per inch, which equates to 480x for the 8" SSE Dob,
600x for the 10" SSE Dob , and 720x for the 12" SSE Dob.
In many locations, however, it will be diffi cult to achieve sharp
images much over 100x magnifi cation due to turbulence in
the air above you. If you notice that the stars overhead are
twinkling heavily, seeing conditions are poor. You should stick
to lower magnifi cation. If the stars appear to shine steadily,
seeing conditions are good. You can try using higher-
magnifi cation eyepieces.
The SSE Dobs can accept both 1.25" and 2" format
eyepieces. 2" eyepieces generally provide a wider fi eld of
view but can cost signifi cantly more. To use a 2" eyepiece,
remove the 2"-to-1.25" adapter from the focuser and insert
the eyepiece directly into the 2" extension tube. Secure the
eyepiece with the thumbscrews on the 2" extension tube.
The eyepiece rack located on the front of the base provides a
convenient place to put eyepieces when they are not in use.
It can accept three 1.25" eyepieces and one 2" eyepiece
(Figure 13).
Figure 13: The eyepiece rack is a convenient place to store additional
eyepieces during your observing session.
COOLING YOUR
TELESCOPE'S OPTICS
You'll get the best views through your telescope when it
has reached thermal equilibrium with the ambient air. If
the telescope is warmer than the outside air, the mirror
will acclimate to the temperature and its fi gure will be
changing. The images you see through a telescope that
has not cooled will not appear as sharp as they otherwise
would. If you are taking your telescope from a heated house
to the outdoors, allow around one hour before expecting it
to produce sharp images. For this reason, we recommend
storing your telescope in a dry but unheated area like a
garage or storage shed. We also recommend taking the
telescope out at sunset, so it will already be acclimated
by the time it gets dark.
For the 10" and 12" SSE Dobs, there is an optional USB
Cooling Fan for Dobsonians available. It mounts onto the rear
of the mirror cell and blows air on the mirror to expedite cool-
ing (Figure 14). The fan will help the optics reach thermal
equilibrium faster. (The 8" SSE Dob does not have a fan
mount so it is not compatible with the Cooling Fan.)
Figure 14: The optional USB Cooling Fan for Dobsonians is compatible with
the 10" and 12" SSE Dobs.
ENGLISH I 11