Focusing The Telescope - Orion 9931 Instruction Manual

Figure 3. Secondary mirror centered under focuser tube,
viewed through the collimating Eyepiece (as are the next
tube and the base. Don't be afraid to load the telescope into
your car for a trip to the hills. Common sense prevails: as long
as the telescope does not bounce around, it won't get dam-
aged in transit.
Naturally, you should be extra careful not to damage any
bearing surface, which could hinder the smooth movement of
the telescope.
Carry the telescope tube and the base separately (make two
trips). The handle on the Dobsonian base provides an easy
grip. While the two components are not terribly heavy, they
are bulky, so use caution to avoid hurting them or yourself. Be
especially careful when passing through doorways with the
optical tube: knocking it against the door frame doesn't do the
optical alignment any good! It is always a good idea to get
someone to help you carry the telescope.
Set-up and Field use
When selecting a location for observing, get as far away as
possible from direct artificial light such as street lights, porch
lights, and automobile headlights. The glare from these lights
will greatly impair your dark-adapted night vision. The tele-
scope should be set up on a relatively level surface for proper
operation of the mount. A grass or dirt surface is preferable to
asphalt, because asphalt radiates more heat, which disturbs
the air and degrades the images.
It's best also to escape the light-polluted city sky in favor of
dark country skies. You'll be amazed at how many more stars
and faint deep-sky objects are visible in dark sky conditions.
two illustrations).
Figure 4. Secondary mirror correctly aligned (tilted).

Focusing the telescope

Insert an eyepiece into the focuser and secure with the
thumbscrew. Look through the eyepiece and get a bright
object in the field of view. Now, with your fingers, slowly rotate
one of the focusing knobs until the object comes into sharp
focus. Go a little bit beyond sharp focus until the image just
starts to blur again, then reverse the rotation of the knob, just
to make sure you hit the exact focus point.
If you have trouble focusing, aim the telescope at a bright
subject at least a few hundred feet away, such as a bright
light. Rotate the focuser fully clockwise so that the drawtube
is in as far as it will go. Now look through the eyepiece while
slowly rotating the focusing knob counterclockwise. You
should soon see the point at which focus is reached.
aligning the Finder Scope
The finder scope and the telescope should be aligned to point
to exactly the same spot in the sky. Alignment is easiest to do
in daylight hours, before your observing session. Choose a
treetop, telephone pole, street sign-anything that is far off in
the distance, at least 200 yards away. Put that image in the
center of the field of your telescope's eyepiece. Where is it in
your finder scope's eyepiece? Hopefully, the image will be in
the field of view and some simple adjustments on the align-
ment screws of the mounting bracket will put the image
dead-center in the crosshairs.
By loosening one alignment screw and tightening another,
you can change the line of sight of the finder scope. Continue
making adjustments to the various alignment screws until the
image in both the finder scope the telescope's eyepiece is
exactly centered. Check the alignment by moving the scope
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