Orion #8297 8" F/3.9 - Manual (Page 3)

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packaging to ensure the telescope stays intact during shipping.
Take a moment to inspect the telescope and all of its parts.
Before proceeding with the instructions, refer to Figure 1
to familiarize yourself with some of the features and com­
ponents of the telescope.
1. Getting Started
The telescope arrives nearly fully assembled from the factory,
with optics installed, in a single shipping box. The optics were
collimated at the factory, however you should check the col-
limation prior to first use (see “Collimating the Optics”), as it’s
not uncommon for Newtonian optics to get bumped slightly
out of collimation in the delivery process. Likely only a minor
adjustment, if any, may be necessary.
Attaching the Telescope to a Mount
The f/3.9 Newtonian Astrographs each come with a pair of
hinged, felt-lined tube rings to hold the optical tube assembly
(OTA) on a mount. Each ring has a flat boss on opposing sides.
Both bosses have a ¼"-20 threaded hole in the center. One
tube ring has a piggyback camera adapter mounted on one
of the bosses, which can be used to mount a camera for pig-
gyback astrophotography. That adapter can be removed if you
wish to attach an optional dovetail plate to the top of the tube
rings for mounting a piggybacked guide scope.
The tube rings should be attached to a dovetail mounting
plate (sold separately) compatible with your mount’s equa-
torial head. Balancing the telescope is achieved by sliding
the dovetail mounting plate forward or backward within the
mount’s dovetail saddle. You can also move the telescope
forward or backward within the tube rings. To do so, loosen
the tube ring clamps slightly and slide the telescope tube
forward or backward as needed to reach optimum balance,
then retighten the clamps. Rotating the telescope to achieve
a comfortable eyepiece or camera angle is done in the same
fashion. Simply loosen the tube ring clamps just enough to
allow the optical tube to rotate within the tube rings. Retighten
the tube ring clamps securely once you have reached the
desired eyepiece or camera orientation.
2" Dual-Speed Crayford Focuser
The f/3.9 Newtonian Astrograph features an all-metal, 2"
dual-speed (11:1) Crayford-type focuser
(Figure 2), which
allows very precise, fine focusing. A reinforcing plate inside
the optical tube just under the focuser provides added rigidity,
minimizing any “flexing” of the focuser housing on the tube
due to the weight and moment arm of the imaging camera. If
the drawtube slips under the weight of your imaging system or
heavy visual accessories, simply increase the drawtube ten-
sion by gently tightening the drawtube tensioning thumbscrew
as needed.
The smooth focus motion and fine-focus wheel allow preci-
sion adjustments for critical focusing of eyepieces and camer-
as. Once focus is reached, you can lock the drawtube in place
by tightening the drawtube tensioning thumbscrew.
The focuser drawtube has a 2" collar on the end of it, with two
thumbscrews, for attachment of 2" accessories. The telescope
ships with a 1.25" eyepiece holder inserted into the 2" collar.
The focuser drawtube has 38mm of travel.
Fine Focus
The dual-speed Crayford focuser features both coarse and
fine focusing wheels. The two large, silver-colored wheels are
for coarse focusing. The small black wheel next to the right-
hand large focus wheel allows ultra-precise focus adjustment
at a gear ratio of 11:1, meaning eleven turns of the fine focus
wheel equals one turn of the large focus wheel.
Use the large focus wheels to achieve rough focus on your
target object, then use the fine focus wheel to home in on the
exact focus point. You will be amazed at the amount of detail
that careful fine focus adjustment brings in to view on targets
such as the lunar surface, planets, double stars, and other
celestial objects.
Focuser Reinforcing Plate
You’ll notice that on the inside of the optical tube directly under
the focuser is a steel reinforcing plate. This plate was added to
provide extra rigidity to the interface between the focuser and
tube, to minimize the possibility of flexure at that interface due
to the weight of the imaging camera and its positional moment
arm. Such flexure could cause undesirable distortion in long-
exposure astrophotographic images. This reinforcing plate
allows use of heavier cameras while minimizing the risk of flex-
ure between the focuser base and tube. It is a design enhance-
ment that other, similar scopes on the market do not have.
1.25" Eyepiece holder Accessory lock
thumbscrews
2"
Accessory
collar
Coarse focus wheels
Drawtube
tensioning
thumbscrew
Eyepiece lock
thumbscrews
Figure 2. The 2" dual-speed (11:1) Crayford focuser
11:1
Fine
focus
wheel