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Altitude side bearing
Screw w/round knob
Spring
Phillips head
screw (black)
Pull loop
Figure 13.
Close-up view of the CorrecTension system.
panel of the base you will notice two predrilled starter holes,
about 6" apart. Take the black wood screws and thread them
into the starter holes with a Phillips screwdriver. Then you can
"keyhole" the eyepiece rack onto the wood screws and con-
tinue tightening the screws (Figure 11). If you want to be able
to remove the rack, do not tighten the screws too tightly. Be
certain the screws are loose enough so you can lift the rack
and remove it from the screws through the larger part of the
keyhole. If you want to have the rack permanently attached,
thread the screws tightly.
Placing the Optical Tube on the Dobsonian Base
Lift the optical tube and set the altitude bearings on either side
of the tube in the "cradle" of the base (Figure 12). The unique
flange design of the altitude bearing allows for automatic left-
to-right centering of the optical tube in the cradle. Once in the
cradle, the tube should pivot freely up and down with gentle
hand pressure. Note that the tube will not yet be properly bal-
anced, since the eyepiece and finder scope are not in place,
and the CorrecTension system has not been installed.
Installing the CorrecTension (XT)
Friction Optimization System
Perhaps the most exciting new feature of the SkyQuest XT12
Dobsonian is the CorrecTension Friction Optimization sys-
tem. Because of their relatively light weight, 12" and smaller
Dobsonians have always been plagued by insufficient friction
on the altitude bearing surfaces. As a result, such telescopes
move up and down much too freely. This causes problems
when the observer tries to accurately center and track an
object for viewing, especially at higher powers. Also, the tele-
scope becomes very sensitive to balance, requiring additional
equipment such as counterweight systems or adjustable side
bearings to compensate.
SkyQuest XT12 Dobsonians employ a simple yet effective
remedy for the friction problem that obviates the need for
such cumbersome countermeasures. CorrecTension Friction
Optimization utilizes a spring coil to "pull" the tube assem-
bly down onto the altitude bearing pads, thereby increasing
the friction by just the right amount. With CorrecTension, you
can change eyepieces or add a barlow lens without having
to tediously adjust the telescope's balance as you would with
Black nylon
spacers
1/4" washer
(black)
a.
b.
Figure 14.
with your index finger and pull down on the spring. (b) While pulling
down, slip the end ring of the spring over the screw head and onto the
narrow part of the nylon spacer, then release the pull loop.
other Dobsonians. The altitude friction will roughly equal the
azimuth friction, ensuring optimal performance.
To install the CorrecTension assembly, follow these steps
while referring to Figure 13:
1. Put one of the black nylon spacers on a black Phillips head
screw. The spacer should be oriented so the narrow end
seats against the head of the screw. Slip one of the black
1/4" washers over the end of the screw. Now, thread the
screw into the hole in the base side panel just below the
cradle. The screw will thread into the preinstalled insert in
the hole. Use a Phillips screwdriver to tighten the screw.
Repeat this procedure on the opposite side panel.
2. Next, insert one of the screws with round plastic knob
attached through the end ring of one of the springs. Slip
a black nylon spacer onto the screw. Orient the spacer so
the narrow end is closest to the knob. Thread the entire
assembly into the hole in the center of the telescope's alti-
tude side bearing until tight. The end ring of the spring
(a) To attach the spring to the base, grip the pull loop
7
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