19
If a clutch tension it is set too loose, the scope may not slew
on that axis, or may slew intermittently. In that case you
should tighten the clutch knob(s) a little until a normal slewing
motion is achieved. If you add significant weight to the front of
the telescope, such as a heavy eyepiece and finder scope or
a full-aperture glass solar filter, the scope could become “front
heavy.” In that case you may have to tighten the altitude clutch
knob some so that the tube doesn’t slip when moving in the
up/down direction.
Focusing the telescope
The SkyQuest XXg Dobsonians come standard with a 2"
dual-speed (11:1) Crayford focuser (
Figure 27). The focuser
has coarse focus knobs and a fine focus (11:1) knob for very
precise focusing. The focuser allows use of 2" or 1.25" eye-
pieces and the Crayford design prevents image shift while
focusing.
To focus, with an eyepiece in the focuser and secured with the
thumbscrews, move the telescope so the front end is pointing
in the general direction of an object at least 1/4-mile away.
Now, with your fingers, slowly rotate one of the coarse focus
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’re
close to the focus point.
Now, use the fine focus knob to achieve precise focus. Eleven
turns of the fine focus knob are equivalent to one turn of the
coarse focus knobs, so much finer adjustment is possible
than with just the coarse focus knobs alone. You’ll find this is
a great convenience, especially when attempting to focus at
high magnifications. If you have trouble focusing, rotate the
coarse focusing knob so the drawtube is inward as far as it
will go. Now look through the eyepiece while slowly rotating
the focusing knob in the opposite direction. You should soon
see the point at which focus is reached. The thumbscrew on
the bottom of the focuser body
(Figure 27) will lock the fo-
cuser drawtube in place, if desired. This is usually not neces-
sary, however. Before focusing, remember to first loosen this
thumbscrew.
If you find the drawtube tension when focusing is either too
tight (i.e., focus knob is difficult to turn) or too loose (i.e.,
drawtube moves by itself under the weight of the eyepiece),
you can adjust it by tightening or loosening the drawtube ten-
sioning setscrew on the focuser, which is located just below
the focus lock thumbscrew (see
Figure 27). Adjust this set-
screw with the included 2.5mm hex key. Do not loosen the
setscrew too much as there must be some tension to keep the
drawtube secure within the focuser. The other setscrew below
the drawtube tensioning setscrew does not affect drawtube
tension and should not be adjusted.
Figure 34. a)
The redesigned altitude (Alt) and (AZ) azimuth motor/encoder housings of the XXg Dobs feature large manual clutch knobs for
adjustable motion tension.
b)
Rotate the clutch knob to adjust the friction of motion for slewing the telescope by hand.
Alt
AZ
Clutch tensioning knobs
a.
b.
