14
NOTE:
Precise collimation is best achieved by using an
optional collimating tool, such as a quick-collimation cap,
a Cheshire eyepiece, or a laser collimator. Check our web-
site for available collimating tools.
Figures 22b through 22d
assume that you have an optional Cheshire eyepiece or col-
limation cap in the focuser.
Primary Mirror Center Mark
You may have noticed that your SpaceProbe II 76mm reflec-
tor has a tiny ring (sticker) in the exact center of the primary
mirror. This “center mark” allows you to achieve a very pre-
cise collimation of the primary mirror; you don’t have to guess
where the center of the mirror is, which is important in the
collimation process. This center mark is especially useful
when using an optional collimating device, such as Orion’s
LaserMate Deluxe II laser collimator.
NOTE:
The center ring sticker should not be removed from
the primary mirror. Because it lies directly in the shadow of
the secondary mirror, its presence in no way adversely affects
the optical performance of the telescope or the image qual-
ity. That might seem counter-intuitive, but it’s true! Leave it in
place.
Aligning the Secondary Mirror
Align the secondary mirror first. Look down the focuser at the
secondary (diagonal) mirror. If the entire primary mirror reflec-
tion is not visible in the secondary mirror, as in
Figure 22b,
you will need to adjust the tilt of the secondary mirror. This is
done by alternately loosening one of the three
secondary mirror alignment screws with a Phillips screwdriver
then tightening the other two (
Figure 23). The goal is to cen-
ter the primary mirror reflection in the secondary mirror, as
in
Figure 22c. Don’t worry that the reflection of the second-
ary mirror (the smallest circle) is off-center. You will fix that
in the next step. It will take some trial and error to determine
which screws to loosen and tighten to move the reflection of
the primary mirror to the center of the secondary mirror. But
bepatient and you’ll get it.
Aligning the Primary Mirror
The final adjustment is made to the primary mirror. It will need
adjustment if, as in
Figure 22c, the reflection of the primary
mirror is centered in the secondary mirror, but the small reflec-
tion of the secondary mirror is off-center. The tilt of the primary
mirror is adjusted using the three pairs of collimation screws
on the back end of the optical tube (
Figure 24). Adjusting
the tilt of the mirror requires a “push-pull” technique involving
adjustment of one or more pairs of collimation screws.
With a Phillips screwdriver, loosen one of the screws one full
turn, and then tighten the adjacent screw (the one right next
to it) until it is tight. Look into the focuser and see if the sec-
ondary mirror reflection has moved closer to the center of the
primary. You can tell this easily by simply watching to see if
the “dot” of the Cheshire eyepiece or collimation cap is mov-
ing closer or farther away from the ring on the center of the
primary mirror. Repeat this process on the other two sets of
collimation screws, if necessary. Again, it will take a little trial
and error to get a feel for how to tilt the mirror in this way.
When you have the dot centered as much as possible in the
ring, your primary mirror is collimated. The view through the
collimation cap should resemble
Figure 22d. Make sure all
the collimation screws are tight (but do not overtighten), to
secure the mirror tilt. A simple star test will tell you whether the
optics are accurately collimated.
Star-Testing the Telescope
When it is dark, point the telescope at a bright star and accu-
rately center it in the eyepiece’s field of view. Slowly de-focus
the image with the focusing knob. If the telescope is correct-
ly collimated, the expanding disk should be a perfect circle
(
Figure 25). If the image is unsymmetrical, the scope is out
of collimation. The dark shadow cast by the secondary mir-
Figure 23.
Adjust the tilt of the secondary mirror by adjusting
the three alignment screws with a Phillips screwdriver.
Figure 24.
Align the primary mirror by adjusting the three pairs
of “push/pull” screws on the back end of the optical tube.