Telescope Care And Maintenance - Orion Observer 90mm Instruction Manual

be checked occasionally. With practice, collimating is relative-
ly easy to do and can be done in daylight.
If you purchased the Observer 90mm EQ Refractor, your tele-
scope's lens optics were collimated at the factory and will not
need further adjustment. Reflector telescopes, on the other
hand, need occasional optical collimation as the mirrors can
come out of alignment.
It helps to perform the collimation procedure in a brightly lit
room with the telescope pointed toward a bright surface, such
as a light-colored wall. Placing a piece of white paper inside
the telescope tube opposite the focuser (i.e., on the other side
of the secondary mirror from the focuser) will also be helpful
(Figure 21). You will need a Phillips screwdriver to adjust the
mirrors.
To check your telescope's collimation, remove the eyepiece
and look down the focuser. You should see the secondary
mirror centered in the focuser, as well as the reflection of
the primary mirror centered in the secondary mirror, and the
reflection of the secondary mirror (and your eye) centered in
the reflection of the primary mirror, as in Figure 22A. Got all
that? Review it again carefully, and compare what you see to
Figure 22A. If anything is off-center, proceed with the follow-
ing collimation procedure.
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 website
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 Observer 114mm or 134mm
Reflector has a small ring (sticker) in the exact center of the
primary mirror. This "center mark" allows you to achieve a very
precise 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.
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 21). 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
14
the primary mirror to the center of the secondary mirror. But
be patient 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 prima-
ry mirror is centered in the secondary mirror, but the small
reflection of the secondary mirror is off-center. The tilt of the
primary mirror is adjusted using the three pairs of collimation
knobs and lock screws on the back end of the optical tube
(Figure 23). Each pair consists of a collimation knob and a
small Phillips head lock screw.
First use the screwdriver to loosen the three lock screws a
turn or so. Then tighten one of the collimation knobs about
a quarter turn, then look down the focuser to see if the sec-
ondary mirror reflection has moved closer to the center of the
primary. If it moved farther away then try loosening the same
collimation knob a bit. Repeat this process on the other two
sets of collimation screws, if necessary, adjusting them one
way or the other and seeing if the secondary mirror reflection
moves closer to the center of the primary mirror reflection. It
will take a little trial and error to get a feel for how to tilt the mir-
ror in this way. When the center hole in your collimating tool is
centered as much as possible on the reflection of the adhe-
sive dot on the primary mirror, your primary mirror is colli-
mated. The view through the collimation cap should resemble
Figure 22D. Then, very lightly tighten the three lock screws
so that the primary mirror stays in that position. 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 24). If the image is unsymmetrical, the scope is out
of collimation. The dark shadow cast by the secondary mir-
ror should appear in the very center of the out-of-focus circle,
like the hole in a donut. If the "hole" appears off-center, the
telescope is out of collimation. If you try the star test and the
bright star you have selected is not accurately centered in
the eyepiece, the optics will always appear out of collimation,
even though they may be perfectly aligned. It is critical to keep
the star centered, so over time you will need to make slight
corrections to the telescope's position in order to account for
the sky's apparent motion.
VII. Telescope Care and
Maintenance
If you give your telescope reasonable care, it will last a life-
time. Store it in a clean, dry, dust free place, safe from rapid
changes in temperature and humidity. Do not store the tele-
scope outdoors, although storage in a garage or shed is OK.
Small components like eyepieces and other accessories
should be kept in a protective box or storage case. Keep the
caps on the front of the telescope and on the focuser draw-
tube when not in use.