7
one by one until the collimation eyepiece’s black dot is centered
in the dark ring of the secondary mirror. The correct alignment
of the secondary mirror is critical in determining if the optical
axis requires alignment. Be sure you have properly aligned the
secondary mirror before proceeding to the next step.
Optical Axis (Primary Mirror) Adjustment
The optical axis is denoted by a thin outline of light (white)
around the perimeter of the view through the collimation cap or
Cheshire eyepiece
(Figure 8A)
. If this outline is not a perfect
circle of uniform thickness, as in
8C
, that’s an indication that the
optical axis (primary mirror) needs adjustment. This adjustment
will require 3mm and 2.5mm hex keys.
Note that there are three pairs of screws on the rear cell of the
optical tube where the focuser attaches
(Figure 10)
. Each
pair consists of a small black screw and a larger chrome screw.
The small black screws are merely locking screws, which you
should loosen before adjusting the mirror’s tilt. The larger
chrome screws are spring-loaded collimation screws that actu-
ally adjust the tilt of the primary mirror. Turn these collimation
screws only a fraction of a turn at a time. Turn one and check
the view through the Cheshire to see if it improved the white
optical axis ring. Keep tweaking the collimation screws, each
time checking the optical axis ring, until it is concentric and uni-
form in width. Then tighten the three lock setscrews to fix the
mirror in that position.
After adjusting the optical axis, re-check the collimation of the
secondary mirror and make any necessary adjustments, then
recheck the optical axis collimation. Optical axis collimation will
not need to be performed very often, if ever.
Star Testing
A star test can be performed to confirm the collimation accuracy
of the telescope. The adjustment procedure on the telescope is
the same as described above; testing, however, will be done in
the night sky using a real star and you will not use the collima-
tion cap or Cheshire eyepiece.
Choose a star close to the zenith (straight overhead) rather
than at the horizon to minimize atmospheric distortions. Using
Polaris as your target star can be helpful as minimal drift adjust-
ments will be required.
It is recommended that you not use a star diagonal while per-
forming this procedure. Rather, place an eyepiece directly into
the 1.25
"
adapter in the focuser. It should be an eyepiece that
provides moderate to high magnification. You may need to add
all three of the extension rings in front of the focuser to be able
to reach focus. Center the star in the field of view. Slowly de-fo-
cus the image with the focusing knob until you can see a series
of concentric diffraction rings form around the dark disk in the
center. That dark disk is the shadow of the secondary mirror. In
a well collimated telescope, the diffraction rings should appear
round and concentric, with the dark disk exactly in the center
(Figure 11)
. If the dark central disk is off center, the scope is
out of collimation. Adjust the collimation of the secondary mirror
and, only if necessary, the primary mirror while monitoring the
defocused star until the dark central disk is exactly centered in
the diffraction rings.
NOTE:
It is important when checking or adjusting the
collimation using a star, that the star be positioned in the
center of the eyepiece’s field of view. If it isn’t, the optics
will always appear out of collimation, even though they
may be perfectly aligned! It is critical to keep the star cen-
tered, so over time you may need to make slight correc-
tions to the telescope’s position.
Care and Cleaning of the
Optics
Do not disassemble the telescope, including to clean the mirror.
A small amount of dust and particulates on the mirrors’ surfaces
will not affect performance. In the event internal cleaning is nec-
essary the telescope should be shipped to Orion Telescopes &
Binoculars for service. This telescope does not contain user-ser-
viceable parts and disassembly of the components will void the
warranty. When not in use, please use the supplied dust cap(s)
to keep dust and particulates out of the tube and off the optics.
Chrome
Collimation
screw
Black lock
screw
Figure 10.
Three pairs of collimation screws on the rear cell allow
adjustment of the optical axis, if needed.
Figure 12.
A de-focused view of a bright star through an
eyepiece. Proper collimation will show concentric, symmetrical
diffraction rings with a dark spot exactly in the center, as in
the image on the right. If the spot is off-center, the scope needs
collimation.
Out
of
collimation
Collimated
