Collimating The Newtonian Reflector - Meade LX70 Series Instruction Manual

Alignment (Collimation) of
the Newtonian Reflector OTA
The optical systems of Newtonian Reflector
telescopes include the following parts: primary
mirror (Fig. 34, #1); secondary mirror (Fig. 34,
#2); secondary mirror-holder (Fig. 34, #3); sec-
ondary mirror-vanes (Fig. 34, #4) and (Fig. 35,
#1); primary mirror-tilt screws (Fig. 34, #5). The
telescope's image is brought to a focus at (Fig.
34, #6).
1. Confirm alignment - To confirm optical
alignment look down the focuser drawtube (Fig.
37, #1) with the eyepiece removed. The edge of
the focuser drawtube frames reflections of the
primary mirror (Fig. 37, #2), the secondary mir-
ror (Fig. 37, #3), the four ("spider") vanes (Fig.
37, #4) holding the secondary mirror, and the
observer's eye (Fig. 37, #5). With the optics
properly aligned, all of these reflections appear
concentric (centered), as shown in Fig. 37. Any
deviation from concentricity of any of these tele-
scope parts with the eye requires adjustments
to the secondary mirror-holder (Fig. 35) and/or
the primary mirror cell (Fig. 36), as described
below.
2. Secondary mirror-vane adjustments: If the
secondary mirror (1, Fig. 38) is left or right of
center within the drawtube (Fig. 38, #2), slightly
loosen the 3 collimation screws on the top of
the secondary mirror holder (Fig. 35, #2). Next,
tighten or loosen as necessary, the central
Phillips screw to center the secondary mirror
position in the focuser draw tube. When cor-
rectly positioned, lightly tighten the 3 collima-
tion screws (Fig. 35, #2) until they touch the top
of the secondary mirror. The secondary mirror
should now be centered in the focuser drawtube
left or right. If the secondary mirror (Fig. 38, #1)
is above- or below-center within the drawtube,
thread inward one of the adjustment/lock knobs
(Fig. 35, #1) while unthreading another of these
knobs. Only make adjustments to two knobs at
a time until the secondary mirror appears as in
Fig. 39.
3. Secondary mirror-holder adjustments: If
the secondary mirror (Fig. 39, #1) is centered
in the focuser drawtube (Fig. 39, #2), but the
primary mirror is only partially visible in the re-
flection (Fig. 39, #3), the three secondary mirror
collimation screws (Fig. 35, #2) should be slight-
ly unthreaded to the point where the secondary
mirror-holder (Fig. 35, #3) can rotate about its
axis parallel to the main tube. Grasp the sec-
ondary mirror-holder (avoid touching the mir-
ror surface!) with your hand and rotate it until,
looking through the drawtube, you can see the
primary mirror centered as well as possible in
the reflection of the secondary mirror. With the
rotation of the secondary mirror-holder at this
best-possible position, thread in the three sec-
ondary collimation screws (Fig. 35, #2) to lock
the rotational position. Then, if necessary, make
adjustments to these three collimation screws
to refine the tilt-angle of the secondary mirror,
until the entire primary mirror can be seen cen-
tered within the secondary mirror's reflection.
With the secondary mirror thus aligned the im-
age through the drawtube appears as in Fig. 40.
4. Primary mirror adjustments: If the second-
ary mirror (Fig. 40, #1) and the reflection of the
primary mirror (Fig. 40, #2) appear centered
within the drawtube (Fig. 40, #3), but the reflec-
tion of your eye and the reflection of the sec-
ondary mirror (Fig. 40, #4) appear off-center,
then the primary mirror tilt requires adjusting,
using the Phillips head screws of the primary
mirror cell (Fig. 36, #3). These primary mirror-tilt
screws are located behind the primary mirror,
at the lower end of the main tube. See Fig. 36.
Before adjusting the primary mirror-tilt screws,
first unscrew by several turns the three long
primary mirror lock screws (Fig. 36, #2) which
are also located on the rear surface of the pri-
mary mirror cell and which alternate around the
cell's circumference with the three long and thin
thumbscrews. These lock screws do not have
springs beneath them. Then by trial and error
turn the primary mirror tilt thumbscrews (Fig. 36,
#3) until you develop a feel for which way to turn
each screw to center the reflection of your eye
in the drawtube. (An assistant is helpful in this
operation.) With your eye centered as shown in
Fig. 37, turn the three long and thin mirror lock
screws (Fig. 36, #2) to re-lock the tilt-angle of
the primary mirror.
5. The telescope's optical system is now aligned,
or collimated. This collimation should be re-
checked from time to time, with small adjust-
ments (per steps 1, 2, and/or 3, above) effected
as required to keep the optics well-aligned.
16 16