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Figure 11.
Placing a piece of white paper inside the optical tube
opposite the focuser provides a bright background when viewing into
the focuser.
NOTE: The center ring sticker need not ever 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 tele
scope or the image quality. That might seem counter
intuitive, but it's true!
Preparing the Telescope for Collimating
Once you get the hang of collimating, you will be able to do
it quickly even in the dark. For now, it is best to collimate in
daylight, preferably in a brightly lit room and aimed at a light-
colored wall. It is recommended that the telescope tube be
oriented horizontally. This will prevent any parts from the
secondary mirror from falling down onto the primary mirror
and causing damage if something comes loose while you are
making adjustments. Place a sheet of white paper inside the
optical tube directly opposite the focuser (Figure 11). The
paper will provide a bright "background" when viewing into
the focuser. Just be sure to remove the paper when you're
finished collimating.
Aligning the Secondary Mirror
To adjust the secondary mirror collimation, you will need both
a small and a large Phillips screwdriver.
You will need to check, and adjust if necessary, four aspects
of the secondary mirror's alignment:
1. The secondary mirror's axial position
2. The secondary mirror's radial position
3. The secondary mirror's rotational position
4. The secondary mirror's tilt
8
Figure 12.
To center the secondary mirror axially under the
focuser, hold the secondary mirror holder in place with your
fingers while adjusting the center screw with a large Phillips-head
screwdriver. Later you will adjust the tilt of the secondary mirror
by turning the three small set screws that surround the large
center screw.
The first three will probably only need to be checked and (pos-
sibly) adjusted once. Thereafter, it is usually only the second-
ary mirror's tilt that will need to be adjusted occasionally.
Adjusting the Secondary Mirror's Axial Position
With the collimating cap in place, look through the hole in the
cap at the secondary (diagonal) mirror. Ignore the reflections
for the time being. The secondary mirror itself should be cen-
tered in the focuser drawtube. If it is off-center along the axis
of the telescope, i.e., positioned too far toward the front open-
ing or toward the rear of the telescope, as it is in Figure 9b,
you will have to adjust the mirror's axial position.
To do so, use a small Phillips screwdriver to loosen the three
small alignment set screws in the center hub of the 4-vane
spider several turns. Now, grasp the mirror holder (the cylinder
that is attached to the back of the secondary mirror itself) with
one hand while turning the center screw with a large Phillips
head screwdriver with your other hand (Figure 12). Turning
the screw clockwise will move the secondary mirror toward
the front opening of the optical tube, while turning the screw
counter-clockwise will move the secondary mirror toward the
primary mirror. When the secondary mirror is centered axially
in the focuser drawtube, rotate the secondary mirror holder
until the reflection of the primary mirror is as centered in the
secondary mirror as possible. It may not be perfectly cen-
tered, but that is fine for now. Then, tighten the three small
alignment set screws equally to secure the secondary mirror
in that position.
Adjusting the Secondary Mirror's Radial Position
Like the axial position, the secondary mirror's radial position
was set at the factory and will probably not need any adjust-
ing, or if it does, you'll typically need to do it only once.
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