7. Collimating
(Aligning The Mirrors)
Collimating is the process of adjusting the mirrors so they are
aligned with one another. Your telescope’s optics were aligned
at the factory, and should not need much adjustment unless
the telescope is handled roughly. Accurate mirror alignment is
important to ensure the peak performance of your telescope,
so it should be checked regularly. Collimating is relatively easy
to do and can be done in daylight.
To check collimation, remove the eyepiece and look down the
focuser drawtube. You should see the secondary mirror cen-
tered in the drawtube, 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 14a. If anything is off-cen-
ter, as in Figure 14b, proceed with the following collimating
procedure.
Note About the 2" Focuser
The Atlas 8 EQ’s 2" focuser can be collimated by 3 pairs of
push-pull screws located on the ring at the base of the focuser
(Figure 4). The focuser was collimated at the factory and
should never need to be adjusted. Focuser collimating is only
required under very rare circumstances but has been made
available for this telescope should such a need arise.
The Collimation Cap and Mirror Center Mark
Your Atlas 8 EQ comes with a collimation cap. This is a simple
cap that fits on the focuser drawtube like a dust cap, but has a
hole in the center and a silver bottom. This helps center your
eye so that collimating is easy to perform. Figures 14b through
14e assume you have the collimation cap in place.
In addition to the collimation cap, the primary mirror is marked
with a circle at its exact center. This “center mark” allows you
to achieve a precise collimation of the primary mirror; you
don’t have to guess where the center of the mirror is. You sim-
ply adjust the mirror position (described below) until the reflec-
tion of the hole in the collimation cap is centered in the ring.
The center mark is also required for best results when using
other collimating devices, such as Orion’s LaserMate Laser
Collimator, obviating the need to remove the primary mirror
and mark it yourself.
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 its true!
Aligning the Secondary Mirror
With the collimation 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, in the direction parallel to the
length of the telescope. If it isn’t, as in Figure 14b, it must be
adjusted. This adjustment will rarely, if ever need to be done.
It helps to adjust the secondary mirror in a brightly lit room
with the telescope pointed towards a bright surface, such as
white paper or wall. Also placing a piece of white paper in the
telescope tube opposite the focuser (in other words, on the
other side of the secondary mirror) will also be helpful in colli-
mating the secondary mirror. Using a 2mm hex wrench,
loosen the three small alignment set screws in the center hub
of the 4-vaned spider several turns. Now keep the mirror’s
holder stationary (be careful not to touch the surface of the
mirrors), while turning the center screw with a Phillips head
screwdriver (See Figure 15). 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.
Note: When making these adjustments, be careful not to
stress the spider vanes or they may bend.
When the secondary mirror is centered in the focuser draw-
tube, 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 centered, but that is OK. Now
tighten the three small alignment screws equally to secure the
secondary mirror in that position. This adjustment will rarely, if
ever need to be done.
If the entire primary mirror reflection is not visible in the sec-
ondary mirror, as in Figure 14c; you will need to adjust the tilt
12
Figure 14.
Collimating the optics. (a) When the mirrors are properly aligned, the view down
the focuser drawtube should look like this (b) With the collimation cap in place, if the optics are
out of alignment, the view might look something like this. (c) Here, the secondary mirror is
centered under the focuser, but it needs to be adjusted (tilted) so that the entire primary mirror
is visible. (d) The secondary mirror is correctly aligned, but the primary mirror still needs
adjustment. When the primary mirror is correctly aligned, the “dot” will be centered, as in (e).
a.
b.
c.
d.
e.
