Table of Contents
Advertisement
Figure 20.
To center the secondary mirror under the focuser, hold
the secondary mirror holder in place with your fingers while adjusting
the center screw with a Phillips screwdriver. Do not touch the mirror's
surface!
has a hole in the center and a silver bottom. This helps center
your eye so that collimation is easy to perform. Figures 19b
through 19e 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
simply adjust the mirror position (described below) until the
reflection 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
telescope 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 19b, 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 col-
limating the secondary mirror. Using a 2mm hex key, loosen
the three small alignment set screws in the center hub of the
4-vaned spider several turns. Now hold the mirror holder sta-
tionary (be careful not to touch the surface of the mirrors),
while turning the center screw with a Phillips head screw-
driver (See Figure 20). Turning the screw clockwise will move
the secondary mirror toward the front opening of the optical
12
Figure 21.
Adjust the tilt of the secondary mirror by loosening or
tightening the three alignment screws with a 2mm hex key.
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.
If the entire primary mirror reflection is not visible in the sec-
ondary mirror, as in Figure 19c; you will need to adjust the tilt
of the secondary mirror. This is done by alternately loosening
one of the three alignment set screws while tightening the
other two, as depicted in Figure 21. The goal is to center the
primary mirror reflection in the secondary mirror, as in Figure
19d. Don't worry that the reflection of the secondary mirror
(the smallest circle, with the collimation cap "dot" in the cen-
ter) is off-center; you will fix that in the next step.
Adjusting the Primary Mirror
The final adjustment is made to the primary mirror. It will need
adjustment if, as in Figure 19d, the secondary mirror is cen-
tered under the focuser and the reflection of the primary mirror
is centered in the secondary mirror, but the small reflection of
the secondary mirror (with the "dot" of the collimation cap) is
off-center.
The tilt of the primary mirror is adjusted with three spring-
loaded collimation thumbscrews on the back end of the
optical tube (bottom of the primary mirror cell); these are the
larger thumbscrews. The other three smaller thumbscrews
lock the mirror's position in place; these thumbscrews must
be loosened before any collimation adjustments can be made
to the primary mirror.
To start, turn the smaller thumbscrews that lock the primary
mirror in place a few turns each (Figure 22). Use a screw-
driver in the slots, if necessary.
Advertisement
Table of Contents
