reflections for the time being. The secondary mirror itself
should be centered 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. (It helps to adjust the secondary mir-
ror in a brightly lit room with the telescope pointed toward a
bright surface, such as white paper or a wall.) Loosen the
three small alignment screws in the center hub of the sec-
ondary mirror holder several turns. Now hold the secondary
mirror holder stationary (be careful not to touch the surface of
the secondary mirror!), while turning the center Phillips head
screw (as in Figure 15). Turning the bolt clockwise will move
the secondary mirror toward the front opening of the optical
tube, while turning the bolt counter-clockwise will move the
secondary mirror toward the primary mirror.
When the secondary mirror is centered in the focuser draw-
tube, rotate the secondary mirror holder slightly until the
reflection of the primary mirror is as centered in the second-
ary mirror as it will get. It still may not be perfectly centered,
but that is OK. Now tighten the three alignment screws to
secure the secondary mirror in that position. This adjustment
will rarely need to be done, if ever.
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
of the secondary mirror. This is done by alternately loosening
one of the three alignment screws while tightening the other
two, as depicted in Figure 16. The goal is to center the pri-
mary mirror reflection in the secondary mirror, as in Figure
14d. Don’t worry that the reflection of the secondary mirror
(the smallest circle, with your eye reflected in it) 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 14d, the secondary mirror
is centered under the focuser and the reflection of the pri-
mary mirror is centered in the secondary mirror, but the
small reflection of the secondary mirror (with your eye
inside) is off-center.
The tilt of the primary mirror is adjusted with three spring-
loaded collimation thumb screws on the back end of the
optical tube (bottom of the primary mirror cell); these are the
larger thumb screws. The other three smaller thumb screws
lock the primary mirror’s position in place; these thumb
screws must be loosened before any collimation adjustments
can be made to the primary mirror.
To start, unthread the thumb screws that lock the primary mir-
ror in place a few turns each (Figure 17). The thumb screws
are slotted, so if they are too difficult to loosen with your fin-
gers, use a flat-head screwdriver.
Now, try tightening or loosening one of the spring-loaded col-
limation thumb screws one turn (Figure 18). Look into the
focuser and see if the secondary mirror reflection has moved
closer to the center of the primary mirror reflection. Repeat
this process on the other two collimation thumb screws, if
11
Figure 15. 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!
Figure 16
: Adjust the tilt of the secondary mirror by loosening
or tightening the three alignment screws with a Phillips
screwdriver.
Figure 17:
The three thumb screws that lock the primary
mirror in place must first be loosened before any
adjustments can be made.
Figure 18:
The tilt of the primary mirror is adjusted by turning
one or more of the three spring-loaded collimation thumb
screws.
