Orion STARBLAST 6/6I - Manual (Page 29)

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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 day-
light, preferably in a brightly lit room and aimed at a white wall.
It is recommended that the telescope tube be oriented hori-
zontally. 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. The paper will provide a bright “back-
ground” when viewing into the focuser.
aligning the Secondary Mirror
To adjust the secondary mirror collimation, you will need a
Phillips screwdriver and a 2mm hex key, or Allen wrench.
You will need to check, and adjust if necessary, four aspects of
the secondary mirror’s alignment:
The secondary mirror’s axial position 1.
The secondary mirror’s radial position 2.
The secondary mirror’s rotational position 3.
The secondary mirror’s tilt 4.
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 opening
or toward the rear of the telescope, as it is in
Figure 27b, you
will have to adjust the mirror’s axial position.
To do so, use the 2mm hex key to loosen the three small align-
ment 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 Phillips head screwdriver with
your other hand (
Figure 29). 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 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 fine for
now. Then, tighten the three small alignment set screws equal-
ly 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 adjusting,
or if it does, you’ll typically need to do it only once.
By “radial position” we mean the position of the secondary mir-
ror along the axis perpendicular to the focuser drawtube, as
shown in
Figure 30. This position is changed by adjusting two
of the spider vane thumb nuts, as shown. Loosen one thumb
nut, then tighten the opposite one until the secondary mirror
is centered radially in the drawtube. Do not loosen the thumb
nuts too much, to avoid having them completely unthread from
the ends of the spider vanes. Also, when making this adjust-
ment, be careful not to stress the spider vanes or they could
bend.
adjusting the Secondary Mirror’s
Rotational Position
The secondary mirror should face the focuser squarely. If the
mirror appears to be rotated away from the focuser, the mir-
ror’s rotational position will need to be adjusted. Again, this
adjustment will rarely, if ever, need to be done.
Grip the sides of the secondary mirror holder with your fingers.
Then, using a Phillips screwdriver, loosen the center screw
Figure 30. To center the secondary mirror radially in the
focuser drawtube, make adjustments to the two knurled
spider vane thumbnuts that are perpendicular to the focuser.
Figure 29. 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 head
screwdriver. Do not touch the mirror’s surface.
Spider vane
thumb nuts