Orion StarBlast Instruction Manual page 5

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 it's true!
Aligning the Secondary Mirror
It helps to adjust the secondary mirror in a brightly lit room with
the telescope pointed toward a bright surface, such as white
paper or wall. Placing a piece of white paper in the telescope
tube opposite the focuser (i.e. behind the secondary mirror)
will also be helpful in collimating the secondary mirror.
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 isn't, as in Figure 4b, it must
be adjusted. Typically, this adjustment will rarely, if ever, need
to be done.
Note: When make adjustments to the secondary mirror posi-
tion, be careful not to stress the spider vanes, or they may
bend.
To adjust the secondary mirror left-to-right in the focuser draw-
tube, use a 2.5mm hex key to loosen the three small alignment
setscrews in the center hub of the 4-vaned spider several
turns. Now hold the mirror holder stationary (be careful not to
touch the surface of the mirror), while turning the center screw
with a Phillips head screwdriver (Figure 5). 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 left-to-right in
the focuser drawtube, rotate the secondary mirror holder until
the reflection of the primary mirror is as centered in the sec-
ondary mirror as possible. It may not be perfectly centered, but
that is OK for now. Tighten the three small alignment setscrews
equally to secure the secondary mirror in that position.
Figure 5.
To center the secondary mirror under the focuser, hold
the secondary mirror holder in place with your fingers while adjusting
the center screw with the Phillips head screwdriver. Do not touch the
mirror's surface.
To adjust the secondary mirror up-and-down in the focuser
drawtube, adjust the length of the two spider vanes perpen-
dicular to the focuser. This is done by tightening the knurled
thumbnuts that secure the vanes to the tube (Figure 6). Loosen
one thumbnut, then tighten the other until the secondary mirror
is centered in the drawtube.
Spider
vane
thumbnuts
Figure 6.
To center the secondary mirror up-and-down in the
focuser drawtube, make adjustments to the two knurled spider vane
thumbnuts that are perpendicular to the focuser.
The secondary mirror should now be centered in the focuser
drawtube. Now we will shift our attention to the reflections with-
in the secondary mirror.
If the entire primary mirror reflection is not visible in the sec-
ondary mirror, as in Figure 4c, you will need to adjust the tilt
of the secondary mirror. This is done by alternately loosening
one of the three alignment setscrews while tightening the other
two, as depicted in Figure 7. You will need a 2mm hex key to
do this. The goal is to center the primary mirror reflection in the
secondary mirror, as in Figure 4d. Don't worry that the reflec-
tion of the secondary mirror within the primary mirror reflection
(the smallest circle, with the collimation cap "dot" in the center)
is off-center. You will fix that in the next step.
Alignment set
screws (3)
Figure 7.
Adjust the tilt of the secondary mirror by loosening one
of the three alignment set screws then tightening the other two.
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