Aligning The Secondary Mirror - Orion starBlast 4.5 EQ Instruction Manual

the collimating cap and Primary
Mirror center Mark
Your StarBlast 4.5 EQ comes with a collimating 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 collimating is easy to perform. Figures 9b through
9e assume you have the collimating cap in place.
In addition to the collimating cap, you'll notice a small ring label
on the exact center of the primary mirror. This "center mark"
allows you to achieve a very precise alignment of the primary
mirror; you don't have to guess where the center of the mirror is.
You simply adjust the primary mirror position (described below)
until the reflection of the hole in the collimating cap is centered
inside the ring.
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 centered in the
focuser drawtube,. If it isn't, as in Figure 9b, it must be adjusted.
Typically, this adjustment will rarely, if ever, need to be done.
Note: When make adjustments to the secondary mirror position,
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 10). Turning the screw clock-
wise 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
10
secondary mirror is centered left-to-right in the focuser drawtube,
rotate the secondary mirror holder until the reflection of the pri-
mary mirror is as centered in the secondary 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 sec-
ondary mirror in that position.
To adjust the secondary mirror up-and-down in the focuser
drawtube, adjust the length of the two spider vanes perpendicu-
lar to the focuser. This is done by tightening the knurled thumb-
nuts that secure the vanes to the tube (Figure 11). Loosen one
thumbnut, then tighten the other until the secondary mirror is
centered in the drawtube.
Spider
vane
thumbnuts
Figure 11.
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 within
the secondary mirror.
If the entire primary mirror reflection is not visible in the second-
ary mirror, as in Figure 9c, 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 12. You will need a 2.5mm hex key to do this.
The goal is to center the primary mirror reflection in the second-
ary mirror, as in Figure 9d. Don't worry that the reflection of the
secondary mirror within the primary mirror reflection (the small-
est circle, with the collimation cap "dot" in the center) is off-cen-
ter. You will fix that in the next step.
Figure 10.
To center the
s e c o n d a r y
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 center the secondary mirror up-and-down in the
Alignment set screws (3)
Figure 12.
Adjust the tilt of the
secondary mirror
by loosening one of
the three alignment
set screws then
tightening the
other two.