Orion STARBLAST 9814 - Manual (Page 10)

10
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 10b, 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 tele-
scope tube opposite the focuser (in other words, on the other
side of the secondary mirror) will also be helpful in collimating
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 secondary mirror holder sta-
tionary (be careful not to touch the surface of the secondary
mirror), while turning the center screw with a Phillips head
screwdriver (See Figure 11). 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.
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 10c; 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 12. The goal is to center the
primary mirror reflection in the secondary mirror, as in figure
10d. 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.
a.
b. c.
d.
e.
Figure 10. Collimating the optics. (a) When the mirrors
are properly aligned, the view down the focuser drawtube
should look like this. (b) With the collimation cap in place, if
the optics are out of alignment, the view might look
something like this. (c) Here, the secondary mirror is
centered under the focuser, but it needs to be adjusted
(tilted) so that the entire primary mirror is visible. (d) The
secondary mirror is correctly aligned, but the primary mirror
still needs adjustment. When the primary mirror is correctly
aligned, the “dot” will be centered, as in (e).
Figure 12.
Adjust the tilt of
the secondary
mirror by
loosening or
tightening the
three alignment
set screws with a
2mm hex key.
Alignment set screws (3)
Figure 11. 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.