Orion 23013 Instruction Manual page 7

Figure 4A. The view down the focuser tube of a Newtonian
reflector with eyepiece removed. In this example, the optical
system is badly out of collimation.
use a collimation tool
To aid in centering your line of sight down the focuser drawtube,
and in centering the mirror reflections during collimation, it is very
helpful to use a precision collimating tool containing crosshairs,
such as the Orion Collimating Eyepiece #3640. We highly recom-
mend that you purchase one, as you will use it for as long as you
own this, or any, reflecting telescope.
Mechanically centering the Mirrors in the
optical tube
With the telescope pointed away from the Sun, stand a couple
feet away from the front of the telescope and look down the opti-
cal tube. Check that the secondary (or diagonal) mirror is
positioned in the center of the tube. Use a ruler if necessary to
measure the distance from the center of the secondary mirror
holder to the inside of the tube along each of the four "spider"
vanes; the distance should be roughly the same along each vane.
The spider adjustment is set at the factory, so it will probably be
fine right out of the box.
Should you have to adjust the secondary mirror position, do so
by turning the socket-head screws on the ends of the spider
vanes; the screw heads are located on the outside of the optical
tube (refer to Figure 3). You will need the small Allen wrench
(provided) for this. Unthread one bolt a small increment while
threading in the opposite bolt the same increment. Work with two
bolts at a time until the mirror is centered.
Now check that the primary mirror is roughly centered in the opti-
cal tube. There should be an equal amount of space between the
edge of the primary mirror and the inside of the optical tube all
the way around. A quick visual inspection usually suffices. If the
Figure 4C. Secondary
mirror correctly aligned
(tilted).
primary is obviously not centered, it will need to be repositioned
in its mirror cell.
centering the secondary Mirror under the
Focuser
Next, if there is an eyepiece in the telescope, remove it. Look down
into the open focuser drawtube at the secondary (diagonal) mirror.
It should be centered in the field of view. You will see the secondary
mirror and mirror holder as well as reflections of the secondary
mirror and holder and the primary mirror, and your eye. It's pretty
confusing, so refer to Figure 4A to sort them all out. (This figure
shows what you would see if both the primary and secondary mir-
rors were out of alignment and the secondary mirror were not
centered below the focuser tube.)
If the secondary mirror is not in the center of the focuser drawtube,
it must be adjusted. It helps to put a piece of white paper on the
inside of the optical tube opposite the focuser. The white paper
forms a bright background behind the secondary mirror as you
look down the focuser drawtube, making it easier to distinguish
the mirror holder from the background.
The secondary mirror is moved forward and back on a threaded rod
that extends from the secondary mirror into the four-vane spider
center support. The threaded rod has nuts on both sides of the
spider to hold it in place (see Figure 3). By threading the two nuts
in one direction or the other, you can move the rod forward or back
to correctly center the secondary mirror under the focuser. When
you've achieved the correct position (Figure 4B), make sure the two
nuts are threaded against the spider center support to hold the rod
securely in place.
Figure 4B. Secondary mirror
centered under focuser
tube, viewed through the
collimating Eyepiece (as are
the next two illustrations).
Figure 4D. Primary mirror
correctly aligned. The
telescope's optical system
is now collimated.
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