Sky-Watcher AZ3 MOUNT - Manual (Page 14)

C
ollimating a Newtonian
PROPER CARE FOR YOUR TELESCOPE
14
Fig.n
Fig.r
Correctly aligned
Fig.o
Primary mirror
Support for
secondary mirror
Secondary mirror
Focuser
Needs collimation
Fig.q
Primary mirror clip
Ignore the reflected
image for now
Primary mirror clip Primary mirror clip
Primary mirror clip
Fig.p
Adjusting screw
Primary
mirror
Mirror cell
Locking screw
Collimation is the process of aligning the mirrors of your
telescope so that they work in concert with each other to
deliver properly focused light to your eyepiece. By
observing out-of-focus star images, you can test whether
your telescope's optics are aligned. Place a star in the
centre of the field of view and move the focuser so that the
image is slightly out of focus. If the seeing conditions are
good, you will see a central circle of light (the Airy disc)
surrounded by a number of diffraction rings. If the rings are
symmetrical about the Airy disc, the telescope's optics are
correctly collimated (Fig.n).
If you do not have a collimating tool, we suggest that you
make a "collimating cap" out of a plastic 35mm film
canister (black with gray lid). Drill or punch a small pinhole
in the exact center of the lid and cut off the bottom of the
canister. This device will keep your eye centered of the
focuser tube. Insert the collimating cap into the focuser in
place of a regular eyepiece.
Collimation is a painless process and works like this:
Pull off the lens cap which covers the front of the telescope
and look down the optical tube. At the bottom you will see
the primary mirror held in place by three clips 120º apart,
and at the top the small oval secondary mirror held in a
support and tilted 45º toward the focuser outside the tube
wall (Fig.o).
The secondary mirror is aligned by adjusting the three
smaller screws surrounding the central bolt. The primary
mirror is adjusted by the three adjusting screws at the back
of your scope. The three locking screws beside them serve
to hold the mirror in place after collimation. (Fig.p)
Aligning the Secondary Mirror
Point the telescope at a lit wall and insert the collimating
cap into the focuser in place of a regular eyepiece. Look
into the focuser through your collimating cap. You may
have to twist the focus knob a few turns until the reflected
image of the focuser is out of your view. Note: keep your
eye against the back of the focus tube if collimating
without a collimating cap. Ignore the reflected image of
the collimating cap or your eye for now, instead look for
the three clips holding the primary mirror in place. If you
can't see them (Fig.q), it means that you will have to adjust
the three bolts on the top of the secondary mirror holder,
with possibly an Allen wrench or Phillip's screwdriver. You
will have to alternately or loosen one and then
compensate for the slack by tightening the other two. Stop
when you see all three mirror clips (Fig.r). Make sure that all
three small alignment screws are tightened to secure the
secondary mirror in place.