Instruction manual

22
PROPER CARE FOR YOUR TELESCOPE
C
ollimating a Newtonian reflector
Fig.j
Correctly aligned
Primary mirror
Support for
secondary mirror
Secondary mirror
Focuser
Needs collimation
Primary mirror clip
Ignore the reflected
image for now
Primary mirror clip
Primary mirror clip
Primary mirror clip
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.j).
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.j-1).
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.j-2)
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.j-3), 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
Fig.j-1
Fig.j-2
Fig.j-3
Fig.j-4