23
PROPER CARE FOR YOUR TELESCOPE
C
ollimating a Newtonian reflector
Fig.s
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.s).
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.s1).
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.s2)
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.s3), 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.
Fig.s1
Fig.s2
Fig.s3
Fig.s4
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