Sky-Watcher EQ2 MOUNT - Manual (Page 22)

C
ollimating a Newtonian
PROPER CARE FOR YOUR TELESCOPE
22
Fig.r
Fig.v
Correctly aligned
Fig.s
Primary mirror
Support for
secondary mirror
Secondary mirror
Focuser
Needs collimation
Fig.u
Primary mirror clip
Ignore the reflected
image for now
Primary mirror clip Primary mirror clip
Primary mirror clip
Fig.t
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.r).
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.s).
The secondary mirror is aligned by adjusting the central bolt
behind it, (which moves the mirror up and down the tube), and
the three smaller screws surrounding the bolt, (which adjust the
angle of the mirror). 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.t)
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.u), 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.v). Make sure that all three small
alignment screws are tightened to secure the secondary
mirror in place.