Sky-Watcher DOB10 - Manual (Page 10)

C
ollimation
Fig.g
Fig.k
Correctly aligned
Fig.h
Primary mirror
Support for
secondary mirror
Secondary mirror
Focuser
Needs collimation
Fig.j
Primary mirror clip
Ignore the reflected
image for now
Primary mirror clip Primary mirror clip
Primary mirror clip
PROPER CARE FOR YOUR TELESCOPE
Fig.i
Adjusting screw
Primary
mirror
Mirror cell
Locking screw
10
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.g).
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.h).
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.i)
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), 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 loosen one and then
compensate for the slack by tightening the other two.
Stop when you see all three mirror clips (Fig.k). Make
sure that all three small alignment screws are tightened
to secure the secondary mirror in place.