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Knurled ring
a.
Figure 4. (a
) Insert the finder scope into the bracket, then
the thumbscrew lock.
piece, or if you wish to utilize the camera's T-threads without
a coma corrector, a zero-profile prime focus camera adapter
is required (available from Orion). The zero-profile adapter
has male T-threads that couple to the female T-threads of your
camera. Note that, depending on your CCD camera's speci-
fications, you may need to insert the 2" extension adapter in
front of the camera in order to achieve focus.
You may also need to add T-thread spacer rings between the
coma corrector and the CCD camera, to achieve the neces-
sary critical distance between the coma corrector's rear lens
element and the camera's imaging sensor. Consult the manu-
als for your camera and the coma corrector to determine the
spacing needed.
Observing with the 6" f/4 Newtonian Astrograph
The 6" f/4 Newtonian Astrograph is optimized for photographic
imaging, but it can also be used for visual observing of celes-
tial objects. (Because the field of view in a Newtonian reflector
is rotated from right-side-up, this type of telescope is not rec-
ommended for terrestrial observing.) For visual use, we rec-
ommend using high-quality eyepieces to take full advantage of
the instrument's excellent optical quality.
To achieve focus with most eyepieces for visual use, you will
need to install the included 2" extension adapter in the focuser,
then insert either a 2" or 1.25" eyepiece into the extension
adapter. (If using a 1.25" eyepiece, you will need to insert the
1.25" adapter into the 2" extension adapter.) If you use a coma
corrector that works for visual use (some work only for photog-
raphy), you may not need the extension adapter to reach focus
with your eyepiece(s).
Collimating the Optics
(Aligning the Mirrors)
Collimating is the process of adjusting the mirrors so they are
aligned with one another. Precise collimation of the optics is
especially critical for fast Newtonian optics such as in the f/4
astrograph. If the mirrors are even slightly misaligned, image
Thumbscrews
O-ring
Spring pin
(b)
Dovetail finder
scope base
b.
install the bracket foot into the dovetail finder scope base and secure it with
quality will suffer. Your telescope's optics were collimated at the
factory, but it doesn't take much to knock them slightly out of
alignment. So you should check the collimation before every
observing or imaging session, to make sure it is dead on. The
process of collimation is a relatively easy and can be done in
daylight or darkness.
To check collimation, remove the eyepiece and look down the
focuser drawtube, keeping your eye centered in the drawtube.
You should see a reflection of the primary mirror (i.e., the big
mirror at the bottom of the tube) and inside it a smaller reflec-
tion of the secondary mirror (i.e., the small diagonally oriented
mirror under the focuser). The reflected image of the primary
and secondary mirrors should be centered to one another, with
your eye at the very center of the view. If the reflections do not
look aligned, some adjustment will be needed, so you should
proceed with the collimation procedure.
We strongly recommend the use of a laser collimating tool
such as the Orion LaserMate Deluxe to aid in collimating the
optics. A laser collimator will ensure a more precise collimation
than you can achieve just by "eyeballing" it. With fast optics like
those of the 6" f/4, getting a very precise collimation is critical
for obtaining the sharpest, crispest images, so a laser collima-
tor is a worthwhile (and small) investment.
The Primary Mirror Center Mark
You'll notice that the primary mirror of the 6" f/4.0 Newtonian
Astrograph has a tiny ring (sticker) marking its center. This
"center mark" allows you to achieve a very precise collimation
of the primary mirror; you don't have to guess where the exact
center of the mirror is.
NOTE: The center ring sticker need not ever be removed from
the primary mirror. Because it lies directly in the shadow of the
secondary mirror, its presence in no way adversely affects the
optical performance of the telescope or the image quality. That
might seem counterintuitive, but it's true!
Preparing the Telescope for Collimation
Once you get the hang of collimating, you will be able to do it
quickly even in the dark. For now, it is best to collimate in day-
Thumbscrew
lock
5
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