Orion 9786 - Manual (Page 4)

4
divide the focal length of the telescope by the focal length of
the eyepiece:
Telescope Focal Length (mm)
= Magnification
Eyepiece Focal Length (mm)
For example, the 6" Newtonian Imaging Reflector, which has
a focal length of 750mm, used in combination with a 25mm
eyepiece, yields a magnification of
750 mm
= 30x
25 mm
Every telescope has a useful limit of power of about 45x­60x
per inch of aperture. Claims of higher power by some tele­
scope manufacturers are a misleading advertising gimmick
and should be dismissed. Keep in mind that at higher pow­
ers, an image will always be dimmer and less sharp (this is
a fundamental law of optics). The steadiness of the air (the
“seeing”) will usually limit how much magnification an image
can tolerate.
Always start viewing with your lowest­power (longest focal
length) eyepiece in the telescope. After you have located and
observed the object with it, you can try switching to a higher­
power eyepiece to ferret out more detail, if atmospheric con­
ditions permit. If the image you see is not crisp and steady,
reduce the magnification by switching to a longer­focal­length
eyepiece. As a general rule, a small but well­resolved image
will show more detail and provide a more enjoyable view than
a dim and fuzzy, over­magnified image.
astroimaging with the 6" newtonian
imaging reflector
The 6" Newtonian Imaging Reflector has been specifically
designed for use with astronomical CCD imaging cameras
like the Orion StarShoot, but other imaging systems such as
digital SLR cameras will also work well with the telescope.
The secondary mirror of the 6" Newtonian Imaging Reflector
has been sized appropriately to provide a fully illuminated
field of view for Orion StarShoot cameras and most popular
digital SLR models.
Unlike most Newtonian reflector designs, the 6" Imaging
Reflector's secondary mirror has been recessed further into
the tube to prevent off­axis glare from being detected by imag­
ing devices. Glare can contaminate night­sky images by reduc­
ing image contrast and giving the object a “soft” appearance.
To use your CCD camera with the 6" Newtonian Imaging
Reflector, the camera must have a 1.25 inch “nosepiece”.
Otherwise an external camera adapter with T­threads is
required. All Orion StarShoot cameras feature this nosepiece
(Figure 2). Insert the nosepiece equipped camera into the
focuser just like an 1.25" eyepiece.
If your camera does not include a 1.25" nosepiece, you have
a digital SLR, or if you wish to utilize a secure T­thread con­
nection with a CCD camera like the Orion StarShoot, a zero­
profile camera adapter is required (available from Orion). The
zero­profile adapter is inserted into the focuser just like a 2"
eyepiece and provides T­threads for attachment of digital SLR
T­rings or T­threaded CCD cameras.
To attach a digital SLR to the telescope, remove any attached
lenses and connect a model­specific T­ring to the camera
body. Thread the T­ring onto the zero­profile adapter to com­
plete attachment. To securely attach a CCD imaging cam­
era like the Orion StarShoot via T­threads, remove the 1.25"
nosepiece and thread the CCD camera onto the zero­profile
camera adapter to complete attachment.
Due to its imaging­optimized design, no external extension
tubes are required to appropriately couple the telescope to an
imaging camera.
To record an image of a night­sky object, you will need to first
acquire and center the object with an eyepiece. You may need
to extend the focuser’s built­in extension tube to achieve focus
with an eyepiece. Once you have centered the target object
in the eyepiece field of view, remove the eyepiece and insert
your CCD camera into the telescope’s focuser (don’t forget
to retract the built­in extension tube if it has been extended).
Secure the camera with the thumbscrew on the focuser. Use
the focus and fine­focus wheels to bring the image into focus.
collimating the optics
Collimating is the process of adjusting the mirrors so they are
aligned with one another. Your telescope’s optics were aligned
at the factory, and should not need much adjustment unless
the telescope is handled roughly. Accurate mirror alignment is
important to ensure peak performance of your telescope, so it
should be checked regularly. Collimating is relatively easy to
do and can be done in daylight.
To check optical alignment, remove the eyepiece and look
down the focuser drawtube. You should see the secondary
mirror centered in the drawtube, as well as the reflection of
the primary mirror centered in the secondary mirror, and the
reflection of the secondary mirror (and your eye) centered in
the reflection of the primary mirror, as in Figure 3a. If anything
is off­center, proceed with the following collimating procedure.
The Collimating Cap and Primary Mirror Center Mark
Your 6" Newtonian Imaging Reflector comes with a collimat­
ing cap. This is a simple cap that fits on the focuser drawtube
like a dust cap, but has a hole in the center and a silver bot­
Figure 2. To use a CCD camera with the 6" Imaging OTA, the
camera must have a 1.25” nosepiece, like the Orion StarShoot
Imaging cameras, or else an external camera adapter with
T­threads is required.
1.25" nosepiece