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Camera tripods or altazimuth mounts are desireable for ter-
restrial (land) viewing because they allow simple vertical and
horizontal movement of the telescope. An equatorial mount is
desirable for astronomical viewing because it allows easy
tracking of celestial objects as the Earth rotates. Also, the set-
ting circles on the mount enable you to locate objects by their
celestial coordinates (right ascension and declination), which
can be found in many observing books and star atlases.
Focusing
Point the telescope so the front end is aimed in the general
direction of an object you wish to view. When you first look in
the eyepiece, the image you see may be fuzzy, or out of focus.
If so, gently turn the focus knob with your fingers until the
image becomes sharp. Go a little bit beyond sharp focus until
the image just starts to blur again, then reverse the rotation of
the knob, just to make sure you've hit the exact focus point.
You will have to readjust the focus when aiming at subjects of
varying distances, or after changing eyepieces.
If you have trouble focusing, rotate the focus knob counter-
clockwise as far as it will go. Now look through the eyepiece
while slowly rotating the focus knob clockwise. You should
soon see the point at which focus is reached.
Do You Wear Eyeglasses?
If you wear eyeglasses, you may be able to keep them on
while you observe, if your eyepieces have enough "eye relief"
to allow you to see the whole field of view. You can find out by
looking through the eyepiece first with your glasses on and
then with them off, and see if the glasses restrict the view to
only a portion of the full field. If they do, you can easily
observe with your glasses off by just refocusing the telescope
the needed amount.
If your eyes are astigmatic, images will probably appear the
best with glasses on. This is because a telescope's focuser
can accommodate for nearsightedness or farsightedness, but
not astigmatism. If you have to wear your glasses while
observing and cannot see the entire field of view, you may
want to purchase additional eyepieces that have longer eye
relief.
Aligning the Finder Scope
The Apex 90mm comes with a 6x20 correct-image finder
scope, while the Apex 102mm and 127mm both come with a
6x26 correct-image finder scope. (The first number indicates
magnification, and the second number indicates the aperture
in millimeters.) The finder scope makes it easier to locate the
subject you want to observe in the telescope, because the
finder scope has a much wider field of view. Unlike most find-
er scopes, images viewed in the correct-image finder scope
will appear oriented the same as the naked eye, which makes
finding objects even easier. The 45° correct-image diagonal
provides a naked eye orientation for images in the main tele-
scope, so the view in the finder scope and main telescope will
be oriented the same, which is a great convenience.
Before you use the finder scope, it must be precisely aligned
with the telescope so they both point to exactly the same
4
spot. Alignment is easiest to do in daylight, rather than at
night under the stars. First, insert the 25mm eyepiece into the
telescope's focuser. Then point the telescope at a discrete
object such as the top of a telephone pole or a street sign that
is at least a quarter-mile away. Position the telescope so the
target object appears in the very center of the field of view
when you look into the eyepiece.
Now look through the finder scope. Is the object centered on
the finder scope's crosshairs? If not, hopefully it will be visible
somewhere in the field of view, so only fine adjustment of the
finder scope bracket's alignment thumb screws will be need-
ed. Otherwise you'll have to make coarser adjustments to
the alignment thumb screws to redirect the aim of the
finder scope.
Use the alignment thumb screws to center the object on the
crosshairs of the finder scope. Then look again into the tele-
scope's eyepiece and see if it is still centered there too. If it
isn't, repeat the entire process, making sure not to move the
telescope while adjusting the alignment of the finder scope.
Finder scopes can come out of alignment during transport of
the telescope, so check its alignment before each observing
session.
If, when looking through the finder scope, you notice that the
image is fuzzy, you will need to focus the finder scope for your
eyes. For the 6x20 finder scope of the Apex 90mm this is
done by rotating the finder's eyepiece. For the 6x26 finder of
the Apex 102mm and 127mm, this is done by first loosening
the lock ring that is located behind the finder's objective lens
cell (see Figure 5). Once the lock ring is loosened, thread the
objective lens cell in or out until the image appears sharp.
Then, retighten the lock ring behind the lens cell. The finder
scope is now focused, and should not need focusing again for
your eyes.
Calculating Magnification (Power)
To calculate the magnification, or power, of a telescope with
an eyepiece, simply divide the focal length of the telescope by
the focal length of the eyepiece:
Magnification = telescope focal length ÷ eyepiece focal
For example, the Apex 102mm, which has a focal length of
1300mm, used in combination with the supplied 25mm eye-
piece, yields a power of:
1300 ÷ 25 = 52x.
It is desirable to have a range of eyepieces of different focal
lengths to allow viewing over a range of magnifications. It is
not uncommon for an observer to own five or more eyepieces.
Orion offers many different eyepieces of varying focal lengths,
so check the catalog or website for a wide selection of addi-
tional eyepieces to choose from.
Every telescope has a useful limit of power of about 2x per
millimeter of aperture (i.e. 204 x for the Apex 102mm). Claims
of higher power by some telescope manufacturers are a mis-
leading advertising gimmick and should be dismissed. Keep
in mind that at higher powers, an image will always be dimmer
length
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