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The eyepiece, is the optical element that magnifies the image focused by the telescope. The eyepiece fits directly into the
star diagonal. To install the eyepiece:
1.
Loosen the thumbscrew on the star diagonal so it does not obstruct the inner
diameter of the eyepiece end of the diagonal. Remove the protective dust cap
from the star diagonal's barrel.
2.
Slide the chrome portion of the low power 25mm eyepiece into the star
diagonal.
3.
Tighten the thumbscrew to hold the eyepiece in place.
To remove the eyepiece, loosen the thumbscrew on the star diagonal and slide the
eyepiece out.
Eyepieces are commonly referred to by focal length and barrel diameter. The
focal length of each eyepiece is printed on the eyepiece barrel. The longer the
focal length (i.e., the larger the number) the lower the eyepiece power or
magnification; and the shorter the focal length (i.e., the smaller the number) the
higher the magnification. Generally, you will use low-to-moderate power when viewing. For more information on how to
determine power, see the section on "Calculating Magnification."
Barrel diameter is the diameter of the barrel that slides into the star diagonal or focuser. The NexStar uses eyepieces with
a standard 1-1/4" barrel diameter.
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The NexStar's focusing mechanism controls the primary mirror which is mounted on a ring that slides back and forth on
the primary baffle tube. The focusing knob, which moves the primary mirror, is on the rear cell of the telescope just below
the star diagonal and eyepiece. Turn the focusing knob until the image is sharp. If the knob will not turn, it has reached
the end of its travel on the focusing mechanism. Turn the knob in the opposite direction until the image is sharp. Once an
image is in focus, turn the knob clockwise to focus on a closer object and counterclockwise for a more distant object. A
single turn of the focusing knob moves the primary mirror only slightly. Therefore, it will take many turns (about 25) to
go from close focus (approximately 20 feet) to infinity.
For astronomical viewing, out of focus star images are very diffuse, making them difficult to see. If you turn the focus
knob too quickly, you can go right through focus without seeing the image. To avoid this problem, your first astronomical
target should be a bright object (like the Moon or a planet) so that the image is visible even when out of focus. Critical
focusing is best accomplished when the focusing knob is turned in such a manner that the mirror moves against the pull of
gravity. In doing so, any mirror shift is minimized. For astronomical observing, both visually and photographically, this
is done by turning the focus knob counterclockwise.
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The Star Pointer is the quickest and easiest way to point your telescope exactly at a desired object in the sky. It's like
having a laser pointer that you can shine directly onto the night sky. The Star Pointer is a zero magnification pointing tool
that uses a coated glass window to superimpose the image of a small red dot onto the night sky. While keeping both eyes
open when looking through the Star Pointer, simply move your telescope until the red dot, seen through the Star Pointer,
merges with the object as seen with your unaided eye. The red dot is produced by a light-emitting diode (LED); it is not a
laser beam and will not damage the glass window or your eye. The Star Pointer comes equipped with a variable brightness
control, two axes alignment control and mounting brackets. Before the Star Pointer is ready to be used, it must be attached
to the telescope tube and properly aligned:
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Eyepiece
Diagonal
Visual accessories for the NexStar 90 & 127 MAK
8
Star Pointer
Finderscope
Star
Focuser Knob
Figure 2-6
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