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Observation
Preparations Before Observation
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Refractive Telescopes like the FC-100DZ,
when under low temperatures may take
some time to stabilize. Taking the telescope
outside an hour before observing begins will
allow it to equalize with the colder air.
Visual Applications
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Determining Magnification
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The magnification of any eyepiece used with
the telescope can be calculated by using
the following formula:
(Focal Distance of the Telescope) / (Focal
Distance of the Eyepiece)
Example: Utilizing the LE-5mm
800mm / 5mm = 160x
Therefore, shorter focal length eyepieces
will produce high magnification. However,
generally the upper limit of magnification
will be 2x of the aperture (measured in
mm) of a telescope, and the lowest will be
0.14x of the aperture (measured in mm) of a
telescope.
With an aperture of 100mm, the FC-100DZ
upper limit becomes 200x and lower limit
becomes 14x, making the usable eyepiece
focus distance from 4 to 57mm. Takahashi
eyepieces, TOE-2.5mm, TOE-3.3mm, and
TAK-3.3UW mostly surpass this range,
so most are usable within this range on
a higher magnification. This telescope is
equipped with a high-performance objective
lens, as such if the conditions are good it
can still be used even if they surpass the
maximum magnification.
Diagonal Mirror & Diagonal Prism
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When observing objects near the zenith
is necessary, it is advisable to use a high
quality diagonal prism. The Takahashi 90-
degree prism diagonal is a quality multi-
coated prism and allows the observer to
easily view the zenith by looking down into
the prism. The diagonal prism has a 45-
degree light pass and produces an erect,
reversed (mirror) image. The diagonal prism
is designed to be used with 31.7mm(1¼”)
barrel eyepieces.
The prism’s light path length increases the
optical path length of the system. In order
to ensure proper focus, please connect
the prism to the telescope following the
appropriate system chart.
The 31.7mm(1¼”) diagonal prism is inserted
into the compression ring adapter at the
end of the focuser and is tightened until it
holds the diagonal prism firmly in place.
The eyepiece is then inserted into the
compression ring adapter of the diagonal
prism and held firmly in place by tightening
the compression ring.
The Takahashi 50.8mm(2") diagonal mirror
is useful for viewing with 50.8mm(2")
eyepieces. When used in conjunction
with the 50.8(2") to 31.7mm(1¼”) adapter,
31.7mm(1¼”) eyepieces can also be used.
Please refer to the appropriate system chart
for proper connections.
Astro Imaging
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Prime Focus Imaging
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When imaging with a telescope, focusing is
one of the most critical elements of making
great astro images. To achieve proper
focus, it is important to place the camera
sensor at the focal point of the telescope.
Because the focal length of the telescope
is large, it is also important to use a high
quality equatorial mount. Any unwanted
movement or error in tracking can ruin an
imaging session.
To produce images using the telescope,
one can use either a digital SLR, or a
