INSTRUMENTS
ASTRAL TELESCOPE
The astral refractor telescope gives a good vision
of the planets and the moon. It can be quite long and do not have reversing
image system. The objective must be well corrected for the chromatism
aberration, it must be achromatic
or and with apochromatic, with or
without fluorite lenses. and also for the oculars. They can be used for
terrestrial observation but they have to have an erecting system attachment
made by lenses
or prisms. The tripod must be equatorial,
with pointing device to point to the polar star in order to align the telescope
to the terrestrial axe of rotation. Which is of most importance for a good
astral observation. The cheaper instrument for initiation have an azimuthal
tripod
| EQUATORIAL : The equatorial tripod have three axes. One is on the
terrestrial axe of rotation , which should be pointing to the polar star. On axe
equatorial and perpendicular axe . This type of fixation give the possibility to turn only
one axe to follow the stars, and axe can be motorized for the astro-photo and more
convenient observation. |
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AZIMUTHAL : The azimuthal tripod permits movement in two axes,
horizontal and vertical, which means that we must turn both axes in order to follow the
stars. These tripods are made for a terrestrial observation. |
What
happens with heat and UV radiation:
In
looking through binoculars, there is absolutely no danger for the user from UV
radiation. On account of the thickness of the optical lenses, especially of the
prisms, short-wave light (UV light) is fully absorbed. Available effect
coatings, as for example red coatings, bring about only an unnecessary reduction
of transmission
"High
Definition":
HD
telescopes include at least one lens with extremely low dispersion. The
advantage is an increase of contrast and resolution and a significant reduction
of color fringes. (Dispersion means the separation of colors in the refraction
of white light.)
ACHROMATIC: Lenses that are corrected for two light waves for
chromatic faults. This means that the coloured fringe on the border of objects can be
eradicated, providing better image quality.
APOCHROMATISM :This is the same
as achromatic except for three light waves which provide a far better image.
FLUORITE :An additive for glass
in order to obtain a better image.
ERECTING SYSTEM : The erecting
system allows the image to be flipped from left to right and top to bottom.
PRISM : Prisms are optical
elements for reflecting the image (mirror effect) and then flipping it. The PORRO prism
flips the image in two steps and in pairs. The roof prism flips the image from top to
bottom and left to right in one piece of glass. This diminishes loss of light and gives a
more compact instrument.
ERECTING LENS: Erecting
lenses are optical systems made with negative lenses to flip the image.
Choosing a spotting
scope
There are
several factors to
consider when choosing
a sporting scope.
Listed below are
the more important
criteria that you
may wish to
consider.
DIAMETER OF OBJECTIVE
LENS
A spotting
scope is really
a telescope that
produces an upright
image. The major
function of a
spotting scope, like
ail telescopes, is
to gather incoming
light. The larger
the diameter of
the spotting scope's
objective lens, the
more light it
gathers, with more
light translating into
a brighter and
better image. As
the size of
the objective lens
increases, greater detail
and clarity of
image will be
afforded.
MAGNIFICATION (POWER)
Magnification is
the degree to
which the object
being viewed, is
enlarged.
Magnification, or power,
in a spotting
scope is a
function of the
relationship of two
independent optical systems
-- the optics
of the spotting
scope itself and
the eyepiece being
used. To determine
magnification, divide the
focal length of
the spotting scope
by the focal
length of the
eyepiece.
By exchanging an
eyepiece of one
focal length for
another eyepiece with
a different focal
length, you can
increase or decrease
the magnification of
the spotting scope.
For example, a
30mm eyepiece used
on a C90
spotting scope with
a 1000mm focal
length would yield
a magnification of
33x. A 9mm
eyepiece used on
the same C90
spotting scope would
yield a power
of ll0x.
There is, however,
a limit to
how much you
can magnify an
image. As a
rule of thumb,
the maximum magnification
is equal to
50 to 60
times the diameter
(in inches) of
the spotting scope's
objective lens (under
ideal conditions). Magnification
higher than this
will produce a
dim and fuzzy
image. In most
cases, a magnification
of 20 to
35x is the
most useful and
satisfying range to
use with spotting
scopes under normal
daytime conditions. Zoom
spotting scopes have
a single, built-in
eyepiece to give
you a range
of magnifications without
the need to
change eyepieces.
FOCAL LENGTH
The distance, in
an optical system,
from the objective
lens to the
point where the
instrument is in
focus (the focal
point). The longer
the focal length
of the instrument,
the larger the
image scale it
offers. « NEAR
FOCUS The distance
between the instrument
and the nearest
object you can
focus on, while
maintaining a good
image and sharp
focus, defines the
near focus. Short
near focus is
important for close-up
visual and photographic
work.
FIELD OF
VIEW
The size of
the area, in
degrees, that can
be seen while
looking through the
spotting scope is
the angular field
of view. Linear
field of view
refers to the
width of the
area that can
be observed at
1,000 yards, and
is expressed in
feet.
A larger field
of view translates
to a larger
area seen through
the spotting scope.
Field of view
is related to
magnification, with greater
magnification creating
a smaller field
of view, in
general. The angular
field of view
is calculated by
dividing the apparent
field of the
eyepiece by the
magnification being used.
(AFE + Magnification
= AFV). Once
the angular field
of view is
known, the linear
field can be
determined by multiplying
the angular field
by 52.5.
FOCAL RATIO OR
PHOTOGRAPHIC SPEED (F/STOP)
The ratio
of the focal
length of the
spotting scope to
the diameter (aperture)
of its objective
lens, in millimeters.
Spotting scopes with
small f/stop numbers
react to incoming
light faster than
spotting scopes with
larger f/stop numbers.
So, the smaller
the f/stop number,
the shorter your
photographic exposure time.
Twilight
factor:
This
number (multiplying the magnification with the objective lens diameter and then
taking the square root) gives you limited mathematical information about the
performance of the instrument under twilight conditions and does not say
anything about the optical design or the lens coatings that influence light
transmission. For instance, a telescope with a 60-times magnification or more
has a tremendous twilight factor - but is not useable at twilight for most
purposes because the exit pupil size decreases as magnification increases. In
general, quality binoculars with an exit pupil of at least 0.2 inch (5mm) are
good for hunting under twilight conditions.
EXIT PUPIL
The diameter, in
millimeters, of the
beam of light
that leaves the
eyepiece of the
spotting scope is
the "exit pupil'.
To calculate the
exit pupil, divide
the size of
the objective lens,
in millimeters, by
the magnification of
the eyepiece being
used. The larger
the exit pupil,
the brighter the
image.
EYE RELIEF
The minimum
distance between the
eyepiece of the
spotting scope and
your eye that
still allows you
to see the
entire field of
view.
COATINGS
Optical coatings are
important, as they
determine the throughput
transmission of a
spotting scope. The
better the quality
of the lens
coatings, the brighter
the image will
be and the
higher the contrast
of the image
will be. Fully
multicoated lenses are
the best quality
you can choose.
PORTABILITY
For applications
such as hiking
and hunting, portability
is a prime
factor to consider.
For stationary viewing,
a large diameter
objective lens becomes
of primary importance.
VERSATILITY
Most Celestron
spotting scopes can
be used three
different ways: (1.
As a telephoto
lens when attached
to a 35mm
SLR camera, (2).
;or terrestrial observing,
and (3). As
a telescope. This
is the kind
of versatility you
want.
CONSTRUCTION
Both mechanical
and optical construction
are important. Alignment
of the optical
elements (collimation)
is critical for
achieving optimal results.
All Celestron spotting
scopes are laser
aligned to ensure
comfortable viewing, even
during extended viewing
sessions.
Using a spotting scope as a telephoto lens
A long
telephoto lens brings
you close optically
when you can't
get close physically. Distance shrinks
between you and
your subject, allowing
you to capture
both far away
and close-up images
on film.
Most Celestron spotting
scopes are designed
to be dual
purpose visual and
photographic instruments.
For photographic use,
all that's required
is a T-
Adapter for the
spotting scope and
the correct T-ring
for your particular
35mm SLR camera.
With these two
simple, inexpensive accessories
the usability of
your spotting scope
is easily enhanced.
The criteria given
to consider in
choosing a spotting
scope applies equally
well when choosing
a telephoto lens.
The following pictures
demonstrate what a
telephoto lens can
do. The picture
on the top
is a standard
50mm photo and
the picture on
the bottom was
taken with Celestron's
C90 spotting scope
(l000mm) at the
same distance.
A few exemples:
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Refracting telescope- ø90mm- f.1000 1757
ACCESSORIES SUPPLIED WITH INSTRUMENT: multi-coated optics of ø114 f. 910, f/8, two ø 31.8 eyepieces, K9
(100X), K25 (36x). Equatorial mount with motor on both axes with two section aluminium
tripod (from 77 cm. to 132 cm.). 6 x 30 finder with achromatic lenses, rack and pinion
focus, micrometric regulation of latitude, polar scope, instructions for use.
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Nextar 60 GT
the easily assembled, quick-release, most user-friendly telescope available today. All NexStar HC series telescopes come with a directional hand control manual high-speed slewing and fine gentel at a touch of a button. Plug the directional hand control into your laptop or PC and control the NexStar with the included "GuideStar" PC software, capable of automatically swelling thousands of night-time objects. Or if you want all the power of the GuideSfar software in palm of your hand, the NexStar 5T series telescopes come with a completely computerized hand control with an illuminated numeric key pad and dual 16 character LCD display. Simply tell the hand control the date, location and position of north and the NexStar virtually aligns itself, then selects and goes to the best objects in the sky. |
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Nextar 80 GT
Our most affordable NexStar telescopes turn starry nights into space odysseys. These 80mm refractors come with either a directional hand control HC models or fully computerized hand control [GT models], with a database of over 4,000 celestial objects. It includes three Ø 1¼, eyepieces for magnifications of 35x. 70x and 175x as well as The Sky Level 1 cd-rom software. With the pre-assembled, adjustable aluminum tripod the NexStar GT can be up and ready to use in a matter of minute . |
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Refracting telescope- ø60mm- f.900 1739
ACCESSORIES SUPPLIED WITH INSTRUMENT: Optics ø60, f.900, f/15, two eyepieces ø24.5mm. H20mm(45x) and H8mm(112x), 90¡ astronomical
prism. Equatorial mount, two section wooden tripod, 5x24 finder, 2x Barlow lens, 1.5x
erecting lens, instructions for use.
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Refracting telescope- ø60mm- f.700 1735
ACCESSORIES SUPPLIED WITH INSTRUMENT: Optics ø60, f. 700, f/11.6, two eyepieces ø24.5mm. H20mm(35x) and H8mm (87x), 90¡ astronomical
prism. Azimuthal mount, two section wooden tripod, 5 x 24 finder, 2x Barlow lens, 1.5
erecting lens, instructions for use.
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CELESTRON C 6 R GOTO
For a completely
automated GoTo system, the C6-RGT {#21020) comes mounted on the CG-5
computerized EQ mount and allows access to feature, star alignment capability
and GoTo slewing to over 40,000 object Equipped with high-speed motors and hand
control, the C6-RGT allows you to remotely slew your telescope to desired
objects quickly and accurately no matter at what level you are starting out, the
Advanced GT series will unfold all the universe for you and your friends.
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1-1/4" 20mm Eyepiece (60x)
9x50 Finderscope and Mounting Bracket
CG-5 Equatorial Mount and Tripod
Star Diagonal - Ø 11/4 "
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The Sky Level I CD-ROM
Accessory Tray
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40,000+ objects, 400 user defined
programmable objects
Enhanced information on over 200 objects
Double line. 16 character Liquid Crystal Display; Hand Control DC Servo Motors
with Encoders on both Axes
4°/second Max. Slew Speed
RS-232 communication port on hand control
Auxiliary Port and Autoguider Port on motor drive
General
Accessories (cont.)
Optical Accessories
Optical Accessories (cont.)
Orders Through
French
