INSTRUMENTS
ASTRAL TELESCOPE
page 14
ACCESSORIES
ACCESSORIES AND THEIR
USE:
Barlow's Lens This lens doubles the magnification of every telescope. The extremity of the
lesser diameter is placed in the lens holder (fig. 14) while the oculars are inserted in
the other part. One effect of the doubling of the degree of magnification is the notable
reduction of the field within the frame and in the brightness of the telescope.
Not all Barlow lenses are equal and there you will have to ask for one that is
specifically suitable for the type of telescope you are using.
Sun Filter:
The sun filter is one of the absolutely indispensable accessories to observe the sun with
telescope.
 |
The sun filter is screwed onto the oculars (if possible use in
conjunction with a solar prism) and observation must be carried out according to the
procedure laid down in the paragraph dealing with the sun. |
Solar prism
This is a prism that disperses a great part of the light and heat of the Sun by means of a
hole cut corresponding to its hypothenuse. It must be used in conjunction with a sun
filter applied to the ocular.
Mylar Sun Filter
(all apertures)
This is a special filter that is placed in front of the telescope in such a way as to
filter the light from the moment it comes from the sun. It is very safe and has an
aluminium stand and a Mylar membrane which is made to the highest standards of
reliability. Consult the mounting instructions for the telescope to see whether the
instrument in your possession can be used with a filter of this type.
Moon Filter
The brightness of the moon is very great, in particular when the moon is nearing its full
phase and a lot of details can be noted on its surface. In order to compensate for this
you will need to use a moon filter which can be screwed onto the ocular.
Nebula Filter
One of the greatest problems in observation is caused by light pollution, the effects of
which can be felt even at quite a distance from the city. Besides the "normal
atmospheric emissions", a great deal of light is present due to mercury or sodium
lamps. The Nebula filter with a wide band, blocks this type of emission, while allowing a
large part of the emission to pass through from the field of the visible spectrum coming
from the nebulae. This permits a more detailed view of nebulae and galaxies even where
light pollution is present. The filter should be screwed onto the ocular, in the same way
as a normal moon filter and can be used with an ocular of 31.8 mm.
KIT 4 coloured
filters
In the observation of the moon and planets, some details cannot be identified because of
the low color contrast. In this case the human eye tends to confuse the two colors
resulting in the eye making out a spot of one color only. Use of a colored filter allows
us to overcome this difficulty and therefore to see the planet in greater detail. For
oculars of 0 31.8 mm the code no. 1101 kit includes four colored filters: green-yellow,
yellow, orange and red, Yellow-green is very useful in increasing the contrast
between the blue and red details of Saturn and Jupiter. It gives good results on the seas
of Mars and on the Ring of Saturn.
Yellow is very useful in the observation of details of the moon, in
particular within aperture of 150mm. Good results are also obtained in increasing the
contrast between the blue details of Jupiter and Saturn. It highlights the contrast
between the red-orange and blue- green zones of Mars.
Orange : useful for the observation of Mars and to highlight, on Jupiter
and Saturn, the details of the bands and of the polar regions.
Red : on telescopes of Ø150 mm. it offers a result
similar to that of the orange filter. Besides this it offers a greater contrast, above all
for the blue-green details. It is useful in the observation of Mars, Saturn, Jupiter and
in bringing Mercury into relief during observation by day or at twilight. Warning! Be
careful not to aim the telescope at the Sun, which is very near to Mercury.
Automatic Tracking
(motors)
For photography observation, and also for prolonged observation, it
is necessary to use a motor in order to automize the long tracking of the Right Ascension
Axis. Only usable with equatorial mounting, which has the necessary characteristics for
mounting a motor.
There are two main versions: SYNCHRONE: a cheap motor which is very reliable (with no
command button). It is limited in that it can only function at a current of 220V and so
cannot be used far away from buildings.
This can be remedied by using a CONTROL 12 transformer described later on in this
booklet.
STEP MOTOR:
fed
by a 12V battery (regular or rechargeable) it allows greater freedom of movement. It costs
more than the synchrone motor but offers the possibility of using a command button or
shutter release.
Consult the instructions for mounting your telescope in order to see which motor you can
use. On professional models it is possible to motorize even the movement in Declination,
in order to make the whole photography process easier.
Control 12
This instrument resolves the problem of many amateur telescopes where
the automatic Right Ascension movement is permitted only by a synchrone motor fed by 220V
without a command button. This type of instrument has, of necessity, to be used near home
(as those who possess one well know), and therefore it is impossible to take the
instrument to a place where the level of light pollution is at a minimum.
With the CONTROL - 12, those who possess a 220V motor can do as follows:
1) feed the motor with a 12V battery, from among the car battery range (by means of a
cable that can be connected to the lighter) or by means of a normal rechargeable,
portable, 12V battery.
2) Use a command pulse button in order to correct any tracking errors.
3) regulate the focus by means of the command button (on particular models).
Sun Screen
This is a white screen, a ring and a rod. Insert the ocular in the
lens quarter and position the screen at the required distance in order to obtain the
desired projection of the sun's image onto the white screen without running any risk to
your eyes.
Image Rectification
(for terrestrial use):
This allows for the rectification of the image (normally seen in reverse in ail astronomy
telescopes) in order to facilitate terrestrial use of the telescope. The rectifier is
inserted in the lens carrier of the telescope (fig. 13) once the ocular has been removed
and inserted in the top part of the rectifier. Different types of rectifier exist.
1) with lenses: cheaper, and generally capable of multiplying by 1.5 times the
magnification given by the ocular. Found only in Ø24.5mm models.
2) Porro Prism: top quality with no increase in magnification.
3) with lenses and Porto Prism: for some Newtonian models this is the only possibility.
This type multiplies by 2.8 times the magnification of the ocular.
4) Amici Prisms: only in Ø31.8 mm models.
This is a cross between an image rectifier and a rectifying prism. It resembles an
astronomy prism (with an exit of 45 °) only that it completely rectifies the image.
Consult the mounting instructions to see which type of rectifier can be used with your
type of instrument.
Motorized focusing
In the majority of Newtonian telescopes of Ø114mm, and in the
greater part of refractors up to Ø60mm. it is possible to use this accessory which allows
you to regulate the focus using the command pulse button. It is extremely practical,
whether in the case of photography or in simple observation. It avoids the irritating
vibrations that can occur when we "touch" the instrument in order to regulate
the focus. Consult your instructions for mounting the instrument in order to see which
type of rectifier can be used with your particular instrument.
ADVICE
FOR SUCCESSFUL OBSERVATION
When you take the telescope outside, and the outdoor
temperature is cooler than that indoors, the optics mist over and it is necessary to wait
for about 20 minutes to allow the optics to adapt to the new temperature. If you should
accidentally touch the ocular lenses with your fingers, or with your eyelashes, clean the
lenses immediately using the tissue and the special liquid supplied for this purpose
(available at all shops selling photography accessories.) If the lenses are not clean, you
will merely see confused images. Before starting your observation at night, allow your
eyes to adapt to the darkness. After about half an hour you will be able to perceive
celestial objects even those of weaker strength and brightness.
MAINTENANCE OF THE
TELESCOPE
The telescope is an optic and mechanical instrument of precision and
it has to be handled with care. When not in use, it should be kept in its case. The lenses
and the mirrors should be cleaned and polished with care and require delicate treatment in
order to avoid damage. The dismantling of the telescope or the detaching of its various
parts should only be undertaken by experts. When it is necessary to clean the optics, a
delicate solution should be used (neutral soap and water for example.) Clean cloths should
be used in the cleaning and under no circontances should abrasives of any kind be used.
The parts should be left in the air to dry out. Drying should not be done with any type of
absorbent material. Avoid using solvents such as xylene or ethyl alcohol. The oculars too
should be used and cleaned with care. They are vulnerable to damage insofar as they are
made to be interchangeable and, as a result of their ease of handling, can fall easily and
so lose their important optic alignment, with disastrous results.
All mirror telescopes are accurately collimated in the factory before packaging and it is
unlikely that you will need to carry out this type of regulation before starting
observation. However, if the telescope has been subjected to a hard knock during transport
you will need to recollimate the mirror system. If the image is not clear, even at a low
level of magnification, it could be that the instrument is out of alignment. In this case
consult the service technicians in order to resolve the problem.
French