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1 - What is the difference between a refracting telescope and a reflecting
telescope? |
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The difference lies in their optical construction. The refracting telescope
uses a system of lenses, while a reflecting telescope uses a system of
mirrors. |
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2 - What are the advantages of a refracting telescope? |
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A refracting telescope achieves its best in observing bodies that show high
emissions of light, such as planets or stars, as it gives more detailed
images and with a higher contrast, than a reflecting telescope. It may be
used for normal observations, too, as it could become a powerful spyglass,
with the purchase of an optional accessory called "image rectifier". |
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3 - What are the advantages of a reflecting telescope? |
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The capability to receive more light (as it’s usually greater in diameter)
makes the reflector ideal for observing objects with low light emissions,
such as nebulae and galaxies. The reflecting telescope has some advantages
in astronomical photography, too. |
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4 - What are the essential features of a telescope? |
Essentially, they are the lens diameter, the focal length and the mount:
-LENS DIAMETER (D): this is the most important element, as it influences the
telescopes’ capability to gather light and to give bright images. Doubling
lens’ diameter (in millimeters) we get the highest possible magnification.
-FOCAL LENGTH (F): this is the distance from the object to the focus. The
ratio between the focal length of the telescope and the focal length of the
eyepiece supplies the magnification.
-MOUNT: this is the support that joins the optical tube to the tripod.
Beginner telescopes have an altazimuthal mount that allows simple movements.
Medium level telescopes have an equatorial mount that allows you to follow
heavenly bodies during their movements across the sky. Professional
telescopes have got an equatorial mount with a polar spyglass, which is
useful to make easy astronomical photography. |
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5 - What can a telescope show? |
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The quality and quantity of objects we can observe depend mostly by lens
diameter and focal length, which determine the brightness of telescope, and
by the magnification power, too. Observing Saturn, for example, with about
an 80 magnification, the planet lies in a long field without details; with a
160 the planet shows surface details and its largest satellite, Titan; over
200 the planet shows many details, such as the shadow projected onto
planet's rings and few of its satellites. |
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6 - Which optional accessories are recommended for a telescope? |
The most useful accessory is the motor, which allows you to follow
automatically the heavenly bodies. This is indispensable when the telescope
is used for astronomical photography. Some telescopes are motorized in right
ascension only, while others are on both axes, right ascension and
declination.
For ideal performances we recommend to purchase supplementary eyepieces,
without exceeding a magnification equal to the double of telescope diameter
in millimeters.
Sometimes, another useful accessory can be the Barlow lens, that doubles the
magnification of each eyepiece (e.g. transforming a 80x eyepiece in a 160x).
Finally, an image rectifier, that allows a terrestrial use of the telescope,
is also recommended. |
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7 - Which models may be used for astronomical photography? |
Even a simple 60mm (2.4 inch) diameter model allows photography of the Moon
and other planets at low enlargement. With a 114mm (4.5 inch) diameter, it's
possible to photograph the most brilliant nebulae and galaxies.
A normal reflex camera is enough for this type of photography; it can be
connected to the telescope with a photo adapter plus a T-2 ring. If photos
require more than few seconds of exposition, it's necessary a motorized
mount, in order to prevent blurring. Each model of telescope with a diameter
superior to 114mm allows you to photograph a great quantity of heavenly
objects. |
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8 - Which are the ideal models for beginners? |
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For the newcomer to astronomy, the ideal choice is a 114 mm (4.5 inch)
diameter reflecting telescope or a 70 mm (2.8 inch) diameter refracting
telescope. These instruments provide the best ratio price/quality and allow
the observation of the majority of bright heavenly bodies. These models have
a mount that can be motorized, too. They are easy to use and affordable for
everyone. |
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