Bresser National Geographic Bedienungsanleitung Seite 20

Telescope ABC's
What do the following terms mean?
Erecting lens (18):
The erecting lens is set into the eyepiece holder of the telescope before the eyepiece itself. This lens
can produce an additional magnifi cation (mostly around 1.5 X) via the integrated lens in the eyepiece.
The image will be turned around if you use an erecting lens, but it appears upright and even properly
oriented on the vertical axis.
Eyepiece (15):
An eyepiece is a system made for your eye and comprised of one or more lenses. In an eyepiece, the
clear image that is generated in the focal point of a lens is captured and magnifi ed even more.
There is a simple formula for calculating the magnifi cation:
Focal width of the telescope tube / Focal width of the eyepiece = Magnifi cation
In a telescope, the magnifi cation depends on both the focal width of the telescope tube and the focal
width of the eyepiece.
From this formula, we see that if you use an eyepiece with a focal width of 20 mm and a telescope tube
with a focal width of 600 mm, you will get the following magnifi cation:
600 mm / 20 mm = 30 times magnifi cation
Focal width:
Everything that magnifi es an object via an optic (lens) has a certain focal width. The focal width is the
length of the path the light travels from the surface of the lens to its focal point. The focal point is also
referred to as the focus. In focus, the image is clear. In the case of a telescope, the focal widths of the
telescope tube and the eyepieces are combined.
Lens:
The lens turns the light which falls on it around so that the light gives a clear image in the focal point after
it has traveled a certain distance (focal width).
Magnifi cation:
The magnifi cation corresponds to the difference between observation with the naked eye and observa-
tion through a magnifi cation apparatus (e.g. a telescope). In this scheme, observation with the eye is
considered 'single', or 1 X magnifi cation. Accordingly, if a telescope has a magnifi cation of 30 X, then
an object viewed through the telescope will appear 30 times larger than it would with the naked eye.
See also 'Eyepiece'.
Zenith mirror (16):
A mirror that defl ects rays of light at a 90 degree angle. With a horizontal telescope tube, this device
defl ects the light upwards so that you can comfortably observe by looking downwards into the eyepiece.
The image in a zenith mirror appears upright, but rotated around its vertical axis (what is left appears
right and vice versa).
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