Manual Bresser 90-11100 National Geographic (page 20 of 52) (English, German, Dutch, French, Italian, Spanish)

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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.

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Bresser 90-11100 National Geographic Manual

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