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Bresser 90-65000 National Geographic Manual

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millimeters, and it is written on each eyepiece. In general, the larger the focal width of an eyepiece, the smaller the
magnifi cation.
There is a simple formula for calculating the magnifi cation:
Focal width of the telescope tube / Focal width of the eyepiece
= Magnifi cation
The magnifi cation is also depends on the focal width of the telescope tube. The telescope has a focal length of
500 mm.
From this formula, we see that if you use an eyepiece with a focal width of 20 mm, you will get the following mag-
nifi cation:
500 mm / 20 mm = 25X magnifi cation
The table below shows some common magnifi cations.
Telescope tube
focal width
Focal width of eyepiece Magnifi cation Magnifi cation with
2X Barlow lens
500 mm 20 mm 25X 50X
500 mm 6 mm 83X 167X
NOTES on cleaning
• Clean the eyepieces and lenses only with a soft, lint-free cloth, like a microfi bre cloth. Do not apply excess pres-
sure to the cloth to avoid scratching the lenses.
• To remove more stubborn dirt, moisten the cleaning cloth with an eyeglass-cleaning solution, and wipe the lenses
gently.
• Protect the device from dust and moisture. After use, particularly in high humidity, let the device acclimatize for a
short period of time, so that the residual moisture can dissipate before storing. Remove the dust cover and store
it in the included bag during use.
• To remove dust on the mirrors, use a fi ne brush or air blower (from your local camera shop or optician). Don’t
touch any mirror surface with your fi ngers — they may damage the coating.
DISPOSAL
• Dispose of the packaging materials properly, according to their type, such as paper or cardboard. Contact your
local waste- disposal service or environmental authority for information on the proper disposal.
• Please take the current legal regulations into account when disposing of your device. You can get more informa-
tion on the proper disposal from your local waste-disposal service or environmental authority.
Telescope ABC:
What do the following terms mean?
Barlow Lens:
The Barlow lens was named after its inventor, Peter Barlow, a British mathematician and physicist who lived from
1776–1862. The lens can be used to increase the focal width of a telescope. Depending on the type of lens, it is
possible to double or even to triple the focal width. As a result, the magnifi cation can also be increased. Also, see
Eyepiece.
… 8 …


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