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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 magnification can also be increased. Also, see Eyepiece.
Focal width:
Everything that magnifies 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 bends the light which falls on it in such a way that the light creates a clear image at the focal point, after it has
traveled a certain distance (focal width).
Eyepiece:
An eyepiece is a viewing system comprised of one or more lenses. The eyepiece magnifies the clear image generated
at the focal point of a lens.
There is a simple formula for calculating magnification:
Focal width of the telescope tube / Focal width of the eyepiece
= Magnification
In a telescope, the magnification depends on both the focal width of the telescope tube and the focal width of the
eyepiece.
Magnification:
The magnification corresponds to the difference between observation with the naked eye and observation through a
magnification apparatus (e.g. a telescope). Observation with the naked eye is considered single, or 1x magnification.
Accordingly, if a telescope has a magnification of 30X, then an object viewed through the telescope will appear 30 times
larger than it would with the naked eye. Also see Eyepiece.
Useful accessories can be found at www.bresser.de
Possible objects for observation:
We have compiled and explained a number of very interesting celestial bodies and star clusters for you. On the accom
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panying images at the end of the instruction manual, you can see how objects will appear in good viewing conditions
through your telescope using the eyepieces that came with it.
The Moon
The moon is the Earth’s only natural satellite.
Diameter: 3,476 km
Distance: approx. 384,400 km from Earth
The moon has been known to humans since prehistoric times. It is the second brightest object in the sky (after the sun).
Because the moon circles the Earth once per month, the angle between the Earth, the moon and the sun is constantly
changing; one sees this change in the phases of the moon. The time between two consecutive new moon phases is
about 29.5 days (709 hours).
