7. Using the accessories, a bit of math
to understand how all it works.
Using the accessories is easy and fun. To
change magnification simply swap
eyepieces. To get more magnification
simply use the barlow lens. But how does
all of this work?
7.1. Power (magnification)
Your telescope has a focal length of
900mm. This is approximately the distance
between the telescope lens and its focal
point (very similar to the distance between
the focus point of a loupe and the loupe
lens). This is a very important feature, that
allows to determine several interesting
facts such as magnification.
The magnification is determined by the
telescope’s focal length and the used
eyepiece. You probably noticed that the
two supplied eyepieces are H20mm and
H12.5mm. This means that the H20mm is a
20mm focal length eyepiece while the
H12.5mm is a 12.5mm focal length
eyepiece.
To determine the magnification just divide
the telescope’s focal length by the
eyepiece’s focal length. Let’s give an
example for our telescope and the supplied
eyepieces:
Telescope’s focal length is 500mm.
H20 eyepiece’s focal length is 20mm.
900𝑚𝑚
20𝑚𝑚
= 45 𝑝𝑜𝑤𝑒𝑟
This means that the H20mm eyepiece
provides a 45x power (magnification). This
seems low, but when you try it, you will
see a bright image with some (very good)
details.
7.2. Barlow Lens
The barlow lens is a very interesting device.
It is a negative lens, that multiplies the
telescope’s focal length. So a 2x Barlow
multiplies the original focal length by 2x, in
this case 900𝑚𝑚 𝑥 2 = 1800𝑚𝑚.
A 3x Barlow lens multiplies by 3x.
Your telescope is supplied with a 2x Barlow
lens. When used with the H20mm eyepiece
you get 2x the power obtained before
45 𝑝𝑜𝑤𝑒𝑟 𝑋 2𝑥 𝐵𝑎𝑟𝑙𝑜𝑤 = 90 𝑝𝑜𝑤𝑒𝑟
7.3. Erecting lens (not included)
The erecting lens gets you an upright image
view with the telescope. It also adds some
power like the barlow lens. The Erecting
Lens provides an extra 1.5x power.
Some possible accessory combinations
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