6
5. 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?
5.1. 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 PL25mm and
PL6.5mm. This means that the PL25mm is a
25mm focal length eyepiece while the
PL6.5mm is a 6.5mm 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 900mm.
PL25 eyepiece’s focal length is 25mm.
900
25
= 36
This means that the PL25 eyepiece provides a
36x power (magnification). This seems low,
but when you try it, you will see a bright
image with some (very good) details.
5.2. 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
900
2 = 1800
.
A 3x Barlow lens multiplies by 3x.
Your telescope is supplied with a 2x Barlow
lens. When used with the PL25mm eyepiece
you get 2x the power obtained before
36
2
= 72
5.3. 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 supplied
Erecting Lens provides an extra 1.5x power.
5.4. Diagonal Mirror (does not apply to this
model)
This diverts the light coming from the
telescope to an angle of 45 or 90 degrees. It is
useful because it provides a more confortable
position when observing.
Here are some examples on how to use the
accessories.
Some possible accessory combinations
Terrestrial
View
Moon
Deep Sky
Jupiter and
Saturn
Barlow Lens 2x
PL25mm Eyepiece
Yes
Yes
PL6.5mm Eyepiece
Yes
Yes
Power
Does not apply
139x
36x
72x
