16
Instruction manual
Starscopes on azimuthal mount
Theoretically, almost any magnification is
possible with a telescope if you use the right
eyepieces. As you can see in the table above,
in the example with the 4 mm eyepiece and a
2x Barlow lens even a magnification of 350x
can be achieved. With even smaller eyepiece
focal lengths and stronger Barlow lenses (e.g.
3x, 5x) this could be increased almost arbitra-
rily. However, the useful magnification range
is limited by the laws of optics.
For the highest useful magnification, the rule
of thumb is that you should choose a maxi-
mum magnification of twice the diameter of
the optics.
For example, if the telescope has an diameter
of 76 mm, the highest magnification should
the highest magnification should not be more
than 76 x 2 = 152x. If you go beyond this
range, the image will become dark and the
sharpness will decrease, so you will see less
detail despite the higher magnification.
Magnification is also often limited by what is
called „seeing“ (air turbulence in the Earth’s
atmosphere).
Depending on the night of observation, the air
may be calmer or less calm. The highest use-
ful magnification can only be achieved when
the air is as calm as possible.
The lowest useful magnification is limited by
the so-called exit pupil (EP). The exit pupil is
the diameter of the light beam that is directed
from the eyepiece into your eye.
Here’s how to calculate the exit pupil:
Aperture of the telescope / Magnification
= diameter of theexit pupil
If the exit pupil is larger than the pupil of your
eye, light is lost and the image becomes dar-
ker. It is believed that the human pupil dilates
to a maximum diameter of 5-7 mm in comple-
te darkness. Therefore, avoid magnifications
that result in an exit pupil that is too large.
Examples (aperture of the telescope and
lowest reaonable magnification):
60 mm
8,5–12x
70 mm
10–14x
76 mm
11–15x
Highest and lowest useful magnification
Observing with the telescope
1. Always set up the telescope outdoors. It is best to
place the telescope outdoors about 30 minutes before
observing so that the optics can adjust to the ambient
temperature. Observing from inside a building through
a window (whether open or closed) is not recommen-
ded, since the image quality deteriorates significantly
as a result of the air exchange.
2. choose a location for observation that is as dark as
possible. This is especially important if you want to
observe faint objects such as star clusters, gas ne-
bulae, or even galaxies. Spend some time in the dark
before observing to give your eyes a chance to adjust
to the dark. Avoid looking directly into bright light, as
this will undo the dark adaptation. Use a red light lamp
that is not too bright for orientation at night.
3. Remove the dust caps from the telescope before
observing. On some telescopes (e.g. 76/700 mm New-
tonian telescope) the cap is in two parts. Remove the
entire cap, not just the inner part.