National Geographic 80-30124 Manual De Instrucciones página 8

Aperture
102mm
Magnification
The magnification corresponds to the difference between observation with the naked eye and observation
through a magnifying device like a telescope. If a telescope configuration has a magnification of 30x, then an
object viewed through the telescope will appear 30 times larger than it would with the naked eye. To calculate
the magnification of your telescope setup, divide the focal length of the telescope tube by the focal length of
the eyepiece. For example, a 20mm eyepiece in a telescope with a 1000mm focal length will result in 50x power,
which will make the object appear 50 times larger. If you change the eyepiece, the power goes up or down
accordingly.
Focal ratio
The focal ratio of a telescope is determined by dividing the telescope's focal length by its aperture (usually
expressed in millimeters). It plays a key role in determining a telescope's field of view and significantly impacts
imaging time in astrophotography. For example, a telescope with a focal length of 1000mm and a 100mm clear
aperture has a focal ratio of f/10.
Exit Pupil
The exit pupil is the diameter of the beam of light coming out of the eyepiece. To calculate exit pupil, divide the
focal length of your eyepiece by your telescope's focal ratio. For example, if you use a 20mm eyepiece with an f/5
telescope, the exit pupil would be 4mm.
Eye Relief
Eye relief is all about a comfortable viewing experience because it is the distance at which you need to position
your eye from the eyepiece's outermost surface to enjoy the full field of view. This characteristic is of special
concern to observers who wear glasses to correct an astigmatism, because a long enough eye relief is necessary
to allow room for glasses.
Short Eye Relief Distance
Eyepiece Lens
Telescope Focal Length
1000mm
Telescope Focal Length
Magnification =
Eyepiece Focal Length
Telescope Focal Length
Focal Ratio =
Telescope Aperture
Exit Pupil (mm)
Eyepiece Lens
Short Eye Relief Distance
Exit Pupil =
Eyepiece Lens
Long Eye Relief Distance
8
Eyepiece Lens
Eyepiece
Focal Length
20mm
Eyepiece Focal Length
Telescope Focal Ratio
Exit Pupil (mm)
ENG
Eyepiece Lens