Education

Best Solutions for Choosing the Perfect Telescopes

Beginner
instruments most often have a diameter between 60 and 150 mm (60 to 80 mm for a
telescope, 100 to 150 mm for a telescope). After a few years, deep sky
enthusiasts begin to dream of large diameter telescopes (250 mm or even 400 mm)
to hunt the most distant galaxies or the pale nebulae that barely stand out
from the sky.

  • Simulation of an observation of
    the Moon with two instruments of very different diameters (60 mm and 300 mm). The
    diameter of a telescope affects both clarity and level of detail. This
    simulation was carried out with the Stelvision simulator which you can use
    yourself to evaluate what it is possible to see in a telescope according to its
    diameter.

As for the focal , it has an influence on:

The
magnifications obtained, stronger with a long focal length (but be careful, we
will see later that a strong magnification is not always desirable).

The size of the instrument

A conventional
telescope is always quite long : its focal length is around 10 to 13 times its
diameter, for example 700 mm for a diameter of 60 mm. It is a condition for
providing good images within a reasonable budget. Indeed, most glasses suffer
from a defect called chromatic aberration which causes the appearance of
colored borders at the edge of the image and a loss of sharpness . This
phenomenon is negligible in the case of long glasses and more marked in the
case of short glasses (except for certain very expensive models which use a
sophisticated optical design). Now with the Best Telescope For Viewing Planets And Galaxies
you can find the best deal here.

A Newton type
telescope can have a short focal length for example 5 or 6 times its diameter,
for example 1200 mm focal length for a diameter of 200 mm, as long as its main
mirror is a true parabolic mirror – and not a spherical mirror found on
inexpensive models.

What magnification?

Let us first
clarify that magnification is not a real criterion for choosing a telescope or
an astronomical telescope . Indeed, the magnification depends on the eyepiece
used. An instrument is always delivered with several eyepieces and additional
eyepieces can also be purchased separately to complete its range of
magnifications. We can therefore consider the magnification as an adjustable
parameter.

Then, it is
important not to believe that an astronomical instrument should grow as much as
possible. Because low or moderate magnifications can be much more appropriate
than high magnifications in many cases. Indeed:

  • High magnification makes the
    image less bright
  • It makes you lose sight of
    everything by narrowing the field of vision

it may lead to a
blurred image due to the limited resolution of the instrument; this limitation
is inversely proportional to the diameter, so that in general we avoid any
magnification greater than 2 times the diameter of the instrument in
millimeters; often, a magnification limited to 1 or 1.5 times the diameter is
preferable.