This telescope could, in theory, distinguish objects, the separation of
which is 1,43" and, having an aperture ratio of 1/12.5. It is suitable for visual
observation in particular of planets, the sun and the moon of which photography shots are
(100x means magnified by 100, and is read by one hundred).
TELESCOPES WITH A LOW FOCAL RATIO (BE-
TWEEN F/3.6 AND Ftt5): have a large field of vision and are photographically bright. That
means that their low focal ratio permits photographic exposures in a short time span.
These telescopes are not, in general, suitable for high magnifications, but they give good
images over a wide field of weak objects as well as mid-level magnification of the moon
TELESCOPES OF HIGH FOCAL RATIO (BETWEEN F/Il
AND F/16) give high magnification with longer focal oculars. They are easier to use, and
usually give well contrasted images, whether in simple observation or as shown by results
obtained in photography, both of the surfaces of the moon or planets as well as of
terrestrial objects. These telescopes, in terms of photography offer less luminosity and
are not, in general, suitable for long exposure astro-photography of weak objects.
TELESCOPES OF MID-LEVEL FOCAL RATIO (BE-
TWEEN F/6 AND F/10): embrace characteristics of both of the above mentioned categories.
These telescopes are suitable for all types of observation, both visual or for
They are luminous enough for use in photography, and permit a conveniently high level of
It is important to know that the ratio of low focal ratio telescopes can be increased by
means of a Barlow lens, an accessory which shall be mentioned again later.