INSTRUMENTS

ASTRAL TELESCOPE

BASIC NOTES

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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 also possible.
(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 and planets.

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 photography.
They are luminous enough for use in photography, and permit a conveniently high level of magnification.
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.