INSTRUMENTS

ASTRAL TELESCOPE

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OCULARS AND MAGNIFICATION

N.B. Every time you want to focus on an object, always use the finder first, as this has a greater visual field and can speed up your preliminary operations. Always begin your observation of an object with an ocular of lesser magnification and then pass on, if you wish, to one of greater magnifying power. Substitution of the oculars will always necessitate altering the focus. Do not forget that the images given by the telescope are reversed (or flipped) whether from side to side or from top to bottom. This is normal when using an astronomic telescope, because in the observation of the stars it makes absolutely no difference, while at the same time allowing you to reduce costs. Later we shall explain how to observe terrestrial objects with a straight image.
Never observe through the glass of a window, always choose open spaces away from heat sources in the path of the objects under observation.

OCULARS AND MAGNIFICATION
Every  telescope comes equipped with one or more oculars of different focal lengths (for example a K9mm and a H20mm). The magnification of each ocular depends directly on the focal length of the telescope, indicated by the number that follows the letter "f'. For example, a telescope on which is found D. 114 F 1000 will be an instrument with a focal length of 1000 (the first number indicates the diameter of the objective or of the mirror). The magnification will be obtained with the following formula.

For example, in the case of a telescope with a focal of l000mm and an ocular of 20mm the magnification will be as follows: 1000:20=50x (magnification of 50 rimes the original).
The Barlow lens doubles the magnification of ail types of ocular. (fig.3) A vast range of oculars with different focal lengths exists, and this allows you to vary the magnification offered by the telescope. In ail cases, however, it is better not to exceed the practical limits of twice the diameter in millimeters of the instrument.
Oculars are among the most important of the telescope accessories, in that they give us the possibility of varying the level of magnification and the field held within the frame according to the type of object under observation and to the condition of the sky. The symbols placed in front of the focal value identify the optic scheme:
*H = Huygens, with only two lenses. The quality is good in the center of the fieId.
*AH = Achromatic Huygens, with three lenses. Better quality in ail the field, generally used for long focals.
*HM = Modified Huygens, with two lens, but with a slightly better quality than the classic Huygens.
*K = Kellner, with three lenses, average field and good quality.
*OR Orthoscopic, with four lenses, average field and excellent quality.