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  1. #1
    bizkit_'s Avatar
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    Default I want to buy a telescope or a binocular...?



    but I don't know what does for example 140/900 for telescopes or 20x70 for binoculars mean. How many times can you zoom in with this?

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    In binoculars, the first number is the magnification, and the second is the diameter of the objective (front) lenses in millimeters. Telescopes are specified in a variety of ways. The most important specification for a telescope is the aperture (objective size), which is the diameter of the main lens or mirror. 140/900 indicates a telescope with a 140mm (5.5") objective, and a focal length of 900mm. Another way of specifying this would be 140mm f/6.4. "f/6.4" is the focal ratio, meaning the focal length is 6.4 times the aperture. The focal length gives you some idea of how long the telescope is (in most cases), and is also used in computing the magnification of various eyepieces. Magnification = (telescope focal length)/(eyepiece focal length). Focal length has little effect on the performance of the telescope.

    Beware of telescopes advertised by magnification. These are cheap telescopes being marketed to the ignorant.

  3. #3
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    If u are on a buget buy really good binoculas-proffesional ones from a speciality astronoy store.

    if not, for starting out, best telescopes are the SkyQuest Dobsonian Reflector Telescope.

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    Default

    20 x 70 means that the binoculars magnify twenty times and that they have lenses that are 70mm diameter. That would be a nice pair of astronomical binoculars. As for telescopes, they usually have one number in the name, such as "nexstar 6". The "6" is the aperture in inches. Magnification on a telescope depends on the focal length and the chosen eyepiece.

    The140/900 telescope sounds like 140mm and magnification of 900. Because it is given these kinds of numbers, I would guess that it is an inexpensive "toy" scope. Those manufacturers try to sell them on the basis of huge magnification, hence "900". I wouldn't buy it. The important thing is aperture, not magnification.

 

 

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