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  2. Eye relief - Wikipedia

    en.wikipedia.org/wiki/Eye_relief

    The eye relief of an optical instrument (such as a telescope, a microscope, or binoculars) is the distance from the last surface of an eyepiece within which the user's eye can obtain the full viewing angle. If a viewer's eye is outside this distance, a reduced field of view will be obtained.

  3. Exit pupil - Wikipedia

    en.wikipedia.org/wiki/Exit_pupil

    The small exit pupil of a 25×30 telescope and large exit pupils of 9×63 binoculars suitable for use in low light. For a telescope, the diameter of the exit pupil can be calculated by dividing the focal length of the eyepiece by the focal ratio (f-number) of the telescope. In all but the cheapest telescopes, the eyepieces are interchangeable ...

  4. Relay lens - Wikipedia

    en.wikipedia.org/wiki/Relay_lens

    In optics, a relay lens is a lens or a group of lenses that receives the image from the objective lens and relays it to the eyepiece. Relay lenses are found in refracting telescopes , endoscopes , and periscopes to optically manipulate the light path , extend the length of the whole optical system , and usually serve the purpose of inverting ...

  5. Refracting telescope - Wikipedia

    en.wikipedia.org/wiki/Refracting_telescope

    A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens as its objective to form an image (also referred to a dioptric telescope). The refracting telescope design was originally used in spyglasses and astronomical telescopes but is also used for long-focus camera lenses .

  6. Telescopic sight - Wikipedia

    en.wikipedia.org/wiki/Telescopic_sight

    By means of a mathematical formula "[Target size] ÷ [Number of mil intervals] × 1000 = Distance", the user can easily calculate the distance to a target, as a 1-meter object is going to be exactly 1 milliradian at a 1000-meter distance. For example, if the user sees an object known to be 1.8 meters tall as something 3 mils tall through the ...

  7. Magnification - Wikipedia

    en.wikipedia.org/wiki/Magnification

    A telescope, which uses its large objective lens or primary mirror to create an image of a distant object and then allows the user to examine the image closely with a smaller eyepiece lens, thus making the object look larger. A microscope, which makes a small object appear as a much larger image at a comfortable distance for viewing. A ...

  8. Infinity focus - Wikipedia

    en.wikipedia.org/wiki/Infinity_focus

    In simple two lens systems such as a refractor telescope, the object at infinity forms an image at the focal point of the objective lens, which is subsequently magnified by the eyepiece. The magnification is equal to the focal length of the objective lens divided by the focal length of the eyepiece. [1]

  9. Filar micrometer - Wikipedia

    en.wikipedia.org/wiki/Filar_micrometer

    A filar micrometer attached to a telescope. A filar micrometer is a specialized eyepiece used in astronomical telescopes for astrometry measurements, in microscopes for specimen measurements, and in alignment and surveying telescopes for measuring angles and distances on nearby objects.