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2. Great Paris Exhibition Telescope of 1900 - Wikipedia

   en.wikipedia.org/wiki/Great_Paris_Exhibition...

   The telescope: overall side view (top); the siderostat (left) and lens tube (right); ocular lens end (inset) The telescope had two interchangeable objective lenses (for visual and photographic use respectively) 1.25 m (49 in) in diameter, with a focal length of 57 m (187 ft).

3. Eyepiece - Wikipedia

   en.wikipedia.org/wiki/Eyepiece

   Many of these eyepieces that come with such telescopes are plastic, and some even have plastic lenses. High-end telescope eyepieces with this barrel size are no longer manufactured, but you can still purchase Kellner types. 1.25 inch (31.75 mm) – This is the most popular telescope eyepiece barrel diameter. The practical upper limit on focal ...

4. List of largest optical telescopes in the 20th century

   en.wikipedia.org/wiki/List_of_largest_optical...

   Ultimately, a valid comparison between two telescopes must take into consideration more specifications, when a general measurement becomes obtuse. Aperture of the primary mirror alone can be poor measure of a reflective telescope's significance; for example, the Hubble Space Telescope has only a 2.4 metres (94 in) primary mirror. In addition ...

5. Advanced Combat Optical Gunsight - Wikipedia

   en.wikipedia.org/wiki/Advanced_Combat_Optical...

   The technique is essentially using the illuminated part of the reticle and its focusing rear eyepiece as a collimator sight. [14] As in any other collimator sight, the user does not actually look through the sight but instead keeps the collimated (infinity) image of the illuminated part of the reticle in focus with the dominant eye while the ...

6. Star diagonal - Wikipedia

   en.wikipedia.org/wiki/Star_diagonal

   A star diagonal, erecting lens or diagonal mirror is an angled mirror or prism used in telescopes that allows viewing from a direction that is perpendicular to the usual eyepiece axis. It allows more convenient and comfortable viewing when the telescope is pointed at, or near the zenith (i.e. directly overhead). Also, the resulting image is ...

7. List of largest optical refracting telescopes - Wikipedia

   en.wikipedia.org/wiki/List_of_largest_optical...

   The Swedish 1-m Solar Telescope, with a lens diameter of 43 inches, is technically the largest, with 39 inches clear for the aperture.The second largest refracting telescope in the world is the Yerkes Observatory 40 inch (102 cm) refractor, used for astronomical and scientific observation for over a century.