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Bagaimana untuk memilih telescope utk beginner 16 Disember 2009

Posted by azmirul in Astronomy.

For info, ni aku summarize daripada website kat bawah:

  1. Galileo Refractor (use lens) vs Newton Reflector (use mirror to collect light)
  2. Alt-Azimuth mount (up/down left/right) vs equatorial mount (for planet/star tracking
  3. Telescope apperture size (bigger is better, more light)
  4. Eyepieces (barrel size 1.25″ (standard), 0.965″, 2″)
    – 25mm focal length give lower magnification than 10mm
  5. Magnification = telescope focal length / eyepeice focal length
    – 20x-50x (wide-field views),   75x-200x (moon, planets, nebula)
    – In astronomy telescopes, clarity is more important than high magnification.
  6. Focal ratio (f-ratio) = telescope focal length / aperture size
    eg. Orion Apex 90mm with 1250mm mempunyai f/13.9 (1250/90)
    – Low focal ratio (f/4 – f/8): wide-angle view
    – High focal ratio (f/8 – f/15): sharp image, good contrast, best for light polluted skies, best for planets, moon, etc.
    Exit Pupil = eyepeice focal length / telescope f-ratio
    – to see clearly, images must not be larger than pupil size (5mm-7mm) or larger magnification will be lost
    – ideal exit pupil for higher magnification = 0.5-1mm
  7. Computerized or manually controlled telescope

Yang ni pulak ringkasan daripada website berikut:

  1. Aperture
     – 4″  (100mm) = star clusters as fuzzy spheres of light
     – 6″  (150mm) = fuzzy spheres become individual faint stars
     – 12″ (300mm) = stars become clearly define
  2. Magnification
     – should be no greater than 50x per inch of aperture (or 2x per mm)
     – eg: max magnification for 4″ telescope = 4*50 = 200x (or 100mm*2)
  3. Type:  Refractor/Reflector/ Schmidt-cassegrain
  4. Coating & Focal Length
     – short focal length (400mm-700mm) = wider field of view
     – higher focal length = planetary studies
  5. Eyepiece Magnification
  6. Finder Scope (5x-8x for wide field viewing area)
     – 5×24 finder scope bermaksud 5x magnification with 25mm aperture
  7. Portability
  8. Mountings – Altazimuth (simple up/down left/right) vs Equatorial mount (tracking planet/star)
  9. Setting Circles (find star chart coordinates)
  10. Tripod – good Damping time (5-6 seconds)
  11. Sporting Scopes (perfect for bird and nature studies)
     – eg 4″ refractor/ Smith-Cassegrain telescope for nature studies
  12. Sugesstion for beginner
     – 80mm refractor (4.5″)
     – 6″ equatorially mounted reflector telescope offer more features
     – 8″ Schmidt-Cassegrain perfect for serious fieldwork


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