Talking Telescopes Geoff Gaherty
Introduction When to buy? Telescopes Mounts Eyepieces Accessories Recommendations
When to buy? Get to know the sky first Consider buying binoculars first Sample other people’s telescopes first Do some research first (the fun kind!): Reading: Harrington: Star Ware (Wiley) Online: Star parties Then…go shopping (at a telescope store!)
Telescopes Types: refractor reflector catadioptric Properties aperture focal length focal ratio Pros and cons
Telescope types Refractor: lens achromatic apochromatic Reflector: mirror Newtonian Catadioptric: mirrors with corrector lens Schmidt-Cassegrain Maksutov-Cassegrain
Telescope properties Aperture = diameter of lens/mirror/corrector determines resolution and light gathering Focal length = effective distance from lens/mirror to eyepiece determines magnification and physical length Focal ratio = focal length / aperture mainly for astrophotographers
Telescope pros and cons Refractor: simple maintenance high contrast expensive Reflector: “best bang for the buck!” Catadioptric: compact size “astrophotography ready”
Mounts Altazimuth Dobsonian simple operation Equatorial two types: German and fork automatic tracking require polar alignment Computerized?
Computerized mounts Manual simple, no batteries required Digital setting circles (DSCs) computer guided/manually powered fast, quiet, low power consumption GoTo computer guided/motorized slower, noisier, high power consumption
How do you find things without a computer? Learn the constellations Starhopping figure out the route in a star atlas start from a known bright star practise the route with binoculars retrace the route in the finder scope Consolmagno & Davis: Turn Left at Orion (Cambridge) Phil Harrington: Star Watch (Wiley)
Eyepieces Types: Plössl, orthoscopic, wide field Properties: focal length: determines magnification = telescope f.l. / eyepiece f.l. field of view: apparent vs true eye relief: where to place your eye? exit pupil: light output
Magnification Depends on aperture and seeing conditions Typically: Low power ≈ aperture (mm) / 5 10-inch aperture (250 mm): 50x Medium power ≈ aperture / 2 10-inch aperture (250mm): 125x High power ≈ aperture (mm) 10-inch aperture (250 mm): 250x Maximum ≈ 300x limited by atmospheric stability
Accessories Binoculars (10x50) Barlow lens (2x) Red flashlight (Rigel) Star atlas: Pocket Sky Atlas (Sky) Book: Dickinson: NightWatch (Firefly) Software: Starry Night
Recommendations 10-inch reflector Dobsonian mount No computer/Digital setting circles All of the above accessories