What Telescope is Best? Will Sager BVAC

Six Things I Think I Think About Scopes There is no perfect scope – different types have different strengthsThere is no perfect scope – different types have different strengths A cheap scope is worse than no scope at allA cheap scope is worse than no scope at all You don’t have to spend a fortune to get a good scopeYou don’t have to spend a fortune to get a good scope A good scope can’t beat a bad skyA good scope can’t beat a bad sky When it comes to aperture, bigger usually is betterWhen it comes to aperture, bigger usually is better Your use of a telescope is inversely proportional to how hard it is to useYour use of a telescope is inversely proportional to how hard it is to use

Telescope Components Optical tubeOptical tube EyepieceEyepiece MountMount FinderFinder Tracking motorTracking motor “Go to” system“Go to” system tube eyepiece finder optics mount motor go to

Telescope Rule of Thumb Need good qualityNeed good quality –Optics –Mount –Eyepiece If any of these are poor, your results will be alsoIf any of these are poor, your results will be also tube eyepiece finder optics mount motor go to

How a Telescope Works Optics gather lightOptics gather light Focus at point to form imageFocus at point to form image Eyepiece allows you to examine image detailEyepiece allows you to examine image detail Both telescope lens (mirror) and eyepiece are rated by aperture and “focal length”Both telescope lens (mirror) and eyepiece are rated by aperture and “focal length” eyepiece objective lens

Telescope Flavors Three main types:Three main types: Refractor – uses glass objective lensRefractor – uses glass objective lens Newtonian reflector – collects light with a curved mirrorNewtonian reflector – collects light with a curved mirror Catadioptric – also collects light with a mirror, but has folded light pathCatadioptric – also collects light with a mirror, but has folded light path

Refractor Light goes from lens directly to the eyepieceLight goes from lens directly to the eyepiece No obstruction in light path – gives high contrastNo obstruction in light path – gives high contrast Most expensive scope per inch of apertureMost expensive scope per inch of aperture Objective lens diagonal eyepiece focuser

Refractor Refractor must have special 2 or 3 element lens if it is to focus all colors of light at same point – or it must have long focal lengthRefractor must have special 2 or 3 element lens if it is to focus all colors of light at same point – or it must have long focal length Apochromatic lens – expensive color corrected objecitveApochromatic lens – expensive color corrected objecitve Refractors also tend to have long tubes, causes wobbleRefractors also tend to have long tubes, causes wobble Takahashi TOA-130 5” objective lens $5500

Newtonian Reflector Concave mirror focuses lightConcave mirror focuses light Secondary mirror pushes light cone to side to the eyepieceSecondary mirror pushes light cone to side to the eyepiece Tube is open; can have air currents (bad)Tube is open; can have air currents (bad) Secondary mirror blocks some light, causes diffraction, and lessens contrastSecondary mirror blocks some light, causes diffraction, and lessens contrast Mirror must be collimatedMirror must be collimated Most Newts have off-axis comaMost Newts have off-axis coma But biggest aperture bang for the buck primary mirror secondary mirror eyepiece spider focuser

Newtonian Reflector Orion 6” Newtonian on equatorial mount - $240 Orion 12” Newtonian on Dobsonian mount - $1000

Catadioptric Reflector Has primary mirror like Newtonian, but secondary mirror folds the light back toward primary Light passes through hole in primary to eyepiece Secondary mirror curved to make scope have longer focal length Some have corrector plate at front to correct optics primary mirror secondary mirror diagonal & eyepiece corrector plate focuser

Schmidt Cassegrain Telescope - SCT Small Meade ETX SCT – 3.5” - with go-to mount - $300 Celestron 11” SCT - with GPS go-to mount - $2800

Most Popular SCT Celestron 8” SCT on half-fork go-to mount - $1500 Meade 8” SCT on fork go-to mount - $1999

Mount Types Altaz – one axis vertical (azimuth) and the other horizontal (altitude) Equatorial – one axis aligned with Earth’s rotation axis (right ascension) and the other perpendicular (declination) Fork – popular mount style for SCT scopes – can be set altaz or equatorial German equatorial – GEM – popular type for many scopes – has one axis pointing at celestial rotation axis (right ascension) and another perpendicular (declination) Altaz Dobsonian Fork-mounted equatorial

Mounts Refractor on GEM Refractor on altaz Newtonian on GEM SCT on GEM Star motion around celestial axis

Eyepieces Eyepieces change the magnification of your telescopeEyepieces change the magnification of your telescope Magnification = focal length of objective divided by focal length of eyepieceMagnification = focal length of objective divided by focal length of eyepiece –Ex: 2000 mm f.l. objective with 20 mm f.l. eyepiece, M=100 Many different types of eyepieces with different lens combinationsMany different types of eyepieces with different lens combinations Most good eyepieces have 1.25” or 2” barrelsMost good eyepieces have 1.25” or 2” barrels Eyepieces must be good quality too

Telescope Power Laws of physics put a limit on resolving power of telescopeLaws of physics put a limit on resolving power of telescope Dawes limit: R = 4.56/DDawes limit: R = 4.56/D –R = limit in arcseconds –D = aperture diameter in inches This says that you need a bigger aperture for higher resolutionThis says that you need a bigger aperture for higher resolution Rule of thumb: 50x per inchRule of thumb: 50x per inch –3-inch objective – 150x –8-inch objective – 400x Practically, atmospheric conditions rarely allow >200xPractically, atmospheric conditions rarely allow >200x High power requires steady mount and trackingHigh power requires steady mount and tracking 90 mm = 3.5” max ~ 175x 200 mm = 8” max ~ 400x

Finder Usually finder is a small telescope mounted on side of big scopeUsually finder is a small telescope mounted on side of big scope Finder scope can be confusing because image is backwardsFinder scope can be confusing because image is backwards Many scopes have a “unit power” finder because it is easy to useMany scopes have a “unit power” finder because it is easy to use

Computerized Mount “go-to” Biggest revolution in telescope mounts in a generationBiggest revolution in telescope mounts in a generation Mount has motors that are controlled by computerMount has motors that are controlled by computer Computer tells mount where objects are locatedComputer tells mount where objects are located Great for finding hard- to-find objectsGreat for finding hard- to-find objects Not idiot-proof. Still need to know some stars for calibrationNot idiot-proof. Still need to know some stars for calibration Newtonian on go-to GEM SCT on go-to fork

Telescope Recommendations Don’t buy a cheap scope – it’s better to have less scope with fewer bells & whistles but with good quality opticsDon’t buy a cheap scope – it’s better to have less scope with fewer bells & whistles but with good quality optics Don’t go too big – don’t go too small (6”-8” sweet spot)Don’t go too big – don’t go too small (6”-8” sweet spot) Go to star parties and look through lots of scopes –talk with other astronomersGo to star parties and look through lots of scopes –talk with other astronomers Don’t want to spend $$? - get a good pair of binoculars (7 x 50)Don’t want to spend $$? - get a good pair of binoculars (7 x 50) Figure out what you want in a scopeFigure out what you want in a scope Keep expectations realisticKeep expectations realistic Nikon 7 x 50 binos $80

Basic Telescope Under $500Under $500 Dobsonian reflectorDobsonian reflector GEM reflectorGEM reflector No frills Orion 6” Newt $240 No frills Orion 8” Dob $370

A Bit Better Under $1000Under $1000 Bigger DobsonianBigger Dobsonian Small go-to SCTSmall go-to SCT Orion 10’ Dob with object locator Celestron Nexstar 6” go-to $999

Pretty Nice Under $1500Under $1500 8” SCT go-to8” SCT go-to 12” Dob12” Dob 6” achromatic refractor6” achromatic refractor Celestron 8” SCT go-to $1299 Meade 8” SCT with go- to GEM mount - $1499 Meade 6” refractor on go-to mount $1200

Conclusions Incredible variety of good telescopes on the marketIncredible variety of good telescopes on the market Look for good quality scopeLook for good quality scope Buy good quality eyepieces and accessoriesBuy good quality eyepieces and accessories –Get a star planisphere and star atlas –Get Sky & Telescope magazine to see what’s going on Read reviews from other astronomersRead reviews from other astronomers Check for used scopesCheck for used scopeswww.astromart.com Learn the sky and how to use your scope. Check local astronomy club for helpLearn the sky and how to use your scope. Check local astronomy club for help Get away from light pollutionGet away from light pollution Turn on your sense of awe and wonderTurn on your sense of awe and wonder