WelcometoAstronomyWorkshop
SponsoredbyTheSaintJohnAstronomy
Club
AstronomyWorkshop
• Howtouseyourtelescope• Telescopedesigns• Howtochoosetherighttelescopeforyou• Accessoriesandtheiruse• Whatyouneedtoobserveortakepictures• Howtouseaplanisphere• Whatisinthenightskyeachmonth
YourFirstTelescope
• Astronomyisan immenselyrewardingadventure fullofexplorationanddiscovery.Planets,stars,nebulaeandgalaxiesareawaitingtoinspireyou.Buyingyourfirsttelescopeisnotalwayseasy.We’lltakealookatthefourmostcommontype’softelescopesandhowtheyworktogiveyouabetterideaofwhatmaybebestforyou.
Whoinventedthetelescope?
• GalileoGalilei• SirIssacNewton• Copernicus• HansLipperhey
GalileoGalilei
Dateofbirth:1564-02-15Dateofdeath:1642-01-08Birthplace:Pisa,DuchyofFlorence,Italy
Historyofthetelescope• Intheearly1600’sDutchlensgrinderHansLipperhey,appliedtopatentadevicetomakedistantobjectsappearcloser.Thuswasborntherefractortelescope.
• In1609GalileoGalileiheardthisdevicewasrealanddecidedtoimproveonthedesign.Thefirstdeviceswereonlyabout3xpowerbutGalileo’searlyattemptsgave8xpowerviewing.ThisiswherethefirstrealevidenceofmountainousregionsonthemoonwasobservedandalsowasresponsiblefordiscoveringJupiter’sfourmoonsknowtodayastheGalileanMoons.
WhocannamethefourGalileanMoons?
TheFourGalileanMoons
• IO
• CALLISTO
• EUROPA
• GANYMEDE
Galileo’stelescopedesigndesigned8x,20xandfinally30xpower
Re-creationofGalileo’stelescope
Today’sTelescopeDesigns
Lightpaths/optics
• http://www.stargazing.net/naa/scope2.htm
Reflecting/Refractorlightpaths
Refractordesign(Galilean)
SirIsaacNewton
Newtonian(SirIssacNewton)Reflectordesign
JohnDobsonTheDobsonianDesign
JohnDobsonJohnDobson in2002.
Born JohnLowryDobsonSeptember14,1915Beijing, China
Died January15,2014 (aged 98)Burbank,California, U.S.
Nationality AmericanOccupation Vedantan
monk (1944−1967),lecturer/popularizerof amateurastronomy[1]
Known for Dobsoniantelescope, sidewalkastronomy
Today’sDobsonianReflector
Schmidt-CassegrainDesignCatadioptric
Verycompactdesignwithlongfocallength
Whatarethepro’s andcon’s ofeachtelescopedesign
• Refractor• Pro’s Classicdesign,Noobstructions,goodcontrast,Nocollimation(usually),Nothermaldegradation.Excellentforimaging
• Con’s Expensiveperaperture,Largerscopesverylong,Chromaticaberrationinlessexpensivemodels.
Newtonian /Dobsonian
• Pro’s Inexpensivetomanufacture,largestaperture,nochromaticaberration,variousdesignsavailable,Dobsoniandesignaswell.
• Con’s Requirescollimation,opendesignrequiresmaintenance,verylargetohandleonmounts,mustchoosefocuserbasedonobservingorimaging,coma(imaging)
SchmidtCassegrain
• Pro’s Verycompact,verypracticalhandling,portable,viewingisalwayscomfortable,veryflexiblewithaccessories,setsupveryquickly(forkmount)Con’sCanbeveryexpensive,longcoolingtime,largerprimarymirror,requirescollimation(notasmuchasNewtonian)
Accessories foryourOTA
Eyepieces,diagonals,finderscopes,solarfilters
StarDiagonals
RequiredforrefractorsandSCT’sforviewcomfort
Whatisastardiagonal?• Mirror(reflective)diagonals: Thesediagonals(oftencalledStar
diagonals)usea mirror setata45° angleinsidethediagonaltoturnthetelescope’simageata90° angletotherearcell.Mirrordiagonalsproduceanimageinthe eyepiece thatiscorrectlyorientedvertically,butisreversedleft-to-righthorizontally.Thiscausesimagereversal,theviewintheeyepieceisflippedleft-right.Themajoradvantagetomirrordiagonals isthattheycostlesstoproducetoahighdegreeofopticalaccuracy comparedtoaprismandthattheydonotintroduceanycolorerrorstotheimage. Themajordisadvantageofmirrordiagonalsisthatunlessthereflectivecoatingisproperlyappliedtheycanscatterlightrenderinglowerimagecontrastcomparedtoa90-degreeprism.Alsotheydeterioratewithageasthereflectivesurfaceoxidizes.ThenewerDielectricmirrorshavelargelysolvedthedeteriorationproblem,andifproperlymadetheDielectricmirrorsscatterlesslightcomparedtoconventionalmirrors.
Thepathoflight
Allowsmuchmorecomfortableviews
Flexiblediagonals
Finderscopes
Eyepieces• WhatTypeofTelescopeEyepieceShouldYouBuy?
Whatsortofeyepiece,then,shouldyouuse?Acasualinspectionofmostpublicationsadvertisingopticalaccessorieswillrevealaplethoraoftypes— almostasmanyvarietiesastelescopes,itseems!Choosingtherightoneforyoudependsonseveralfactors:theobjectsyouwishtoobserve;howtolerantyouareofopticalimperfections;whetheryouwantnarroworwidefieldsofview;whetherornotyouwearglasses;and(asalways)howmuchyouarepreparedtospend.
WhichOne?????
EyepieceDesigns
• EyepieceTypes• Somenames,like Ultrawide,giveacluetoaneyepiece'sprincipalcharacteristics.OthershaveclassicnameslikeKellner,Orthoscopic,Plössl,andErfle,ormorespecificmodernvariantslikeNagler andLanthanum. Opticalaberrations (deviationsfromthe"ideal"form)arebettercorrectedinsomedesignsthanothers,butlikeeverythinginlife,thehighertheprice,thebetterthequality.
Costeffectiveeyepieces
• Evenso,eyepieceswithdesirablecharacteristicsstillcanbeobtainedatreasonablecostonceyouknowwhattolookfor.Atthebudgetendofthemarket,three-element(meaningtheyhavethreelensesinside)eyepieceslabeledKellneror"MA"(modifiedachromat)canturninagoodperformancewithscopesoflongfocalratio,suchasSchmidtCassegrainsandtraditionalrefractors.Theydonotworkwellwithtelescopesofshortfocalratio.
MeadeMA(modifiedachromats)
KellnerThe3-elementKellnergivessharp,bright imagesatlowtomediumpowers.Bestusedonsmalltomedium-sizetelescopes,Kellners haveapparentfieldsaround40degrees�andgoodeyerelief,thoughshortathigherpowers.Good, low-costperformerdesign.
Intermediateeyepieces• Foroptically"fast"Newtoniansandthelike,betterresultswillbeobtainedwithfour-elementdesigns,suchastheslightlyout-of-fashionbutotherwisedesirableOrthoscopic,orthePlössl.Thelatterisagoodall-rounder,particularlywhenantireflectionmulticoated.APlösslcandeliverwell-corrected,widefieldsofviewwithgoodeyerelief—meaningtheeyecanbepositionedatacomfortabledistancebehindtherearlensandstillseethewholefieldofview. Itisworthpointingoutthatobserverswhowearglassestocorrectforsimplelong- orshort-sightedness(noastigmatism)don'tneedtousethematthetelescope;atwistofthefocuserwillremedythat.
Plossl
PlosslToday'smostpopulardesign, the4-elementPlossl providesexcellentimagequality,goodeyerelief,andanapparentfieldofviewaround50degress�.High-qualityPlossls exhibithighcontrastandpinpoint sharpnessout totheedge.Idealforallobserving targets.
Premium/widefieldeyepieces• High-powerlunarandplanetaryviewingentailstheuseofshort-focal-lengtheyepieces.Thishasspawnedthedevelopmentofsix- toeight-elementdesignsthatcombinecomfortableeyereliefandwideapparentfields.Theymayfeatureexoticrare-earthglasselementstoreduceopticalaberrationsstillfurther.ManyregardtheseLanthanumandUltrawidedesignsasthepinnacleofeyepieceevolution,butformanypeoplethepricewillbeabarrier— andtheirphysicalsizeandweightmaybeanissuefordelicatelybalancedsmallscopes.
PremiumWideAngle
UltrawideTypesVariousimproveddesigns incorporating 6to8lenselementsboastapparentfieldsupto85-100degrees� - sowideyouhavetomoveyoureyearound totakeinthewholepanorama.Lighttransmission isslightlydiminished, butotherwise theimagequalityintheseeyepiecesisveryhigh.Sotooistheirprice.
CoatingsonLenses• OpticalcoatingsinlensesarealmostalwaysmadeofMagnesium
Flouride(MgFL).Theyareappliedinavacuumchamber.Asingleopticalcoatingshouldhaveaverysubtlebluecolorwhenyoulookatthelenssurfaceatanangle.Multi-Coatswillhaveagreenorevenpurpletintwhenyouexaminethesurface.
• Inall,thereareseveralacceptedclassificationsforopticalcoatings:
• Coatedmeansthatatleastoneair-to-glasssurfaceintheopticalsystemhasanopticalcoating.
• FullyCoatedmeansthatallair-to-glasssurfacesintheopticalsystemhaveanopticalcoating.
• Multi-Coatedmeansthatatleastoneair-to-glasssurfaceinthesystemhasanopticalmulti-coat.Therestshouldhaveatleastasingleopticalcoating.
• FullyMulti-Coatedmeansthatallair-to-glasssurfacesinthesystemhavemutli-coatings.
BarlowLenses
WhiletheBarlowisnotstrictlyaneyepiece,anenormouslyvaluableaccessory.ABarlowisinsertedintothetelescope'sfocuserbeforetheeyepieceanddoubles(ortriples,insomeinstances)themagnification.Attheexpenseofasmalllossoflight,thisveryusefuldevicecandoubleyoureyepieceinvestmentbymakingeachperformattwopowers.Givesomethoughttostaggeringthefocallengthssothattheyarenotsimplemultiplesofoneanother:a10mmeyepiece islargelyredundantifyouusea20mmandaBarlow.
Barlowlenses
• BarlowsSaveYouMoneyUsedwitha2xbarlow,your40mmeyepieceeffectivelybecomesa20mmeyepiece.Inatelescopewitha1000mmfocallength,the40mmeyepieceyields25xmagnificationaloneand50xmagnificationwhenusedwitha2xbarlow.A10mmeyepieceyields100xaloneand200xwithabarlow.Soabarlowlensessentiallydoublesthenumberofeyepiecesinyourcollection-agreatmoney-savingstrategy.
Whatdothenumbersmeanonmytelescope?
•SpecificationsoftheFirstscope80EQRefractor:Aperture 80mmFocalLength900mmFocalRatiof/11ComputerControl- no1.25"Eyepieces:FocalLengths20mmand10mmMagnificationLevels:90xand45xFinderscope:StarPointerTripod:AluminiumadjustableMount:equatorialWeight:24lbs.MulticoatedopticsCanbeusedforbothterrestrialandastronomicalviewing
Aperture• Aperture80mm
Thediameteroftheobjectivelensis80mm,whichis3.1inches.
• Theobjectivelensisthelargelensthatcaptureslightandfocusesitintoanimage.Thebiggertheobjective,themorelightthetelescopecangatherwhichinturnmeansthatfainterobjectscanbeobserved.Thesizeoftheobjectivedetermineswhatmagnificationthetelescopecanachievewithoutlosingresolution.Aquickruleofthumbis50timesthediameteroftheobjectiveininches.So,youcouldreasonablyexpectthistelescopetomagnifyimages~150times(50x3.1)beforeresolutionisaffected.
FocalLength
• FocalLengthThefocallengthisthefocallengthoftheobjective;thedistanceneededbytheobjectivetobringallthelightcollectedtoafocus.Soforthistelescope,animageisformed900mmfromtheobjectivelens.Youwillneedthisnumberwhenyouareworkingoutmagnification - moreonthisunder eyepieces .
FocalRatio• FocalRatiof/11Sometimesknownasthef/number.Focalratiosarethefocallengthdividedbythediameter,henceforthistelescope:900mm̧ 80mm=11,writtenasf/11.
• Aquickruleofthumbis:f/10andhigher:smallerfieldofview;goodforlookingatthemoon,planetsanddoublestarsf/8:intermediateandgoodforgeneralallroundviewingf/6andbelow:widerfieldofview;goodfordeepskyobjects
MagnificationFormula• Magnification• Themagnificationofanastronomicaltelescopechangeswiththeeyepieceused.Itiscalculatedbydividingthefocallengthofthetelescope(usuallymarkedontheopticaltube)bythefocallengthoftheeyepiece (bothinmillimeters).Thus:
• TELESCOPEFOCALLENGTH/OCULARFOCALLENGTH=MAGNIFICATION
• Forexample,atelescopewitha1000mmfocallengthusinga10mmocularisoperatingat100xmagnification(1000/10=100).
FocalRatio(F5,F7,F10ect)• FocalRatio(f/stop)• Thefocalratio,orf/stop,ofanylenssystem(includingtelescopes),iscomputedbydividingthefocallengthbytheclearaperture(usuallyexpressedinmillimeters).Inotherwords,thefocalratioistheratioofthefocallengthandclearaperture.Thus:
• TELESCOPEFOCALLENGTH/CLEARAPERTURE=FOCALRATIO
• Forexample,atelescopewithafocallengthof1000mmanda100mm(4")clearaperturehasafocalratiooff/10(1000/100=10).
FieldofViewFOVinDegrees
Whatdothenumbersmean?
KnowtheNumbersWhenshopping forabinocular, buyerswillfindbinocularsarecategorizedbyasetofnumbers, suchas 7x35mm;read"sevenbythirty-fivemillimeters."Otherbinocularsmightrangefromatiny3x14mmtogiantbattleshipbinocularsthatare40x178mm.Thesetwonumbers representmagnificationandobjectivelensdiameter.Thesetwoaspectsareimportanttounderstandwhenselectingbinoculars.
Binoculars
Magnification:
Consider thisgeneralruleaboutoptics:lowmagnificationprovidesawidefieldofviewandiseasytoholdsteady.Soalthoughamagnificationof10,12orhigher isavailable,6,7,and8-powerbinocularsareeasiertouseandinmanycasesmorepractical.
LensDiameter:Thesecondnumber ina7x35mmpairofbinoculars indicatesthelensdiameter.Thelensdetermineshowmuchlightisgathered,andthereforedetermines thebrightnessofviewing. Thebigger thelensmeansthegreaterthelightcapacity,andthebrighter theview.However,thebigger lensmeansabiggerandbulkierbinocular.Generally,lensesbelow30mmaredefinedasminibinoculars.
BinocularTypes• Therearefourmaintypesofbinoculars:twotypesofstandardsizesandtwotypesof
smallersizes.Understanding thesemaintypeswillhelpbuyerstonarrowtheirsearchtothetypebinocular thatfitstheirneeds,budget,andpreference.
• MiniBinoculars• Thesearethesmallestcategoryofbinoculars.Asdiscussedabove,thesegenerallyinclude
objectivelensesnotlargerthanabout1inchindiameter,andtheyhavethestraight-lineroofprismdesign.Minibinocularsaredesignedspecificallyfortravel,andthereforearefoldable, lightweight, andhighlyversatile.Becauseoftheirrelativelysmallobjectivelenses,minibinocularsaregenerallynotintendedforhigh-resolutionactivities,suchasbirdwatching.
• Compactbinoculars areslightlylargerthanminibinoculars,butsmallerthanregular size.ThesebinocularsutilizethePorroprism,whichmakesthembulkierthanminibinoculars,buttheystillhaveanobjectivelensthatisthesamesizeastheminiversion.Compactbinocularsarepopular forsporting eventsorasageneral-purpose travelbinocular.Compactsprovideagoodtrade-offbetweenweight,performance,andcost.
• StandardPorroPrismBinoculars• Thisiswheremoststandardbinocularsfall.Thesehavealargerobjectivelens,andarea
generalbinocularforuseineverything fromsportingeventstohuntingand aremoderatelypricedandhighquality,availableinawiderangeofspecifications.
• Thestandard RoofPrismbinoculars areamoreprofessional-levelbinocularforadvancedapplications,suchasforseriousbirdwatchers. Thesebinocularshaveasleek,straight-linestyle,thefinestopticalglasses,andmulti-elementeyepieces.Theyprovideabright,sharp,andhigh-resolutionimagethatishigherqualitythanotherbinoculars.
Planispheres
NowtheHandsOn!!
FirstStep:AlignFinderScopewithMainScope
• Step1:Setupscope• Step2:RemoveCover(lol)• Step3:Chooseastilltarget(ifstarusePolaris)• Step4:Selectlowpowereyepiece• Step5:Pointscopeattarget(centerinFOV)• Step6:Usingfinder,centertargetwithknobs• Step7:Lookthrougheyepieceforaccuracy• Step8:Usehigherpowereyepieceandrepeat
AcclimateYourScope
Whyaremyviewsblurry?•TUBECURRENTTubecurrentsaretemporaryaberrationsthatcansometimesbeagreatproblem.Coolingdownatelescope(totheoutsidetemperature)beforeaviewing-sessionshouldnotleavemuchroomforthisproblem.Sometelescopes(closedCatadioptrics,SCT/MCT)sometimesneedalongcooldownorevendon’treachequilibriumduetoafastcoolingfromevening-temperaturetonight-temperature.
Collimation
BalanceYourScope
WhydoIneedtoBalance
• BalancingtheTelescope:
ToeliminatestressesontheEquatorialmountsandtoensuresmooth,judder-freemotionofthetelescopetheinstrumentneedstobebalancedaboutboththedeclinationandpolar(rightascension)axis.Thisisespeciallyimportantifyouproposetouseamotordriveforastrophotographyatafuturedate.