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Eyepieces&ObservationalTechniques

PAANoviceClass#8March6,2020BrettHardy

Whatisaneyepiece?•  Opticaldevicecomposedoftwoor

moreglasselements•  Providesamagnifiedview•  Magnificationisdeterminedbythe

focallengthoftheeyepiece(mm)•  Thesmallerthefocallength,the

greaterthemagnification•  Magnificationchangesby

telescope•  Magnification=Telescopefocal

length÷Eyepiecefocallength•  1,400mm÷26mm=53.8x•  1,400mm÷8.8mm=159x•  Increasingmagnificationgivesa

largerimage•  Increasingmagnificationgivesa

smallerfieldofviewanddimmerobject

FieldofView•  Amountofskyseenthroughan

eyepiece=truefieldofview•  Apparentfieldofviewisadesign

characteristicofaneyepiece•  Narrowapparentfieldofviewvs.wide

apparentfieldofview•  Remember,fieldofviewisalsochanged

withmagnification•  AFoVrangesfrom40°to110°•  Actualfieldofview(truefield)=

Apparentofview÷magnification•  Forexample:22mmPanoptichas68°

AFoVand64x(1,400÷22=64)•  ActualFieldofView=68°÷64x=1.06°

82° 50°

EyeRelief•  Lightconeorexitpupildistance

fromaneyepiece•  Eyereliefdeterminesthe

comfortableeyedistancefromaneyepiece

•  Eyepieceswithsmallfocallengths(higherpower)haveshortereyerelief

•  >25mmcanbeaproblem•  Glasses•  Astigmatism

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EyepieceQuality•  Yougetwhatyoupayfor☺"  Fit&finish"  Sharperimages"  Highercontrast"  Lessghostingandflaring"  Numberofelements"  Coatings"  Eyecup•  Apparentfieldofview•  Opticalaberrations

EyepieceBarrelSize•  Designedtofitfocusers•  Twostandardsizes:1.25”&2”•  0.965”aretobeavoided•  1.25”aremorecommon•  2”generallyforlower

magnificationwidefieldviews

Barlows•  Twodifferentbarrelsizes•  2xbarlowismostcommon•  Chosenwisely,abarlowcandouble

youreyepieces•  40mm,26mm,10mm+2xbarlow

=20mm,13mm,5mm•  Placingbarlowaheadofthe

diagonalgives~50%moremagnification

Diagonal•  Twodifferentbarrelsizes•  Comfortableviewingangle•  2”to1.25”adapter?•  Mirrorreversedimage

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Recommendations•  Standardkit:

1low(25-90x)1medium(100-175x)1high(180x>)•  2”lowmagnificationwidefield•  Atleastonepremiummedium

powereyepiece•  Optimummediumpowereyepiece

=focalratiooftelescopex2•  Forexample:f/8x2=16mmMagnification=1,400÷16=87.5x•  Qualitybarlow•  Qualitydiagonal•  Neutraldensityfilter•  Purchasebestbudgetpermits•  Getagoodcase

PurchasingEquipmentOntarioTelescope&AccessoriesKWTelescopeFocusScientificAmazonMeadeCelestronTeleVueVixenOrionExploreScientificWilliamOpticsUsedMarketPAAMembersCanada-WideAstronomyBuy&Sellhttps://www.astrobuysell.com/

Care&Cleaning•  Fingerprints•  Eyelashes•  Dew&Dust•  Cap&Replace•  Resistthetemptationtoclean!•  CleaningSolution:1/3isopropyl

alcohol(99%),2/3distilledwaterand1dropbiodegradabledishsoap

•  Purecottonballs&Q-tips•  Cannedair

OptimizeYourEyepieces•  Filters•  Eyepiecescomethreadedforfilters•  Youguessedit!•  Neutraldensityfilters:moonfilters•  Improvecontrast&preservenight

vision•  0.9density=13%transmission•  Colour-neutralviews•  Oftenthreadedforstacking•  NOTFORSOLARVIEWING!

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SolarFilters•  Block>99%ofSun’slight•  Visual&Photographic•  Sunspots&surfacedetail

LightPollution&SkyGlowFiltersBroadbandfiltersthatblockmostcommonwavelengthsofLPDarkensbackground/IncreasescontrastMostusefulonstarclusters&galaxiesUsefulindarkskiestoo!

PhotographicFilters•  Blue,green,red,orange,yellow•  Usefulforenhancingfeatureson

Jupiter,Saturn,Mars&Moon

NarrowBand&LineFilters•  Oftenreferredtoasnebulafilters•  Enhanceemission&planetary

nebulae

•  Narrowbandfilters

•  Blockallwavelengthsexceptionizedhydrogenanddoublyionizedoxygen

•  UHC

•  Linefilters

•  Blockallwavelengthsexceptforaspecificwavelength

•  OxygenIII(OIII)&Hydrogen-beta(Hβ)

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ObservationalTechniques•  Focusiscritical•  BahtinovMask•  Focuschangesasscopecools•  Focuswillchangewhenanew

eyepieceisinserted:Parfocaleyepieces

•  Focuswillchangewhenyouputinafilter

•  Highmagnificationfocusingisdifficult

•  Electronicfocusers

ObservationalTechniques•  Magnification•  Eyedominance•  Closeoneeye•  Glasses:yesorno?•  Restfacegentlyagainstrubbereye

cup•  Lookstraightdowntheeyepiece•  Rubbereyecupsblockstraylight&

helpcenteryoureye

ObservationalTechniques•  Getcomfortable–sitdown!•  Breathing•  Avertedvision•  Gentlytapthetelescopetosee

dimobjects•  Slowdown&observe!•  Sketchand/ormakenotes•  Experienceallowsyoutoseemore

April3,2020NoviceClassLesson9

DeepSkyObjectsPart1