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20-03-01
1
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