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Observing equipmentObserving equipment

Types of observing equipmentTypes of observing equipmentwe shall coverwe shall cover

EyesEyesBinocularsBinocularsTelescopesTelescopesRefractorsRefractorsReflectorsReflectorsMountsMountsEyepiecesEyepiecesFiltersFilters

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Using your eyesUsing your eyes

Rods Rods -- night visionnight visionCones Cones -- colour visioncolour vision

OpticsOptics

ApertureApertureSize of primary lensSize of primary lensDetermines resolutionDetermines resolution

MagnificationMagnificationFocal length divided by Focal length divided by EP focal lengthEP focal lengthLess importantLess important

Field of viewField of vieweyepiece field of view eyepiece field of view divided by magnificationdivided by magnification

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Optics (continued)Optics (continued)

Optical aberrationsOptical aberrationsSpherical aberrationSpherical aberrationChromatic aberrationChromatic aberrationComaComa

Diffraction imagesDiffraction imageswave nature of light determines thiswave nature of light determines thiseffect of secondary obstructioneffect of secondary obstruction

CoatingsCoatings

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BinocularsBinoculars

Magnification x apertureMagnification x apertureExit pupilExit pupilField of viewField of viewPrismsPrismsBak4Bak4Bak7Bak7MountsMounts

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RefractorsRefractors

Pluses and minusesPluses and minusesDoubletDoublet

AchromatAchromatApochromatApochromatStar diagonalStar diagonal

ReflectorsReflectors

Newtonian telescopeNewtonian telescopepluses and minusespluses and minusesbrief historybrief historywhy a parabola?why a parabola?

Maksutov NewtonianMaksutov Newtonianpluses and minusespluses and minuseswhy a meniscus lens?why a meniscus lens?

Classical CassegrainClassical Cassegrainpluses and minusespluses and minusesBrief historyBrief history

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CatadioptricsCatadioptrics

Maksutov CassegrainMaksutov Cassegrainpluses and minusespluses and minuses

CatadioptricsCatadioptrics

Schmidt CassegrainSchmidt Cassegrainpluses and minusespluses and minuseswhy so succesful?why so succesful?

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MountsMounts

AltAlt--azazup and downup and downside to sideside to sidecheapcheapdoesn't follow the skydoesn't follow the sky

DobsonianDobsonian

Mounts (continued)Mounts (continued)

EquatorialEquatorialtracks the skytracks the skyone bearing aligned one bearing aligned with earth's polar axiswith earth's polar axisGermanGermanfork mountfork mount

Equatorial platform for Equatorial platform for an altan alt--az mountaz mount

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Eyepieces 101Eyepieces 101

MagnificationMagnificationField of viewField of viewEye reliefEye reliefExit pupilExit pupil

effM =

MFVFV e

a =

MDExP =

FfExP e=

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10

Spherical aberrationSpherical aberration

Field distortionField distortion

1

2

1

2

PP

hh

≠

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ComaComa

Due to light beams not being parallel to Due to light beams not being parallel to the main optical axis of a telescopethe main optical axis of a telescope

Short focus NewtoniansShort focus Newtonians

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13

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AstigmatismAstigmatism

Chromatic aberrationChromatic aberration

Often fixed by using different sorts of glassin combination

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Other optical characteristicsOther optical characteristics

SharpnessSharpnessHard to measure objectivelyHard to measure objectively

ContrastContrastTypically less contrast with more lens Typically less contrast with more lens elementselements

GhostingGhostingOften due to poor coatingsOften due to poor coatings

Kidney beanKidney bean

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HuygensHuygens

Christian HuygensChristian Huygens17031703

Spherical aberrationSpherical aberrationChromatic aberrationChromatic aberrationNarrow apparent fieldNarrow apparent fieldOK with large F ratioOK with large F ratio

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RamsdenRamsden

Christian Christian RamsdenRamsden17831783

Spherical aberrationSpherical aberrationChromatic aberrationChromatic aberrationNarrow apparent fieldNarrow apparent fieldOK with large F ratioOK with large F ratioSmall improvementSmall improvement

KellnerKellner

Carl Carl KellnerKellner18461846

AchromaticAchromaticCrown & flint glassCrown & flint glass

Fewer aberrationsFewer aberrations4040--5050ºº apparent fieldapparent fieldInternal reflectionsInternal reflections

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OrthoscopicOrthoscopic

Ernst Ernst AbbAbbéé18801880

ApochromaticApochromaticFewer aberrationsFewer aberrationsFairly flat fieldFairly flat field4040--5050ºº apparent fieldapparent fieldSweet spotSweet spot

ErfleErfle

MilitaryMilitary19171917

ApochromaticApochromaticFewer aberrationsFewer aberrationsEdge distortionEdge distortion

AstigmatismAstigmatism

6060--7070ºº apparent fieldapparent fieldGood for low power, Good for low power, wide angleswide angles

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PlPlöösslssl

G.S. G.S. PlösslPlössl18601860

Twin doubletsTwin doubletsFew aberrationsFew aberrations5050ºº apparent fieldapparent fieldGood for a wide Good for a wide variety of purposesvariety of purposes

NaglerNagler

Al Al NaglerNagler~1980~1980

Multiple elementsMultiple elementsFew aberrationsFew aberrations>80>80ºº apparent fieldapparent fieldSmall eye reliefSmall eye relief

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Which eyepiece?Which eyepiece?

Depends on target and telescopeDepends on target and telescopeCombination of telescope and eyepiece Combination of telescope and eyepiece determines exit pupildetermines exit pupilOptimal exit pupils for different objectsOptimal exit pupils for different objects

MDExP =

FfExP e=

FExPfe *=

Optimal eyepiecesOptimal eyepieces

0.50.5Close double starsClose double stars

0.80.8Optimal planet detailOptimal planet detail

22Moon, small globs, double starsMoon, small globs, double stars

33DSOs (nebulae, clusters, etc.)DSOs (nebulae, clusters, etc.)

55--66Wide field (older person)Wide field (older person)

77Wide field (young person)Wide field (young person)

Exit pupilExit pupilTargetTarget

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FiltersFilters

Nebula filterNebula filterOIII filterOIII filterLight pollution reduction filtersLight pollution reduction filtersPlanetary filtersPlanetary filtersSolar filterSolar filterH H αα filterfilter