Eyepieces

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Eyepieces

• The rest of the scope

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First Some Credits

• Much of the material for this presentation is
  from the TeleVue web site
• Televue Products are featured in this presentation

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Eyepieces The Other Part Of The Optics
Al Nagler
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Some Important Terms

• Focuser Type
• Barrel Size
• Magnification
• Field of View
• Eye Relief
• Eyepiece Type
• Seeing

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Focuser

• Eyepieces focus by being moved toward and away
  from Primary
• Some Focuser Types
• Helical
• Rack and Pinion
• Crayford
• Electronic

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Barrel Size

• Defines size of hole in the focuser is
• Most are 1.25
• High End Eyepieces are 2
• Run from any scope with .96

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Magnification

• Defines How much something is enlarged
• Prominent in Adverteasing
• Almost always wrong
• Any scope that adverts mag is suspicious
• Field of View more useful

10 x
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How Eyepiece Determines Magnification

• Magnification Focal Length / Eyepiece
• But
• Laws of Physics Limit
• 60x per inch (less for crummy optics)
• gt 300x rare due to atmosphere

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Apparent Field Of View

• Property of technology of Eyepiece
• Used to Determine True FOV

Panoptic 68
Nagler 82
Plössls 50
Radian 60
TeleVue Eyepieces Other Manufactures have
competing brands
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True Field of View

• True field of view Apparent field of view
  
• 
  Magnification
• This Is The Useful Measurement
• Says What Eyepiece Will Do With This Scope

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Eye ReliefHow Far Eye Can Be From Eyepiece

• Glass Wearers cant get as close
• High E.R. Annoying if you dont wear glasses
• Adjustable pupil guide for non wearers
• Reduces Looking through Keyhole effect

http//www.birdwatching.com/optics/eye_relief.html
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Glasses and Eyepieces

• Do you have astigmatism?
• Amount of Cylinder in Prescription
• With Small Astigmatism Eyeglasses not needed
• Large Cylinder will benefit from eyeglasses
• TeleVue DIOPTRX

Astigmatism
Slightly out of focus
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Eyepiece Technologies

• Plossl Low Cost
• Nagler Quality Benchmark, Highest Cost
• Radian High Eye Relief
• Panoptic Wide Field, lower cost than Nagler
• Also Good
• Pentax XL, Burgess
• Varies
• Orion, Meade, etc

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Some Examples of FOV

• Three Scopes
• TV-76 FL 460mm - Wide Field Refractor
• 8 f/6 Dob 1200 mm - Common Beginner Scope
• 15 f/5 Dob 1900 mm High End Scope

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Applying TFOV Coat Hanger Cluster (CR399)
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Applying TFOV - moon
Using 8 f/6 Scope
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Applying TFOV M 57
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Applying TFOV M81/82
15 f/5 Plettstone Dob
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Things that can go wrong Eyepiece Technology

• Field Curvature
• Edges not in focus
• Coma
• Comet shaped stars

One (or both) of these problems affect all
Plossls, Orthos, etc Reduces Usable FOV
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Crummy Optics

• Distortion
• Straight objects looked curved
• Astigmatism
• Color
• TeleVue is highest quality
• Some competitors offer similar quality at much
  lower price

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Seeing

• How much the atmosphere is distorting image
• See weather presentation

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How High is Too High?
Low power Bands visible
High Power magnifies Noise
More Magnification Makes Poor Seeing Worse!
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Can More Power Let You See Dimmer?

• Maybe - Depends on Your Eyes
• Is concentrated light better?
• Low Power
• Each Rod exposed to more light
• Is Exposing More Rods better?
• Hold Still
• Jiggle Scope
• Somewhat darkens background
• Averted Vision in either case

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Which Eyepiece to use?

• Depends on which scope and object
• Most People migrate to better eyepieces
• I tend to operate at 100x with a 10 scope