8.4-m Mirror Blank for Large Binocular Telescope - PowerPoint PPT Presentation

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8.4-m Mirror Blank for Large Binocular Telescope

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Seeing = size of blur. Chromatic Aberration (present in any refracting element) Spherical – PowerPoint PPT presentation

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Title: 8.4-m Mirror Blank for Large Binocular Telescope


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8.4-m Mirror Blank for Large Binocular Telescope
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Polishing one LBT 8.4-m mirror
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TELESCOPES
Palomar 200-in
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The Electromagnetic Spectrum
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Functions of Telescopes
  • Collect more light --- depends on (diam)2
  • Resolve sources better (see more detail)
  • Magnify images

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Telescope Objectives Specially Shaped Main
Optical Element
  • Purpose form an accurate representation of
    original scene at a focus
  • Lens ---gt refracting telescope
  • Mirror ---gt reflecting telescope

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Refraction Bending of Light Rays at a
Glass/Air Interface
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Reflection from a Smooth Surface
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Refracting Telescope
Place detector here
  • Minimum 2 lenses needed for visual use

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  • Image formation (Java demo)

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Reflecting Telescopes
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ReflectingTelescope Designs
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Catadioptric (LensMirror) Design
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Image Inversion in Simple Telescope
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Telescope Performance Characteristics
  • Focal Ratio (f/ number)
  • Magnification ("power")
  • Field of view
  • Light Gathering Power
  • Resolution

17
Focal Ratio
  • f/ number Obj FL / Obj Diam
  • Smaller numbers give more concentrated light in
    focal plane (better for faint extended objects)
    allow shorter exposures with film/electronic
    detectors
  • Higher numbers have better resolution better for
    high magnification (e.g. for planets)

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Magnification
  • Defined to be ratio of apparent angular size of
    image to original angular size (without
    telescope)
  • Mag FL (telescope) / FL (eyepiece)
  • For Celestrons, Mag 2034 mm/FLE (mm)
  • Moderate magnifications (lt150) best

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Field of View
  • True angular diameter -- i.e. as viewed without
    telescope -- of field visible in eyepiece.
  • Usually quoted in degrees or minutes of arc
  • Depends on eyepiece used
  • Is smaller for higher magnification with given
    telescope

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Light Gathering Power
  • Most important attribute of telescope
  • Light collected is proportional to the area of
    the objective, or to Dobj2
  • If the pupil diameter of your eye is 5mm, an 8"
    telescope collects (203/5)2 1600x more light

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AGAIN, JONES' SNEAKY COLLEAGUES AIMED THE
TELESCOPE AT THE SUN
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Table by D. Haworth
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Table by D. Haworth
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Image Quality (Resolution)
  • Design optics to reduce "aberrations" -- e.g.
    chromatic, spherical, etc.
  • Optical figuring to intended shape must be
    better than 1/4 wavelength
  • Larger telescopes better because of diffraction
    of light waves
  • Turbulence in air strongly affects image blur.
    Seeing size of blur.

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Chromatic Aberration (present in any refracting
element)
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Spherical "Aberration"
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Parabola perfect paraxial focus
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Parabola "coma" aberration off-axis
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Longer focal lengths reduce chromatic spherical
aberration (Hevelius, ca. 1650)
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Schmidt-Cassegrain design uses a thin
refractive corrector to eliminate spherical
aberration from a spherically-shaped primary
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8.4-m Mirror Blank for Large Binocular Telescope
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Polishing one LBT 8.4-m mirror
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Diffraction of Light Waves
Ideal case
Real waves
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Seeing Caused by Atmospheric Turbulence
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  • Video of enlarged image of bright star
  • in a large telescope. Image size/motion caused
    by
  • Earths atmosphere.

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Telescope Designs A Multitude
  • Optical design
  • Mounting design
  • Equatorial
  • Altitude-Azimuth

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McCormick 26-in Refractor, Equatorial Mount
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McCormick 26-in Lens (Doublet)
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  • 200-in
  • Dedication (1948)
  • (Largest equatorial mount for
  • optical telescope "horseshoe")

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Astronomer in 200-in Prime Focus Cage
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Celestron CPC-800 Schmidt-Cassegrain (Alt-Az
Mount Shown)
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Galileo Refracting Telescope (1610)
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Reflecting Telescope (Gregory, Newton)
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McCormick Observatory (UVa, 1883)
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  • McCormick 26-in
  • Refractor.
  • Equatorial mount

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200-in Mirror Blank (Pyrex)
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200-inch mirror polishing
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Fringe Benefits of Observing
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Extras
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The telescope (first used 1609) was the critical
invention for astronomy
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