Title: 8.4-m Mirror Blank for Large Binocular Telescope
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28.4-m Mirror Blank for Large Binocular Telescope
3Polishing one LBT 8.4-m mirror
4TELESCOPES
Palomar 200-in
5The Electromagnetic Spectrum
6Functions of Telescopes
- Collect more light --- depends on (diam)2
- Resolve sources better (see more detail)
- Magnify images
7Telescope 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
8Refraction Bending of Light Rays at a
Glass/Air Interface
9Reflection from a Smooth Surface
10Refracting Telescope
Place detector here
- Minimum 2 lenses needed for visual use
11- Image formation (Java demo)
12Reflecting Telescopes
13ReflectingTelescope Designs
14Catadioptric (LensMirror) Design
15Image Inversion in Simple Telescope
16Telescope Performance Characteristics
- Focal Ratio (f/ number)
- Magnification ("power")
- Field of view
- Light Gathering Power
- Resolution
17Focal 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)
18Magnification
- 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
19Field 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
20Light 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
21AGAIN, JONES' SNEAKY COLLEAGUES AIMED THE
TELESCOPE AT THE SUN
22Table by D. Haworth
23Table by D. Haworth
24Image 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.
25Chromatic Aberration (present in any refracting
element)
26Spherical "Aberration"
27Parabola perfect paraxial focus
28Parabola "coma" aberration off-axis
29Longer focal lengths reduce chromatic spherical
aberration (Hevelius, ca. 1650)
30Schmidt-Cassegrain design uses a thin
refractive corrector to eliminate spherical
aberration from a spherically-shaped primary
318.4-m Mirror Blank for Large Binocular Telescope
32Polishing one LBT 8.4-m mirror
33Diffraction of Light Waves
Ideal case
Real waves
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35Seeing Caused by Atmospheric Turbulence
36- Video of enlarged image of bright star
- in a large telescope. Image size/motion caused
by - Earths atmosphere.
37Telescope Designs A Multitude
- Optical design
- Mounting design
- Equatorial
- Altitude-Azimuth
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40McCormick 26-in Refractor, Equatorial Mount
41McCormick 26-in Lens (Doublet)
42- 200-in
- Dedication (1948)
- (Largest equatorial mount for
- optical telescope "horseshoe")
43Astronomer in 200-in Prime Focus Cage
44Celestron CPC-800 Schmidt-Cassegrain (Alt-Az
Mount Shown)
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49Galileo Refracting Telescope (1610)
50Reflecting Telescope (Gregory, Newton)
51McCormick Observatory (UVa, 1883)
52- McCormick 26-in
- Refractor.
- Equatorial mount
53200-in Mirror Blank (Pyrex)
54200-inch mirror polishing
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56Fringe Benefits of Observing
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65Extras
66The telescope (first used 1609) was the critical
invention for astronomy
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