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19 Optical Instruments

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The Camera

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Focusing a Camera

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A digital image is made up of millions of pixels.

Digital Cameras

A CCD chip records the digital image.

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The Human Eye

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Focusing and Accommodation

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Refractive Power

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The refractive power of a lens of focal length f is the inverse of that focal length.

The unit of refractive power is meters-1, or diopters

Eyeglasses are measure in units of diopters, positive or negative

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Hyperopia

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Example for a person who can only focus at 1.5 meters away

Need to create a virtual image at 1.5 meters

3.3m-1 = 3.3 diopters

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Myopia

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To correct nearsightedness, need to create a virtual image of an object that is at infinity that appears to be at 2.0 meters distance, the far point of the person’s vision.

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Apparent Size

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The Magnifier

Largest angular size without a magnifier is

With a magnifier, the angular size is

The magnification is thus

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The Microscope

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Maya performs light microscopy

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The Microscope

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The Telescope

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Color and Dispersion

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Chromatic Aberration

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Resolution and the Wave Nature of Light

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Two objects are resolvable if their angular separation is greater than

Rayleigh’s Criterion

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The Resolution of a Microscope

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Rainbows

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Lens Aberrations: Spherical Aberration

The Hubble space telescope originally suffered from spherical aberration.

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The Very Large Telescope – a four telescope array

“The light beams are combined in the VLTI using a complex system of mirrors in underground tunnels where the light paths must be kept equal to distances less than 1/1000 mm over a hundred metres. With this kind of precision the VLTI can reconstruct images with an angular resolution of milliarcseconds, equivalent to distinguishing the two headlights of a car at the distance of the Moon.”

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Center of the Milky Way

Region near supermassive black hole

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Optical and Electron Micrographs of e. coli

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Scanning electron microscope (SEM)

Beam of electrons, collimated, scanned over specimen in a vacuum

Backscattered electrons are collected, used to determine image

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Creepy nasty bugs shown under SEM

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Transmission electron microscope (TEM)

Passes electrons through the specimen

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Electron Diffraction Images

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Chandra X-Ray ObservatoryFocuses X-Rays by glancing them off hyperbolic surfaces

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Chandra X-Ray Observatory ImageColliding galaxies with supermassive black holes

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Porro prism and roof prism binocular designs

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Stage lightingCompact near-point light source

Computer controlled filters, masks, altazimuth mount

Light 230 watt

Light angle down to 2.25º

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Solar Architecture and Engineering

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Passive solar homes accept or reject sunlight to control climate

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Dimetrodons probably used their “sails” for solar heating

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Cliff dwellings are early solar homes – Made desert life cool

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Atomic force microscopy These are individual atoms

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Near Field Microscopy – Bypassing the Rayleigh Limit

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Reading Quiz1. The units of refractive power are

A. watts.

B. m2.

C. m–1.

D. joules.

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Answer 1. The units of refractive power are

A. watts.

B. m2.

C. m–1.

D. joules.

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Reading Quiz2. Accommodation of the eye refers to its ability to

A. focus on both nearby and distant objects.

B. move in the eye socket to look in different directions.

C. see on both the brightest days and in the dimmest light.

D. see both in air and while under water.

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Answer 2. Accommodation of the eye refers to its ability to

A. focus on both nearby and distant objects.

B. move in the eye socket to look in different directions.

C. see on both the brightest days and in the dimmest light.

D. see both in air and while under water.

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Reading Quiz3. The magnification of a microscope is increased when

A. the focal length of the objective lens is increased.

B. the focal length of the objective lens is decreased.

C. the focal length of the eyepiece is increased.

D. the distance between the objective lens and eyepiece is decreased.

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Answer 3. The magnification of a microscope is increased when

A. the focal length of the objective lens is increased.

B. the focal length of the objective lens is decreased.

C. the focal length of the eyepiece is increased.

D. the distance between the objective lens and eyepiece is decreased.

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4. The fundamental resolution of an optical instrument is set by

A. the accuracy to which lenses can be polished.

B. the fact that white light is composed of all visible colors.

C. the fact that all types of glass have nearly the same index of refraction.

D. the wave nature of light.

Reading Quiz

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Answer 4. The fundamental resolution of an optical instrument is set by

A. the accuracy to which lenses can be polished.

B. the fact that white light is composed of all visible colors.

C. the fact that all types of glass have nearly the same index of refraction.

D. the wave nature of light.

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