Chapter 24. Optical Instruments From eyeglasses to · PDF fileChapter 24. Optical Instruments...

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Transcript of Chapter 24. Optical Instruments From eyeglasses to · PDF fileChapter 24. Optical Instruments...

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    Copyright 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.

    Chapter 24. Optical Instruments

    From eyeglasses to

    microscopes and telescopes,

    our everyday world is filled

    with optical instruments,

    devices that aid our senses

    by using lenses and mirrors

    to form images we wouldnt

    be able to see, or see as well,

    with our eyes alone.

    Chapter Goal: To

    understand some common

    optical instruments and their

    limitations. 2Copyright 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.

    Topics:

    Lenses in Combination

    The Camera

    Vision

    Optical Systems that Magnify

    The Resolution of Optical Instruments

    Chapter 24. Optical Instruments

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    Chapter 24. Reading Quizzes

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    With what unit is lens power measured?

    A. Biopter

    B. Diopter

    C. Watt

    D. Rayleigh

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    Copyright 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.

    With what unit is lens power measured?

    A. Biopter

    B. Diopter

    C. Watt

    D. Rayleigh

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    Accommodation of the eye refers to

    its ability to

    A. rotate in the eye socket to look in

    different directions.

    B. focus on both nearby and distant objects.

    C. see in both very bright and very dim light.

    D. see both in air and while underwater.

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    Accommodation of the eye refers to

    its ability to

    A. rotate in the eye socket to look in

    different directions.

    B. focus on both nearby and distant

    objects.

    C. see in both very bright and very dim light.

    D. see both in air and while underwater.

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    The magnification of a simple magnifier

    is increased if

    A. the focal length of the lens is increased.

    B. the focal length of the lens is decreased.

    C. the diameter of the lens is increased.

    D. the diameter of the lens is decreased.

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    The magnification of a simple magnifier

    is increased if

    A. the focal length of the lens is increased.

    B. the focal length of the lens is decreased.

    C. the diameter of the lens is increased.

    D. the diameter of the lens is decreased.

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    The fundamental resolution of

    a lens or telescope is

    determined by

    A. the parallax theorem.

    B. the numerical aperture of the lens.

    C. Rayleighs criterion.

    D. the lens makers principle.

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    The fundamental resolution of

    a lens or telescope is

    determined by

    A. the parallax theorem.

    B. the numerical aperture of the lens.

    C. Rayleighs criterion.

    D. the lens makers principle.

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    Chapter 24. Basic Content and Examples

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    Lenses in Combination

    The analysis of multi-lens systems requires only one new

    rule: The image of the first lens acts as the object for the

    second lens.

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    The Camera

    A camera takes a picture by

    using a lens to form a real, inverted

    image on a light-sensitive detector

    in a light-tight box.

    We can model a combination lens

    as a single lens with an effective

    focal length (usually called simply

    the focal length)

    A zoom lens changes the effective

    focal length by varying the spacing

    between the converging lens and

    the diverging lens.

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    EXAMPLE 24.2 Focusing a camera

    QUESTION:

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    EXAMPLE 24.2 Focusing a camera

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    EXAMPLE 24.2 Focusing a camera

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    EXAMPLE 24.2 Focusing a camera

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    Zoom Lenses

    When cameras focus on objects that are more that 10 focal

    lengths away (roughly s > 20 cm for a typical digital

    camera), the object is essentially at infinity and s' f.

    The lateral magnification of the image is

    The magnification is much less than 1, because s >> f, so

    the image on the detector is much smaller than the object

    itself.

    More important, the size of the image is directly

    proportional to the focal length of the lens.

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    Controlling the Exposure

    The amount of light passing through the lens is controlled

    by an adjustable aperture, also called an iris because it

    functions much like the iris of your eye.

    The aperture sets the effective diameter D of the lens.

    By long tradition, the light-gathering ability of a lens is

    specified by its f-number, defined as

    The light intensity on the detector is related to the

    lenss f-number by

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    Vision The human eye is roughly spherical, about 2.4 cm in

    diameter.

    The transparent cornea and the lens are the eyes refractive elements.

    The eye is filled with a clear, jellylike fluid called the aqueous humor and the vitreous humor.

    The indices of refraction of the aqueous and vitreous humors are 1.34, only slightly different from water.

    The lens has an average index of 1.44.

    The pupil, a variable-diameter aperture in the iris, automatically opens and closes to control the light intensity.

    The f-number varies from roughly f/3 to f/16, very similar to a camera.

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    Focusing and Accommodation

    The eye focuses by changing the focal length of the lens

    by using the ciliary muscles to change the curvature of the

    lens surface.

    Tensing the ciliary muscles causes accommodation,

    which decreases the lenss radius of curvature and thus

    decreases its focal length.

    The farthest distance at which a relaxed eye can focus is

    called the eyes far point (FP). The far point of a normal

    eye is infinity; that is, the eye can focus on objects

    extremely far away.

    The closest distance at which an eye can focus, using

    maximum accommodation, is the eyes near point (NP).

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    EXAMPLE 24.4 Correcting hyperopia

    QUESTION:

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    EXAMPLE 24.4 Correcting hyperopia

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    EXAMPLE 24.4 Correcting hyperopia

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    EXAMPLE 24.4 Correcting hyperopia

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    EXAMPLE 24.5 Correcting myopia

    QUESTION:

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    EXAMPLE 24.5 Correcting myopia

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    EXAMPLE 24.5 Correcting myopia

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    EXAMPLE 24.5 Correcting myopia

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    The Microscope

    A specimen to be observed is placed on the stage of a

    microscope, directly beneath the objective, a converging

    lens with a relatively short focal length.

    The objective creates a magnified real image that is

    further enlarged by the eyepiece.

    The lateral magnification of the objective is

    Together, the objective and eyepiece produce a total

    angular magnification

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