Optical Instruments

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  Optics

  An Introduction

  • Sarhan M. Musa(Author)
  • 2020(Publication Date)
  • Mercury Learning and Information

    (Publisher)

  CHAPTER 5

  Optical Instruments

  Chapter Outline

  5.0

  Introduction

  5.1

  The Eye

  5.2

  The Compound Microscope

  5.3

  Microscope Objective

  5.4

  Dark Field Illumination

  5.5

  Telescopes

  5.6

  The Astronomical Refracting Telescope

  5.7

  Oculars or Eyepieces

  5.8

  The Spectrometer

  5.9

  Exercises

  5.0 INTRODUCTION

  Optical Instruments may be conveniently divided into two general classes: (a) the image forming instruments, and (b) the analyzing instruments. Telescopes, microscopes, prismatic binoculars, and so on come under the first class, because these instruments are employed to examine objects by forming their images, much magnified in size as compared with those formed by the unaided eye. Prism-spectrometers, grating spectrometers, and interferometers belong to the second class, because these instruments are primarily employed to discover what wavelengths are present in a given beam of light, incident on the instrument, thereby analyzing the given light. The function of most of the image-forming instruments is to enable us to see better, and consequently the eye should be regarded as an essential part of every visual optical instrument. Before describing the optical system of any visual instrument, therefore, it is best to describe the essential parts constituting the eye and discuss its image-forming properties, limiting our discussion only to the physical principles involved in the process of image formation.

  5.1 THE EYE

  The essential parts of the human eye, considered as an optical instrument, are illustrated by the sectional Figure 5.1 of the eye.

  FIGURE 5.1. The eye.

  The eye is roughly spherical in shape, the front part being slightly more curved, and is covered with a tough transparent membrane C, called the cornea. Behind the cornea is a weak salt solution known as the aqueous humor A, backed by a crystalline lens L of varying optical density. The lens is of fibrous jelly, harder at the center and then gradually becoming softer toward the surface, the refractive index varying between 1.38 and 1.41. It is held in position by the suspensory ligaments I through which it is connected to the ciliary muscle M, which is spread all around the lens. The remainder of the eyeball is filled with a thin, transparent jelly consisting largely of viscous liquid called the vitreous humor V. The refractive index of both the vitreous humor and the aqueous humor is 1.336. The cornea and the crystalline lens essentially constitute a compound convergent lens system which forms on sensitive nerve fibers and cells, called the retina R, inverted images of objects, situated near or far away in front of the eye. The nerve fibers constituting the retina are in fact the branches of the optic nerve O and terminate in minute structures called rods and cones. In and about them circulates a bluish liquid known as visual purple. The optic nerve is connected to the mind, and thus the image formed on the retina is transmitted via the optic nerve to the mind. The point at which optic nerve enters the eye is called the blind spot B

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  Light and Optics

  Principles and Practices

  • Abdul Al-Azzawi(Author)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  14 Optical Instruments for Viewing Applications 14.1 INTRODUCTION

  The previous chapters presented the principles of image formation by optical components, such as mirrors and lenses. This chapter presents the use of these optical components in building common Optical Instruments. Such Optical Instruments include the eye, camera, projector, microscope, telescope, and binoculars, which are used for different vision enhancement applications. These Optical Instruments help people to perform ordinary and sophisticated tasks associated with vision, magnification, and image formation. The ray diagram method is used in image formation in these devices. Image formation by the mirrors, lenses, lenses combinations, and prisms is discussed in detail in the previous chapters. There are many optical devices and instruments using basic optical components that are covered in other chapters.

  This chapter includes an experiment involving the operation, image formation, functionality, disassembly, and reassembly of the optical components of an optical viewing instrument. 14.2 Optical Instruments

  There is a wide variety of optical devices, instruments, and systems that use mirrors and lenses, for example: cameras, microscopes, projectors, and telescopes. There are also Optical Instruments that use prisms, gratings, and fibre optics, along with one type of lens or mirror. These instruments will be described later in the optics and optical fibre sections of this book. Such optical components are commonly used in manufacturing optical fibre devices, which are used in building communication systems, medical instruments, scanning and imaging processors, optical spectrum analysers, etc.

  14.3 THE CAMERA

  Cameras are among the most common of Optical Instruments. The camera shown in Figure 14.1 is a simple optical instrument. Figure 14.2

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  eBook - ePub

  Optics For Dummies

  • Galen C. Duree, Jr.(Authors)
  • 2011(Publication Date)
  • For Dummies

    (Publisher)

  Part IV Optical Instrumentation: Putting Light to Practical Use

  In this part . . .

  T

  his part looks at how you can use the basic processes of manipulating light to make practical devices — tools that do something that you want. In this part, you see how eyeglasses correct for common vision problems and how other devices change the properties of images so that you can see objects that are far away or very tiny. The part also covers useful ways to produce light, including the development of a very unique light source, the laser. Finally, I discuss the basic ideas behind light guides and give you the scoop on using a fiber-optic link to send information.

  Passage contains an image

  Chapter 13 Lens Systems: Looking at Things the Way You Want to See Them In This Chapter

  Discovering some important optical properties of the human eye

  Understanding common vision problems and how lens systems correct them

  Reaching beyond the eye’s natural capabilities with optical devices

  S

  ight is the primary physical sensor for human beings. Because sight involves light, optical systems have for many centuries played a very important part in improving the way humans can experience life. Although some basic devices (such as lenses and mirrors) and manipulation methods can affect what light does with images, they provide only a limited capability to do more than what the human eye can do alone. However, combining these elements in just the right way creates possibilities that far exceed the eye’s limits.

  In this chapter, I describe some of the optical characteristics of your primary optical system — your eyes. Because some people’s eyes function differently in some situations, I present the most common basic problems with the human eye and explain how an eye doctor can help correct some of these problems. Finally, I discuss some optical arrangements called lens systems that can enhance sight.

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  College Physics

  • Paul Peter Urone, Roger Hinrichs(Authors)
  • 2012(Publication Date)
  • Openstax

    (Publisher)

  Intricate images help us understand nature and are invaluable for developing techniques and technologies in order to improve the quality of life. The image of a red blood cell that almost fills the cross-sectional area of a tiny capillary makes us wonder how blood makes it through and not get stuck. We are able to see bacteria and viruses and understand their structure. It is the knowledge of physics that provides fundamental understanding and models required to develop new techniques and instruments. Therefore, physics is called an enabling science—a science that enables development and advancement in other areas. It is through optics and imaging that physics enables advancement in major areas of biosciences. This chapter illustrates the enabling nature of physics through an understanding of how a human eye is able to see and how we are able to use Optical Instruments to see beyond what is possible with the naked eye. It is convenient to categorize these instruments on the basis of geometric optics (see Geometric Optics) and wave optics (see Wave Optics). 26.1 Physics of the Eye The eye is perhaps the most interesting of all Optical Instruments. The eye is remarkable in how it forms images and in the richness of detail and color it can detect. However, our eyes commonly need some correction, to reach what is called “normal” vision, but should be called ideal rather than normal. Image formation by our eyes and common vision correction are easy to analyze with the optics discussed in Geometric Optics. Figure 26.2 shows the basic anatomy of the eye. The cornea and lens form a system that, to a good approximation, acts as a single thin lens. For clear vision, a real image must be projected onto the light-sensitive retina, which lies at a fixed distance from the lens. The lens of the eye adjusts its power to produce an image on the retina for objects at different distances.

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  Principles of Optics

  Electromagnetic Theory of Propagation, Interference and Diffraction of Light

  • Max Born, Emil Wolf(Authors)
  • 2013(Publication Date)
  • Pergamon

    (Publisher)

  C H A P T E R V I I M A G E -F O R M I N G I N S T R U M E N T S T H E three preceding chapters give an account of the geometrical theory of optical imaging, using for the main part the predictions of Gaussian optics and of the Seidel theory. An outstanding instance of the invaluable service rendered by this branch of optics lies in its ability to present the working principles of Optical Instruments in an easily visualized form. Although the quality of optical systems cannot be estimated by means of Gaussian theory alone, the purpose served by the separate optical elements can be indicated in this way, so that a simple, though somewhat approximate, picture of the action of the system can often be obtained without entering into the full intricacy of the techniques of optical design. The development of Optical Instruments in the past has proceeded just as fast as technical difficulties have been overcome. It is hardly possible to give a step-by-step account of the design of optical systems, for two reasons. Firstly, the limitations of a given arrangement are not indicated by the predictions of the simple theory; in particular cases this needs to be supplemented by a fuller analysis often involving tedious calculations. Secondly, difficulties of a practical nature may prevent an otherwise praiseworthy arrangement from being used. It is not intended in this account to discuss the theoretical and practical limitations in individual cases ; only the basic principles underlying the arrangement of some of the more important Optical Instruments will be given, in order to provide a framework for some of the later chapters which deal with the more detailed theories of optical image formation.* 6.1 T H E E Y E Perhaps the simplest of Optical Instruments is that consisting of a single convergent lens forming a real image of an object upon a light-sensitive surface. Examples of such an optical system are found in the photographic camera and in the eye (Fig. 6.1).

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