Figure 19.17 A telescope enlarges the angular size of a distant object. Notice that the arrangement of lenses for the telescope in Figure 19.17 results in an inverted image. Most astronomical telescopes are arranged like this. It really does not matter to an Astronomer if she is viewing a star cluster upside down or right side up. However, for viewing something on Earth, a terrestrial telescope needs to have a final upright image. Binoculars often do this by reflections with prisms that correctly orient the image to be upright as well as shortening the distance between the objective and eyepiece lenses. Figure 19.18 shows another way of obtaining an upright image. Opera glasses or field glasses use this arrangement of lenses. In this arrangement, the eyepiece is a diverging lens and intercepts the light before the real image of the objective lens is produced. This arrangement is also beneficial because it shortens the distance between the lenses. Just as with an astronomical telescope, the objective lens forms a real image. While this real image is small, it is nearby so observation is far easier than for the original object. A diverging lens is now used as an eyepiece and is positioned so its focal point coincides with the real image. This produces an upright virtual image at infinity. Figure 19.19 "Opera glasses" or "field glasses" use a negative or diverging lens in the eyepiece to produce an upright image. The magnification of a telescope is given by M = fobj / feye where fobj is the focal length of the objective lens and feye is the focal length of the eyepiece. That means a large magnification results from a long focal length objective lens and a short focal length eyepiece. All lenses suffer aberrations of various kinds. chromatic aberration is the problem that glass bends or refracts light of different colors different amounts. This means that light of one color is focused as a slightly different position than light of another color. One way to eliminate chromatic aberration is to substitute a mirror for the objective lens. Such a telescope was first invented by Sir Isaac Newton and is illustrated in Figures 19.20 and 19.21. A large spherical or parabolic mirror focuses the light the same as the objective lens we have just studied. A small mirror is placed in front of this objective mirror and diverts the light to one side where the image may be viewed with an eyepiece. A variation of this, called a Cassegrainian telescope, is also shown in the figure. There, a small mirror reflects the light through a hole in the objective mirror. Almost all large astronomical telescopes use mirrors, such as the one in Figure 19.22. Such reflecting telescopes have several advantages over refracting telescopes-lack of chromatic aberration, only one surface to grind and polish, and the weight of a large mirror can be supported along its back (the weight of a large lens can be supported only at its edges and this will cause a lens to "sag"). Figure 19.21 Light of all wavelengths is focused the same in a reflecting telescope like this one invented by Sir Isaac Newton. Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors.

量子效率

A telescope is used for viewing distant objects. In some sense a telescope is designed like the microscope we have just discussed. A front, objective lens produces a real image that is then viewed by an eyepiece as a simple magnifier. This is illustrated in Figure 19.17. The real image produced by the objective lens is small but it is nearby and can be observed with the eyepiece. Figure 19.17 A telescope enlarges the angular size of a distant object. Notice that the arrangement of lenses for the telescope in Figure 19.17 results in an inverted image. Most astronomical telescopes are arranged like this. It really does not matter to an Astronomer if she is viewing a star cluster upside down or right side up. However, for viewing something on Earth, a terrestrial telescope needs to have a final upright image. Binoculars often do this by reflections with prisms that correctly orient the image to be upright as well as shortening the distance between the objective and eyepiece lenses. Figure 19.18 shows another way of obtaining an upright image. Opera glasses or field glasses use this arrangement of lenses. In this arrangement, the eyepiece is a diverging lens and intercepts the light before the real image of the objective lens is produced. This arrangement is also beneficial because it shortens the distance between the lenses. Just as with an astronomical telescope, the objective lens forms a real image. While this real image is small, it is nearby so observation is far easier than for the original object. A diverging lens is now used as an eyepiece and is positioned so its focal point coincides with the real image. This produces an upright virtual image at infinity. Figure 19.19 "Opera glasses" or "field glasses" use a negative or diverging lens in the eyepiece to produce an upright image. The magnification of a telescope is given by M = fobj / feye where fobj is the focal length of the objective lens and feye is the focal length of the eyepiece. That means a large magnification results from a long focal length objective lens and a short focal length eyepiece. All lenses suffer aberrations of various kinds. chromatic aberration is the problem that glass bends or refracts light of different colors different amounts. This means that light of one color is focused as a slightly different position than light of another color. One way to eliminate chromatic aberration is to substitute a mirror for the objective lens. Such a telescope was first invented by Sir Isaac Newton and is illustrated in Figures 19.20 and 19.21. A large spherical or parabolic mirror focuses the light the same as the objective lens we have just studied. A small mirror is placed in front of this objective mirror and diverts the light to one side where the image may be viewed with an eyepiece. A variation of this, called a Cassegrainian telescope, is also shown in the figure. There, a small mirror reflects the light through a hole in the objective mirror. Almost all large astronomical telescopes use mirrors, such as the one in Figure 19.22. Such reflecting telescopes have several advantages over refracting telescopes-lack of chromatic aberration, only one surface to grind and polish, and the weight of a large mirror can be supported along its back (the weight of a large lens can be supported only at its edges and this will cause a lens to "sag"). Figure 19.21 Light of all wavelengths is focused the same in a reflecting telescope like this one invented by Sir Isaac Newton. Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors. [Prev Section] [Next Section] [Table of Contents] [Chapter Contents]

Figure 19.17 A telescope enlarges the angular size of a distant object. Notice that the arrangement of lenses for the telescope in Figure 19.17 results in an inverted image. Most astronomical telescopes are arranged like this. It really does not matter to an Astronomer if she is viewing a star cluster upside down or right side up. However, for viewing something on Earth, a terrestrial telescope needs to have a final upright image. Binoculars often do this by reflections with prisms that correctly orient the image to be upright as well as shortening the distance between the objective and eyepiece lenses. Figure 19.18 shows another way of obtaining an upright image. Opera glasses or field glasses use this arrangement of lenses. In this arrangement, the eyepiece is a diverging lens and intercepts the light before the real image of the objective lens is produced. This arrangement is also beneficial because it shortens the distance between the lenses. Just as with an astronomical telescope, the objective lens forms a real image. While this real image is small, it is nearby so observation is far easier than for the original object. A diverging lens is now used as an eyepiece and is positioned so its focal point coincides with the real image. This produces an upright virtual image at infinity. Figure 19.19 "Opera glasses" or "field glasses" use a negative or diverging lens in the eyepiece to produce an upright image. The magnification of a telescope is given by M = fobj / feye where fobj is the focal length of the objective lens and feye is the focal length of the eyepiece. That means a large magnification results from a long focal length objective lens and a short focal length eyepiece. All lenses suffer aberrations of various kinds. chromatic aberration is the problem that glass bends or refracts light of different colors different amounts. This means that light of one color is focused as a slightly different position than light of another color. One way to eliminate chromatic aberration is to substitute a mirror for the objective lens. Such a telescope was first invented by Sir Isaac Newton and is illustrated in Figures 19.20 and 19.21. A large spherical or parabolic mirror focuses the light the same as the objective lens we have just studied. A small mirror is placed in front of this objective mirror and diverts the light to one side where the image may be viewed with an eyepiece. A variation of this, called a Cassegrainian telescope, is also shown in the figure. There, a small mirror reflects the light through a hole in the objective mirror. Almost all large astronomical telescopes use mirrors, such as the one in Figure 19.22. Such reflecting telescopes have several advantages over refracting telescopes-lack of chromatic aberration, only one surface to grind and polish, and the weight of a large mirror can be supported along its back (the weight of a large lens can be supported only at its edges and this will cause a lens to "sag"). Figure 19.21 Light of all wavelengths is focused the same in a reflecting telescope like this one invented by Sir Isaac Newton. Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors.

Internalquantum efficiency

Figure 19.18 shows another way of obtaining an upright image. Opera glasses or field glasses use this arrangement of lenses. In this arrangement, the eyepiece is a diverging lens and intercepts the light before the real image of the objective lens is produced. This arrangement is also beneficial because it shortens the distance between the lenses. Just as with an astronomical telescope, the objective lens forms a real image. While this real image is small, it is nearby so observation is far easier than for the original object. A diverging lens is now used as an eyepiece and is positioned so its focal point coincides with the real image. This produces an upright virtual image at infinity. Figure 19.19 "Opera glasses" or "field glasses" use a negative or diverging lens in the eyepiece to produce an upright image. The magnification of a telescope is given by M = fobj / feye where fobj is the focal length of the objective lens and feye is the focal length of the eyepiece. That means a large magnification results from a long focal length objective lens and a short focal length eyepiece. All lenses suffer aberrations of various kinds. chromatic aberration is the problem that glass bends or refracts light of different colors different amounts. This means that light of one color is focused as a slightly different position than light of another color. One way to eliminate chromatic aberration is to substitute a mirror for the objective lens. Such a telescope was first invented by Sir Isaac Newton and is illustrated in Figures 19.20 and 19.21. A large spherical or parabolic mirror focuses the light the same as the objective lens we have just studied. A small mirror is placed in front of this objective mirror and diverts the light to one side where the image may be viewed with an eyepiece. A variation of this, called a Cassegrainian telescope, is also shown in the figure. There, a small mirror reflects the light through a hole in the objective mirror. Almost all large astronomical telescopes use mirrors, such as the one in Figure 19.22. Such reflecting telescopes have several advantages over refracting telescopes-lack of chromatic aberration, only one surface to grind and polish, and the weight of a large mirror can be supported along its back (the weight of a large lens can be supported only at its edges and this will cause a lens to "sag"). Figure 19.21 Light of all wavelengths is focused the same in a reflecting telescope like this one invented by Sir Isaac Newton. Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors.

The magnification of a telescope is given by M = fobj / feye where fobj is the focal length of the objective lens and feye is the focal length of the eyepiece. That means a large magnification results from a long focal length objective lens and a short focal length eyepiece. All lenses suffer aberrations of various kinds. chromatic aberration is the problem that glass bends or refracts light of different colors different amounts. This means that light of one color is focused as a slightly different position than light of another color. One way to eliminate chromatic aberration is to substitute a mirror for the objective lens. Such a telescope was first invented by Sir Isaac Newton and is illustrated in Figures 19.20 and 19.21. A large spherical or parabolic mirror focuses the light the same as the objective lens we have just studied. A small mirror is placed in front of this objective mirror and diverts the light to one side where the image may be viewed with an eyepiece. A variation of this, called a Cassegrainian telescope, is also shown in the figure. There, a small mirror reflects the light through a hole in the objective mirror. Almost all large astronomical telescopes use mirrors, such as the one in Figure 19.22. Such reflecting telescopes have several advantages over refracting telescopes-lack of chromatic aberration, only one surface to grind and polish, and the weight of a large mirror can be supported along its back (the weight of a large lens can be supported only at its edges and this will cause a lens to "sag"). Figure 19.21 Light of all wavelengths is focused the same in a reflecting telescope like this one invented by Sir Isaac Newton. Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors.

Photoelectric conversionefficiency

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19.6 Telescope [Prev Section] [Next Section] [Table of Contents] [Chapter Contents] A telescope is used for viewing distant objects. In some sense a telescope is designed like the microscope we have just discussed. A front, objective lens produces a real image that is then viewed by an eyepiece as a simple magnifier. This is illustrated in Figure 19.17. The real image produced by the objective lens is small but it is nearby and can be observed with the eyepiece. Figure 19.17 A telescope enlarges the angular size of a distant object. Notice that the arrangement of lenses for the telescope in Figure 19.17 results in an inverted image. Most astronomical telescopes are arranged like this. It really does not matter to an Astronomer if she is viewing a star cluster upside down or right side up. However, for viewing something on Earth, a terrestrial telescope needs to have a final upright image. Binoculars often do this by reflections with prisms that correctly orient the image to be upright as well as shortening the distance between the objective and eyepiece lenses. Figure 19.18 shows another way of obtaining an upright image. Opera glasses or field glasses use this arrangement of lenses. In this arrangement, the eyepiece is a diverging lens and intercepts the light before the real image of the objective lens is produced. This arrangement is also beneficial because it shortens the distance between the lenses. Just as with an astronomical telescope, the objective lens forms a real image. While this real image is small, it is nearby so observation is far easier than for the original object. A diverging lens is now used as an eyepiece and is positioned so its focal point coincides with the real image. This produces an upright virtual image at infinity. Figure 19.19 "Opera glasses" or "field glasses" use a negative or diverging lens in the eyepiece to produce an upright image. The magnification of a telescope is given by M = fobj / feye where fobj is the focal length of the objective lens and feye is the focal length of the eyepiece. That means a large magnification results from a long focal length objective lens and a short focal length eyepiece. All lenses suffer aberrations of various kinds. chromatic aberration is the problem that glass bends or refracts light of different colors different amounts. This means that light of one color is focused as a slightly different position than light of another color. One way to eliminate chromatic aberration is to substitute a mirror for the objective lens. Such a telescope was first invented by Sir Isaac Newton and is illustrated in Figures 19.20 and 19.21. A large spherical or parabolic mirror focuses the light the same as the objective lens we have just studied. A small mirror is placed in front of this objective mirror and diverts the light to one side where the image may be viewed with an eyepiece. A variation of this, called a Cassegrainian telescope, is also shown in the figure. There, a small mirror reflects the light through a hole in the objective mirror. Almost all large astronomical telescopes use mirrors, such as the one in Figure 19.22. Such reflecting telescopes have several advantages over refracting telescopes-lack of chromatic aberration, only one surface to grind and polish, and the weight of a large mirror can be supported along its back (the weight of a large lens can be supported only at its edges and this will cause a lens to "sag"). Figure 19.21 Light of all wavelengths is focused the same in a reflecting telescope like this one invented by Sir Isaac Newton. Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors. [Prev Section] [Next Section] [Table of Contents] [Chapter Contents]

Solar panelefficiency

The efficiency of a detector in recording radiation. It is the ratio of the number of photons usefully detected to the number (of a given frequency) that strike the detector. An ideal detector would have a quantum efficiency of 1. Photographic emulsion records only a small proportion of incoming photons, and thus has a low quantum efficiency of 0.001–0.01. Electronic detectors, such as CCDs and photomultipliers, have quantum efficiencies of 0.6–0.8 and hence can record faint objects during short exposures. The quantum efficiency of the human eye is about 0.01–0.05. Quantum efficiency is frequently expressed as a percentage.

[Prev Section] [Next Section] [Table of Contents] [Chapter Contents] A telescope is used for viewing distant objects. In some sense a telescope is designed like the microscope we have just discussed. A front, objective lens produces a real image that is then viewed by an eyepiece as a simple magnifier. This is illustrated in Figure 19.17. The real image produced by the objective lens is small but it is nearby and can be observed with the eyepiece. Figure 19.17 A telescope enlarges the angular size of a distant object. Notice that the arrangement of lenses for the telescope in Figure 19.17 results in an inverted image. Most astronomical telescopes are arranged like this. It really does not matter to an Astronomer if she is viewing a star cluster upside down or right side up. However, for viewing something on Earth, a terrestrial telescope needs to have a final upright image. Binoculars often do this by reflections with prisms that correctly orient the image to be upright as well as shortening the distance between the objective and eyepiece lenses. Figure 19.18 shows another way of obtaining an upright image. Opera glasses or field glasses use this arrangement of lenses. In this arrangement, the eyepiece is a diverging lens and intercepts the light before the real image of the objective lens is produced. This arrangement is also beneficial because it shortens the distance between the lenses. Just as with an astronomical telescope, the objective lens forms a real image. While this real image is small, it is nearby so observation is far easier than for the original object. A diverging lens is now used as an eyepiece and is positioned so its focal point coincides with the real image. This produces an upright virtual image at infinity. Figure 19.19 "Opera glasses" or "field glasses" use a negative or diverging lens in the eyepiece to produce an upright image. The magnification of a telescope is given by M = fobj / feye where fobj is the focal length of the objective lens and feye is the focal length of the eyepiece. That means a large magnification results from a long focal length objective lens and a short focal length eyepiece. All lenses suffer aberrations of various kinds. chromatic aberration is the problem that glass bends or refracts light of different colors different amounts. This means that light of one color is focused as a slightly different position than light of another color. One way to eliminate chromatic aberration is to substitute a mirror for the objective lens. Such a telescope was first invented by Sir Isaac Newton and is illustrated in Figures 19.20 and 19.21. A large spherical or parabolic mirror focuses the light the same as the objective lens we have just studied. A small mirror is placed in front of this objective mirror and diverts the light to one side where the image may be viewed with an eyepiece. A variation of this, called a Cassegrainian telescope, is also shown in the figure. There, a small mirror reflects the light through a hole in the objective mirror. Almost all large astronomical telescopes use mirrors, such as the one in Figure 19.22. Such reflecting telescopes have several advantages over refracting telescopes-lack of chromatic aberration, only one surface to grind and polish, and the weight of a large mirror can be supported along its back (the weight of a large lens can be supported only at its edges and this will cause a lens to "sag"). Figure 19.21 Light of all wavelengths is focused the same in a reflecting telescope like this one invented by Sir Isaac Newton. Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors. [Prev Section] [Next Section] [Table of Contents] [Chapter Contents]

Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors.

Figure 19.19 "Opera glasses" or "field glasses" use a negative or diverging lens in the eyepiece to produce an upright image. The magnification of a telescope is given by M = fobj / feye where fobj is the focal length of the objective lens and feye is the focal length of the eyepiece. That means a large magnification results from a long focal length objective lens and a short focal length eyepiece. All lenses suffer aberrations of various kinds. chromatic aberration is the problem that glass bends or refracts light of different colors different amounts. This means that light of one color is focused as a slightly different position than light of another color. One way to eliminate chromatic aberration is to substitute a mirror for the objective lens. Such a telescope was first invented by Sir Isaac Newton and is illustrated in Figures 19.20 and 19.21. A large spherical or parabolic mirror focuses the light the same as the objective lens we have just studied. A small mirror is placed in front of this objective mirror and diverts the light to one side where the image may be viewed with an eyepiece. A variation of this, called a Cassegrainian telescope, is also shown in the figure. There, a small mirror reflects the light through a hole in the objective mirror. Almost all large astronomical telescopes use mirrors, such as the one in Figure 19.22. Such reflecting telescopes have several advantages over refracting telescopes-lack of chromatic aberration, only one surface to grind and polish, and the weight of a large mirror can be supported along its back (the weight of a large lens can be supported only at its edges and this will cause a lens to "sag"). Figure 19.21 Light of all wavelengths is focused the same in a reflecting telescope like this one invented by Sir Isaac Newton. Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors.

where fobj is the focal length of the objective lens and feye is the focal length of the eyepiece. That means a large magnification results from a long focal length objective lens and a short focal length eyepiece. All lenses suffer aberrations of various kinds. chromatic aberration is the problem that glass bends or refracts light of different colors different amounts. This means that light of one color is focused as a slightly different position than light of another color. One way to eliminate chromatic aberration is to substitute a mirror for the objective lens. Such a telescope was first invented by Sir Isaac Newton and is illustrated in Figures 19.20 and 19.21. A large spherical or parabolic mirror focuses the light the same as the objective lens we have just studied. A small mirror is placed in front of this objective mirror and diverts the light to one side where the image may be viewed with an eyepiece. A variation of this, called a Cassegrainian telescope, is also shown in the figure. There, a small mirror reflects the light through a hole in the objective mirror. Almost all large astronomical telescopes use mirrors, such as the one in Figure 19.22. Such reflecting telescopes have several advantages over refracting telescopes-lack of chromatic aberration, only one surface to grind and polish, and the weight of a large mirror can be supported along its back (the weight of a large lens can be supported only at its edges and this will cause a lens to "sag"). Figure 19.21 Light of all wavelengths is focused the same in a reflecting telescope like this one invented by Sir Isaac Newton. Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors.

Externalquantum efficiency

Figure 19.19 "Opera glasses" or "field glasses" use a negative or diverging lens in the eyepiece to produce an upright image. The magnification of a telescope is given by M = fobj / feye where fobj is the focal length of the objective lens and feye is the focal length of the eyepiece. That means a large magnification results from a long focal length objective lens and a short focal length eyepiece. All lenses suffer aberrations of various kinds. chromatic aberration is the problem that glass bends or refracts light of different colors different amounts. This means that light of one color is focused as a slightly different position than light of another color. One way to eliminate chromatic aberration is to substitute a mirror for the objective lens. Such a telescope was first invented by Sir Isaac Newton and is illustrated in Figures 19.20 and 19.21. A large spherical or parabolic mirror focuses the light the same as the objective lens we have just studied. A small mirror is placed in front of this objective mirror and diverts the light to one side where the image may be viewed with an eyepiece. A variation of this, called a Cassegrainian telescope, is also shown in the figure. There, a small mirror reflects the light through a hole in the objective mirror. Almost all large astronomical telescopes use mirrors, such as the one in Figure 19.22. Such reflecting telescopes have several advantages over refracting telescopes-lack of chromatic aberration, only one surface to grind and polish, and the weight of a large mirror can be supported along its back (the weight of a large lens can be supported only at its edges and this will cause a lens to "sag"). Figure 19.21 Light of all wavelengths is focused the same in a reflecting telescope like this one invented by Sir Isaac Newton. Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors.

Notice that the arrangement of lenses for the telescope in Figure 19.17 results in an inverted image. Most astronomical telescopes are arranged like this. It really does not matter to an Astronomer if she is viewing a star cluster upside down or right side up. However, for viewing something on Earth, a terrestrial telescope needs to have a final upright image. Binoculars often do this by reflections with prisms that correctly orient the image to be upright as well as shortening the distance between the objective and eyepiece lenses. Figure 19.18 shows another way of obtaining an upright image. Opera glasses or field glasses use this arrangement of lenses. In this arrangement, the eyepiece is a diverging lens and intercepts the light before the real image of the objective lens is produced. This arrangement is also beneficial because it shortens the distance between the lenses. Just as with an astronomical telescope, the objective lens forms a real image. While this real image is small, it is nearby so observation is far easier than for the original object. A diverging lens is now used as an eyepiece and is positioned so its focal point coincides with the real image. This produces an upright virtual image at infinity. Figure 19.19 "Opera glasses" or "field glasses" use a negative or diverging lens in the eyepiece to produce an upright image. The magnification of a telescope is given by M = fobj / feye where fobj is the focal length of the objective lens and feye is the focal length of the eyepiece. That means a large magnification results from a long focal length objective lens and a short focal length eyepiece. All lenses suffer aberrations of various kinds. chromatic aberration is the problem that glass bends or refracts light of different colors different amounts. This means that light of one color is focused as a slightly different position than light of another color. One way to eliminate chromatic aberration is to substitute a mirror for the objective lens. Such a telescope was first invented by Sir Isaac Newton and is illustrated in Figures 19.20 and 19.21. A large spherical or parabolic mirror focuses the light the same as the objective lens we have just studied. A small mirror is placed in front of this objective mirror and diverts the light to one side where the image may be viewed with an eyepiece. A variation of this, called a Cassegrainian telescope, is also shown in the figure. There, a small mirror reflects the light through a hole in the objective mirror. Almost all large astronomical telescopes use mirrors, such as the one in Figure 19.22. Such reflecting telescopes have several advantages over refracting telescopes-lack of chromatic aberration, only one surface to grind and polish, and the weight of a large mirror can be supported along its back (the weight of a large lens can be supported only at its edges and this will cause a lens to "sag"). Figure 19.21 Light of all wavelengths is focused the same in a reflecting telescope like this one invented by Sir Isaac Newton. Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors.

Spectral response

Detectivequantum efficiency

Figure 19.21 Light of all wavelengths is focused the same in a reflecting telescope like this one invented by Sir Isaac Newton. Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors.

A telescope is used for viewing distant objects. In some sense a telescope is designed like the microscope we have just discussed. A front, objective lens produces a real image that is then viewed by an eyepiece as a simple magnifier. This is illustrated in Figure 19.17. The real image produced by the objective lens is small but it is nearby and can be observed with the eyepiece. Figure 19.17 A telescope enlarges the angular size of a distant object. Notice that the arrangement of lenses for the telescope in Figure 19.17 results in an inverted image. Most astronomical telescopes are arranged like this. It really does not matter to an Astronomer if she is viewing a star cluster upside down or right side up. However, for viewing something on Earth, a terrestrial telescope needs to have a final upright image. Binoculars often do this by reflections with prisms that correctly orient the image to be upright as well as shortening the distance between the objective and eyepiece lenses. Figure 19.18 shows another way of obtaining an upright image. Opera glasses or field glasses use this arrangement of lenses. In this arrangement, the eyepiece is a diverging lens and intercepts the light before the real image of the objective lens is produced. This arrangement is also beneficial because it shortens the distance between the lenses. Just as with an astronomical telescope, the objective lens forms a real image. While this real image is small, it is nearby so observation is far easier than for the original object. A diverging lens is now used as an eyepiece and is positioned so its focal point coincides with the real image. This produces an upright virtual image at infinity. Figure 19.19 "Opera glasses" or "field glasses" use a negative or diverging lens in the eyepiece to produce an upright image. The magnification of a telescope is given by M = fobj / feye where fobj is the focal length of the objective lens and feye is the focal length of the eyepiece. That means a large magnification results from a long focal length objective lens and a short focal length eyepiece. All lenses suffer aberrations of various kinds. chromatic aberration is the problem that glass bends or refracts light of different colors different amounts. This means that light of one color is focused as a slightly different position than light of another color. One way to eliminate chromatic aberration is to substitute a mirror for the objective lens. Such a telescope was first invented by Sir Isaac Newton and is illustrated in Figures 19.20 and 19.21. A large spherical or parabolic mirror focuses the light the same as the objective lens we have just studied. A small mirror is placed in front of this objective mirror and diverts the light to one side where the image may be viewed with an eyepiece. A variation of this, called a Cassegrainian telescope, is also shown in the figure. There, a small mirror reflects the light through a hole in the objective mirror. Almost all large astronomical telescopes use mirrors, such as the one in Figure 19.22. Such reflecting telescopes have several advantages over refracting telescopes-lack of chromatic aberration, only one surface to grind and polish, and the weight of a large mirror can be supported along its back (the weight of a large lens can be supported only at its edges and this will cause a lens to "sag"). Figure 19.21 Light of all wavelengths is focused the same in a reflecting telescope like this one invented by Sir Isaac Newton. Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors. [Prev Section] [Next Section] [Table of Contents] [Chapter Contents]

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Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors.

M = fobj / feye where fobj is the focal length of the objective lens and feye is the focal length of the eyepiece. That means a large magnification results from a long focal length objective lens and a short focal length eyepiece. All lenses suffer aberrations of various kinds. chromatic aberration is the problem that glass bends or refracts light of different colors different amounts. This means that light of one color is focused as a slightly different position than light of another color. One way to eliminate chromatic aberration is to substitute a mirror for the objective lens. Such a telescope was first invented by Sir Isaac Newton and is illustrated in Figures 19.20 and 19.21. A large spherical or parabolic mirror focuses the light the same as the objective lens we have just studied. A small mirror is placed in front of this objective mirror and diverts the light to one side where the image may be viewed with an eyepiece. A variation of this, called a Cassegrainian telescope, is also shown in the figure. There, a small mirror reflects the light through a hole in the objective mirror. Almost all large astronomical telescopes use mirrors, such as the one in Figure 19.22. Such reflecting telescopes have several advantages over refracting telescopes-lack of chromatic aberration, only one surface to grind and polish, and the weight of a large mirror can be supported along its back (the weight of a large lens can be supported only at its edges and this will cause a lens to "sag"). Figure 19.21 Light of all wavelengths is focused the same in a reflecting telescope like this one invented by Sir Isaac Newton. Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors.

All lenses suffer aberrations of various kinds. chromatic aberration is the problem that glass bends or refracts light of different colors different amounts. This means that light of one color is focused as a slightly different position than light of another color. One way to eliminate chromatic aberration is to substitute a mirror for the objective lens. Such a telescope was first invented by Sir Isaac Newton and is illustrated in Figures 19.20 and 19.21. A large spherical or parabolic mirror focuses the light the same as the objective lens we have just studied. A small mirror is placed in front of this objective mirror and diverts the light to one side where the image may be viewed with an eyepiece. A variation of this, called a Cassegrainian telescope, is also shown in the figure. There, a small mirror reflects the light through a hole in the objective mirror. Almost all large astronomical telescopes use mirrors, such as the one in Figure 19.22. Such reflecting telescopes have several advantages over refracting telescopes-lack of chromatic aberration, only one surface to grind and polish, and the weight of a large mirror can be supported along its back (the weight of a large lens can be supported only at its edges and this will cause a lens to "sag"). Figure 19.21 Light of all wavelengths is focused the same in a reflecting telescope like this one invented by Sir Isaac Newton. Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors.

Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors.

Figure 19.21 Light of all wavelengths is focused the same in a reflecting telescope like this one invented by Sir Isaac Newton. Figure 19.22 Two common types of reflecting telescopes are the Newtonian and Cassegrainian telescopes illustrated here. Figure 19.23 Almost all large, modern astronomical telescopes are reflectors.