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`(19) Japanese Patent Office (JP)
`
`(12) Publication of Unexamined
`Patent Application (A)
`
`(51)Int. Cl.6
`HHO4N
`HHO4N
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`GO2B
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`F1
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`(2006.01)
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`HHO4N 5/228
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`5/225
`HHO4N 5/225
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`13/00
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`15/00
`GO2B
`15/00
`(2006.01)
`13/18
`GO2B
`13/18
`Request for Examination Unrequested The number of Claims
`(21) Application Number
`Patent Application No.
`(71) Applicant:
`2011-250322
`
`(11) Patent Application Laid-Open
`Disclosure Number
`Japanese laid-Open Patent
`Publication Number:
`2013-106289 (P2013-106289A)
`(43) Publication Date: 2013, 5, 30
`Theme Code (Reference)
`2HO54
`2HO87
`5C122
`
`Z
`Z
`
`Continuing to last page
`
`(26 Pages)
`593034699
`KONICA MINOLTA ADVANCED
`LAYERS INC.
`Ishikawa-cho 2970, Hachioji-shi, Tokyo
`(74) Representative: 100085501
`Patent Attorney Shizuo SANO
`(74) Representative: 100128842
`Patent Attorney Yutaka INOUE
`Kenji KONNO
`Ishikawa-cho 2970, Hachioji-shi, Tokyo
`KONICA MINOLTA OPTO INC.
`Keiji MATSUZAKA
`Ishikawa-cho 2970, Hachioji-shi, Tokyo
`KONICA MINOLTA OPTO INC.
`
`(22) Filing Date
`
`2011, 11, 16
`
`(72) Inventor:
`
`(72) Inventor:
`
`Continuing to last page
`
`(54) [Title of the Invention] Imaging Apparatus
`
`(Corrected)
`(57) [Abstract]
`[Object] To provide an image having high image quality
`and high resolution over an entire wide variable power
`region.
`[Solving Means] An imaging apparatus includes single-focus
`first and second imaging optical systems LN1 and LN2 that
`face the same direction. A focal length of the second imaging
`optical system LN2 is longer than a focal length of the first
`imaging optical system LN1. Zooming is performed from a
`wide angle end to an intermediate focal length state with an
`electronic zoom by segmentation of an image acquired in the
`first imaging optical system LN1, and zooming is performed
`from the intermediate focal length state to a telescopic end
`with an electronic zoom by segmentation of an image
`acquired in the second imaging optical system. Thus,
`zooming from the wide angle end to the telescopic end is
`performed as a whole. Both of the first and second imaging
`optical systems LN1 and LN2 includes four or more lenses of
`first lenses of positive power and second lenses of negative
`power in order from an object side, the lenses nearest to the
`image side are negative lenses, and composite focal lengths of
`the first lenses and the second lenses are positive, and satisfy a
`conditional expression: 1.0 < fFw/fFm < 1.5.
`[Selected Drawing] FIG. 21
`
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`Specification
`Title of the Invention: IMAGING APPARATUS
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`TECHNICAL FIELD
`[0001]
`
`The present invention relates to an imaging apparatus. In particular, the present
`invention relates to a small-sized imaging apparatus having an electronic zoom
`function that can capture an image of a subject by an imaging device (for example, a
`solid imaging device such as a CCD (Charge Coupled Device)-type image sensor or a
`CMOS (Complementary Metal-Oxide Semiconductor)), and scale the image.
`
`BACKGROUND ART
`[0002]
`
`In recent years, with improved performance and miniaturization of imaging
`apparatuses using a solid imaging device such as a CCD-type image sensor and a
`CMOS-type image sensor, mobile phones and personal digital assistants that are
`equipped with the imaging apparatus have been widespread. In addition, further
`initialization and higher performance for the imaging optical system installed in the
`imaging apparatus are in increasing demand. Although conventional imaging
`apparatuses are single focus, a zoom function has grown in demand. However, when
`the imaging optical system having the optical zoon function is used, the optical system
`itself becomes excessively large, and requires an actuator for zoom driving. As a result,
`the imaging apparatus becomes extremely large. Therefore, it has been difficult to
`install such imaging apparatus in mobile phones or personal digital assistants.
`
`[0003]
`
`Thus, a single-focus imaging optical system having a small entire length can be
`provided with an electronic zoom function (that is, pseudo zoom function by
`segmentation of an image). However, in the case of an electronic zoom having a large
`zoom ratio, disadvantageously, the number of pixels of a segmented image becomes
`excessively small at a telescopic end. To solve the problem, Patent Document 1 to 3
`propose that a decrease in the number of pixels is prevented by installing a single-focus
`imaging optical system having two or more different focal lengths, and switching the
`electronic zoom function for each focal length. Patent Document 1 proposes a digital
`camera that includes a single focus lens and a zoom lens to gap the focal length with the
`electronic zoom. Patent Document 2 and Patent Document 3 propose an imaging
`apparatus that uses two or three single focus lenses to perform the electronic zoom.
`
`CONVENTIONAL TECHNICAL DOCUMENTS
`Patent Documents
`[0004]
`
`Patent Document 1: Japanese National Publication of International Patent
`Application No. 2008-530954
`Patent Document 2: Japanese Laid-open Publication No. 2005-99265
`Patent Document 3: Japanese Laid-open Publication No. 2007-306282
`
`SUMMARY OF THE INVENTION
`Problems to be Solved by the Invention
`
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`[0005]
`
`As described in Patent Documents 1 to 3, the high variable power imaging
`apparatus having the large number of pixels can be realized by using a plurality of
`imaging optical systems to perform the electronic zoom. However, Patent Documents
`1 to 3 fail to describe any specific configuration of the imaging optical system for
`achieving slimming-down and high image quality. The documents merely describe its
`concepts, and do not sufficiently demonstrate the feasibility of slimming-down.
`[0006]
`
`The present invention is devised in consideration of such problem, and its object
`is to provide a high-performance thin and small-sized imaging apparatus capable of
`acquiring an image of high quality and high resolution over an entire wide variable
`power region.
`
`MEANS FOR SOLVING THE PROBLEMS
`[0007]
`
`To attain the above-mentioned object, an imaging apparatus from a first aspect
`of the invention includes single-focus first and second imaging optical systems that face
`the same direction, a focal length of the second imaging optical system is longer than a
`focal length of the first imaging optical system, zooming is performed from a wide
`angle end to an intermediate focal length state with an electronic zoom by segmentation
`of an image acquired in the first imaging optical system, zooming is performed from the
`intermediate focal length state to a telescopic end with an electronic zoom by
`segmentation of an image acquired in the second imaging optical system, and zooming
`from the wide angle end to the telescopic end is performed as a whole. Both of the first
`and second imaging optical systems includes four or more lenses of first lenses of
`positive power and second lenses of negative power in order from the object side, the
`lenses nearest to the image side are negative lenses, and composite focal lengths of the
`first lenses and the second lenses are positive, and satisfy a conditional expression (1).
`
`1.0 < fFw/fFm < 1.5... (1)
`
`wherein,
`fFw: Composite focal lengths of the first lenses and the second lenses in the first
`imaging optical system, and
`fFm: Composite focal lengths of the first lenses and the second lenses in the
`second imaging optical system.
`[0008]
`
`The imaging apparatus from a second aspect of the invention is characterized by
`that, in the first aspect of the invention, following conditional expression (2A) and (2B)
`are satisfied.
`
`fFw/fw > 1... (2A)
`fFm/fm < 1... (2B)
`
`wherein,
`fw: Focal length of the entire first imaging optical system, and
`fm: Focal length of the entire second imaging optical system.
`
`[0009]
`
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`The imaging apparatus from a third aspect of the invention is characterized by
`that, in the first or second aspect of the invention, a following conditional expression (3)
`is satisfied.
`
`-0.6 < fXw/fXm < 0.5... (3)
`
`wherein,
`fXw: Focal length of the second lens from the image side in the first imaging
`optical system, and
`fXm: Focal length of the second lens from the image side in the second imaging
`optical system.
`[0010]
`
`The imaging apparatus from a fourth aspect of the invention is characterized by
`that, in any one of the first to third aspect of the invention, a following conditional
`expression (4) is satisfied.
`
`94 > 2ωw > 72... (4)
`
`wherein,
`2ωw: Entire viewing angle [deg] of the first imaging optical system.
`
`[0011]
`
`The imaging apparatus from a fifth aspect of the invention is characterized by
`that, in any one of the first to fourth aspect of the invention, the first imaging optical
`system includes four lenses of a first lens of positive power, a second lens of negative
`power, a third lens of positive power, and a four lens of negative power in order from
`the object side, and the second imaging optical system includes four lenses of a first
`lens of positive power, a second lens of negative power, a third lens of negative power,
`and a four lens of negative power in order from the object side.
`[0012]
`
`The imaging apparatus from a sixth aspect of the invention is characterized by
`that, in any one of the first to fourth aspect of the invention, the first imaging optical
`system includes five lenses of a first lens of positive power, a second lens of negative
`power, a third lens of positive power, a fourth lens of positive power, and a fifth lens
`of negative power in order from the object side, and the second imaging optical
`system includes five lenses of a first lens of positive power, a second lens of negative
`power, a third lens of positive power, a four lens of negative power, and a fifth lens of
`negative power in order from the object side.
`[0013]
`
`The imaging apparatus from a seventh aspect of the invention is characterized
`by that, in any one of the first to sixth aspect of the invention, a following conditional
`expression (5) is satisfied.
`
`0.6 < FNOw/FNOm < 1.3... (5)
`
`wherein,
`FNOw: F-number of the first imaging optical system, and
`FNOm: F-number of the second imaging optical system.
`
`[0014]
`
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`The imaging apparatus from an eighth aspect of the invention is characterized
`by that, in any one of the first to seventh aspect of the invention, a following conditional
`expression (6) is satisfied.
`
`0.7 < TLm/fm < 1.0... (6)
`
`wherein,
`TLm: Entire lens length (distance from the face nearest to the object side to the
`image face) of the second imaging optical system, and fm: Focal length of the entire
`second imaging optical system.
`[0015]
`
`The imaging apparatus from a ninth aspect of the invention is characterized by
`that, in any one of the first to eighth aspect of the invention, a following conditional
`expression (7) is satisfied.
`
`1.0 < TLw/fw < 1.4... (7)
`
`wherein,
`TLw: Entire lens length (distance from the face nearest to object side to the
`image face) of the first imaging optical system, and
`fw: Focal length of the entire first imaging optical system.
`
`[0016]
`
`The imaging apparatus from a tenth aspect of the invention is characterized by that,
`in any one of the first to ninth aspect of the invention, further including an imaging device
`that converts an optical image formed in the first and second imaging optical systems into
`an electrical signal, and the electronic zoom is performed using the signal acquired by the
`imaging device, wherein a following conditional expression (8) is satisfied.
`
`3 < PX/ZR < 6... (8)
`
`wherein,
`PX: The number of pixels (megapixel) of the imaging device, and
`ZR: Entire electronic zoom ratio (power) from the wide angle end to the
`telescopic end.
`
`EFFECT OF THE INVENTION
`[0017]
`
`The configuration of the present invention can achieve a high-performance thin
`and small imaging apparatus capable of acquiring an image of high quality and high
`resolution over a wide variable power region.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`[0018]
`
`FIG. 1 a sectional view illustrating optical configuration of a first imaging
`optical system in accordance with a first embodiment (Example 1).
`FIG. 2 a vertical aberration view illustrating the first imaging optical system in
`Example 1 at an infinite object distance.
`FIG. 3 a vertical aberration view illustrating the first imaging optical system in
`Example 1 at an object distance of 10 cm.
`
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`FIG. 4 a horizontal aberration view illustrating the first imaging optical system
`in Example 1 at the infinite object distance.
`FIG. 5 a horizontal aberration view illustrating the first imaging optical system
`in Example 1 at an object distance of 10 cm.
`FIG. 6 a sectional view illustrating optical configuration of a second imaging
`optical system in the first embodiment (Example 1).
`FIG. 7 a vertical aberration view illustrating the second imaging optical system
`in Example 1 at the infinite object distance.
`FIG. 8 a vertical aberration view illustrating the second imaging optical system
`in Example 1 at an object distance of 10 cm.
`FIG. 9 a horizontal aberration view illustrating the second imaging optical
`system in Example 1 at the infinite object distance.
`FIG. 10 a horizontal aberration view illustrating the second imaging optical
`system in Example 1 at an object distance of 10 cm.
`FIG. 11 a sectional view illustrating optical configuration of a first imaging
`optical system in a second embodiment (Example 2).
`FIG. 12 a vertical aberration view illustrating the first imaging optical system in
`Example 2 at the infinite object distance.
`FIG. 13 a vertical aberration view illustrating the first imaging optical system in
`Example 2 at an object distance of 10 cm.
`FIG. 14 a horizontal aberration view illustrating the first imaging optical system
`in Example 2 at an infinite object distance.
`FIG. 15 a horizontal aberration view illustrating the first imaging optical system
`in Example 2 at an object distance of 10 cm.
`FIG. 16 a sectional view illustrating optical configuration of a second imaging
`optical system in the second embodiment (Example 2).
`FIG. 17 a vertical aberration view illustrating the second imaging optical system
`in Example 2 at the infinite object distance.
`FIG. 18 a vertical aberration view illustrating the second imaging optical system
`in Example 2 at an object distance of 10 cm.
`FIG. 19 a horizontal aberration view illustrating the second imaging optical
`system in Example 2 at the infinite object distance.
`FIG. 20 a horizontal aberration view illustrating the second imaging optical
`system in Example 2 at an object distance of 10 cm.
`FIG. 21 a schematic view illustrating exemplified configuration of digital
`equipment including first and second imaging optical units.
`FIG. 22 an outline view illustrating exemplified configuration of the first and
`second imaging optical units including the first and second imaging optical systems.
`FIG. 23 an outline view illustrating exemplified configuration of digital
`equipment including the first and second imaging optical units.
`
`EXAMPLES FOR CARRYING OUT THE INVENTION
`[0019]
`
`An imaging apparatus according to the present invention will be described
`below. The imaging apparatus according to the present invention includes single-focus
`first and second imaging optical systems that face the same direction, a focal length fm
`of the second imaging optical system is longer than a focal length fw of the first
`imaging optical system, zooming (fw to fm) is performed from a wide angle end to an
`intermediate focal length state with an electronic zoom by segmentation of an image
`acquired in the first imaging optical system, zooming (fm to ft) is performed from the
`
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`intermediate focal length state to a telescopic end with an electronic zoom by
`segmentation of an image acquired in the second imaging optical system, and zooming
`(fw to ft) from the wide angle end to the telescopic end is performed as a whole. Both of
`the first and second imaging optical systems includes four or more lenses of first lenses
`of positive power (power: quantity defined as a reciprocal of the focal length) and
`second lenses of negative power in order from the object side, the lenses nearest to the
`image side are negative lenses, and composite focal lengths of the first lenses and the
`second lenses are positive, and satisfy a conditional expression (1). In the intermediate
`focal length state as the switch point between the first and second imaging optical
`systems, the image acquired in the second imaging optical system is preferably used.
`However, as necessary, the image acquired in the first imaging optical system may be
`used.
`
`1.0 < fFw/fFm < 1.5... (1)
`
`wherein,
`fFw: Composite focal lengths of the first lenses and the second lenses in the first
`imaging optical system, and
`fFm: Composite focal lengths of the first lenses and the second lenses in the
`second imaging optical system.
`[0020]
`
`The imaging optical system having the optical zoom function includes a large
`mechanism, which is unsuitable for portable equipment. Thus, the electronic zoom can be
`adopted. However, when the electronic zoom is performed in one imaging optical system,
`to acquire a large variable power ratio, the number of pixels at the telescopic end is too
`small, such that an excellent image cannot be acquired. Therefore, in order to achieve a
`large variable power ratio and acquire an excellent image, as well as to omit any large part
`such as a zoom drive mechanism to facilitate incorporation into small-sized portable
`equipment, a twin-lens electronic zoom function is preferably adopted.
`[0021]
`
`To acquire an excellent image, also when the electronic zoom is performed, a
`sufficient number of pixels are required. Therefore, the number of pixels before the
`electronic zoom must be sufficiently large. For example, the number of pixels is
`preferably three million pixels (3 megapixel) or more. Even when the electronic zoom
`is performed, to acquire the above-mentioned number of pixels, an imaging device (that
`is, a large-sized sensor) having a large number of pixels such as 10 megapixels is
`required. Therefore, even the device having a large number of pixels needs to have a
`high performance. For this reason, at least four lenses are needed.
`[0022]
`
`To form the imaging apparatus as a thin module, the first imaging optical
`system and the second imaging optical system also must be small. Therefore, the
`relationship between the optical systems, rather than each of them, is important. For
`achieving miniaturization and high performance, in both of the optical systems, it is
`preferred that the lens nearest to the object side is a positive lens, a negative lens is
`disposed at the image side, the composite focal lengths fFw, fFm of the first lenses and
`the second lenses are positive, and the lens nearest to the image side is a negative lens.
`[0023]
`
`As a whole, a telephoto type (the object side is positive power and the image
`side is negative power) is suitable for miniaturization. At this time, the first lens and the
`second lens that constitute a front group are the positive lens and the negative lens,
`
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`respectively, which is suitable in terms of the chromatic aberration and the
`compensation of Petzval sum. Further, one of conditions for constituting the telephoto
`type is that the lens nearest to the image side in the negative lens. At this time,
`preferably, the ratio of the focal lengths of the front group including the first and second
`lenses satisfies the conditional expression (1).
`[0024]
`
`That the ratio falls below a lower limit of the conditional expression (1) means
`that the focal length of the front group in the second imaging optical system is shorter
`than the focal length of the front group in the first imaging optical system (that is, power
`is larger). That is, since the entire focal length of the second imaging optical system is
`relatively long, positive power becomes weak as a whole. On the contrary, the
`condition for making the power larger than the power of the front group in the first
`imaging optical system having a small entire focal length is defined as the lower limit.
`By satisfying the conditional expression (1), the telephoto tendency of the second
`imaging optical system can be increased to advantageously reduce the entire length of
`the apparatus. Conversely, when the ratio exceeds un upper limit of the conditional
`expression (1), the front group in the second imaging optical system becomes too strong
`to deteriorate performance and error accuracy, failing to acquire excellent image
`quality.
`[0025]
`
`The above-mentioned characteristic configuration can realize a
`high-performance slim and small-sized imaging apparatus (for example, digital
`equipment such as digital cameras, mobile phones, and personal digital assistants)
`capable of acquiring an image of high resolution and high image quality over the entire
`wide variable power region. Conditions for acquiring such effect with a good balance,
`and achieving much higher optical performance, slimming-down, and miniaturization
`will be described below.
`[0026]
`
`Desirably, following conditional expressions (2A) and (2B) are satisfied.
`
`fFw/fw > 1... (2A)
`fFm/fm < 1... (2B)
`
`wherein,
`fw: Focal length of the entire first imaging optical system, and
`fm: Focal length of the entire second imaging optical system.
`
`[0027]
`
`The ratio of the focal length of the front group to the focal length of the entire
`system is an important factor indicating the telephoto property. That the conditional
`expressions (2A) and (2B) are satisfied means that the power of the front group of the
`first imaging optical system is smaller than the power of the entire systems, while the
`power of the second imaging optical system is larger than the power of the entire
`system. By satisfying the conditional expressions (2A) and (2B), the condition for
`reducing the entire length of the intermediate focal length state while ensuring the
`performance of the wide angle end can be satisfied.
`[0028]
`
`Desirably, a following conditional expression (3) is satisfied.
`
`-0.6 < fXw/fXm < 0.5... (3)
`
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`

`wherein,
`fXw: Focal length of the second lens from the image side in the first imaging
`optical system, and
`fXm: Focal length of the second lens from the image side in the second imaging
`optical system.
`The second lens from the image side is a lens on the object side from the lens
`nearest to the image side. It is the third lens in the four-lens configuration, and the third
`lens in the five-lens configuration.
`[0029]
`
`In the second imaging optical system, despite that the focal length of the entire
`system is long, the entire length needs to be reduced. In terms of the telephoto property,
`it is effective to satisfy the conditional expressions (1), (2A), and (2B). However, it is
`also important to identify the power of a rear group. Since the lens nearest to the image
`side is located near the image, the lens does not affect a back change due to the focal
`length and the entire length so much. However, the focal length of the lens located at
`the object side has an important role on the entire length and performance.
`[0030]
`
`A lower limit of the conditional expression (3) means that the lens power of the
`second imaging optical system is small (or negative) than the lens power of the first
`imaging optical system, and indicates its extent. By satisfying the conditional
`expression (3), the entire length of the second imaging optical system can be reduced
`while ensuring the performance of the first imaging optical system. If the ratio falls
`below the lower limit of the conditional expression (3), when the rear group has large
`negative power to respond to the performance request of the second imaging optical
`system, the entire lens configuration can largely change, failing to satisfy requirements
`for high-performance and slimming-down.
`[0031]
`
`Desirably, a following conditional expression (3a) is satisfied.
`
`-0.6 < fXw/fXm < 0... (3a)
`
`The conditional expression (3a) defines a more preferable condition range
`based on the above-mentioned terms than the range defined by the conditional
`expression (3), and is characterized by sign change. That is, the first imaging optical
`system is a positive lens, and the second imaging optical system is a negative lens.
`Although it obviously exhibits the telephoto property, this numerical range can achieve
`further miniaturization and higher performance. Therefore, preferably, by satisfying the
`conditional expression (3a), the above-mentioned effect can be further increased.
`[0032]
`
`Desirably, a following conditional expression (4) is satisfied.
`
`94 > 2ωw > 72... (4)
`
`wherein,
`2ωw: Entire viewing angle [deg] of the first imaging optical system.
`
`[0033]
`
`When the viewing angle exceeds an upper limit of the conditional expression
`(4), the wide angle of the zoom lens becomes too large, and when the viewing angle
`falls below a lower limit of the conditional expression (4), the entire focal length is
`located at the telescopic side, leading to scaling-up. In addition, when the viewing angel
`
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`at the wide angle end is small, the focal length at the intermediate position and the entire
`lens length can increase.
`[0034]
`
`More desirably, a following conditional expression (4a) is satisfied.
`
`90 > 2ωw > 75... (4a)
`
`The conditional expression (4a) defines a more preferable condition range
`based on the above-mentioned terms than the range defined by the conditional
`expression (4). Therefore, preferably, by satisfying the conditional expression (4a), the
`above-mentioned effect can be further increased.
`[0035]
`
`Desirably, the first imaging optical system includes four lenses of a first lens of
`positive power, a second lens of negative power, a third lens of positive power, and
`fourth lens of negative power in order from the object side, and the second imaging
`optical system includes four lenses of a first lens of positive power, a second lens of
`negative power, a third lens of negative power, and a fourth lens of negative power in
`order from the object side. Desirably, the first imaging optical system includes five
`lenses of a first lens of positive power, a second lens of negative power, a third lens of
`positive power, a fourth lens of positive power, and a fifth lens of negative power in
`order from the object side, and the second imaging optical system includes five lenses
`of a first lens of positive power, a second lens of negative power, a third lens of positive
`power, a fourth lens of negative power, and a fifth lens of negative power in order from
`the object side.
`[0036]
`
`As described above, when the first imaging optical system includes four lenses
`of positive, negative, positive, and negative, when the second imaging optical system
`includes four lenses of positive, negative, negative, and negative, when the first
`imaging optical system includes five lenses of positive, negative, positive, positive, and
`negative, or when the second imaging optical system includes five lenses of positive,
`negative, positive, negative, and negative, the first imaging optical system is
`advantageous for compensating field curvature and chromatic aberration, and the
`second imaging optical system has a high telephoto property and is advantageous for
`reducing the entire length.
`[0037]
`
`Desirably, a following conditional expression (5) is satisfied.
`
`0.6 < FNOw/FNOm < 1.3... (5)
`
`wherein,
`FNOw: F-number of the first imaging optical system, and
`NOm: F-number of the second imaging optical system.
`
`[0038]
`
`When F-numbers are different from each other at switching, the impression of
`blurring greatly changes, giving an unnatural feeling to the user. Thus, it is preferred
`that the F-numbers of the first and second imaging optical systems are close to each
`other so as to satisfy the conditional expression (5). To slim down the entire apparatus,
`it is advantageous to make the second imaging optical system darker than the first
`imaging optical system.
`[0039]
`
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`More desirably, a following conditional expression (5a) is satisfied.
`
`0.7 < FNOw/FNOm < 1.1... (5a)
`
`The conditional expression (5a) defines a more preferable condition range
`based on the above-mentioned terms than the range defined by the conditional
`expression (5). Therefore, preferably, by satisfying the conditional expression (5a), the
`above-mentioned effect can be further increased.
`[0040]
`
`Desirably, a following conditional expression (6) is satisfied.
`
`0.7 < TLm/fm < 1.0... (6)
`
`[0041]
`
`wherein,
`TLm: Entire lens length (distance from the face nearest to the object side (first
`face) to the image face) of the second imaging optical system, and
`fm: Focal length of the entire second imaging optical system.
`
`To slim down the second imaging optical system, the telescopic ratio needs to
`be reduced. However, in keeping a good balance with performance, the conditional
`expression (6) is preferably satisfied. When the ratio falls below a lower limit of the
`conditional expression (6), power can increase, leading to aberration deterioration.
`Further, the difference between the first and second imaging optical systems in
`performance can become large, causing image deterioration at switching.
`[0042]
`
`Desirably, a following conditional expression (7) is satisfied.
`
`1.0 < TLw/fw < 1.4... (7)
`
`wherein,
`TLw: Entire lens length (distance from the face nearest to object side to the
`image face) of the first imaging optical system, and
`fw: Focal length of the entire first imaging optical system.
`
`[0043]
`
`The first imaging optical system can be made slim. However, a too slim system
`has poor performance. To keep a good balance with the thickness of the second imaging
`optical system while keeping the performance, it is preferred that the conditional
`expression (7) is satisfied.
`[0044]
`
`Desirably, an imaging device that converts an optical image formed in each of
`the first and second imaging optical systems into an electrical signal is provided, the
`electronic zoom is performed using the signals acquired by the imaging device, and a
`following conditional expression (8) is satisfied.
`
`3 < PX/ZR < 6... (8)
`
`wherein,
`PX: The number of pixels (megapixel) of the imaging device, and
`ZR: Entire electronic zoom ratio (power) from the wide angle end to the
`telescopic end.
`
`APPL-1015 / Page 12 of 59
`APPLE INC. v. COREPHOTONICS LTD.
`
`

`

`[0045]
`
`The conditional expression (8) defines a suitable balance between the entire
`zoom ratio and the number of pixels. Generally, the image quality of about three million
`to four million pixels is demanded. To acquire an excellent image quality with the
`electronic zoom, the conditional expression (8) is desirably satisfied. When the ratio
`exceeds an upper limit of the conditional expression (8), it is difficult to ensure a
`sufficient variable power ratio with respect to the number of pixels of the sensor, failing
`to acquire a wide variable power range. When the ratio falls below a lower limit of the
`conditional expression (8), the minimum number of pixels becomes too small, failing to
`acquire a sufficiently high image quality. Here, it is assumed that the zoom ratio of the
`electronic zoom of the first imaging optical system is the same as the zoom ratio of the
`electronic zoom of the second imaging optical system, and one common imaging
`device or two imaging devices having the same number of pixels are used.
`[0046]
`
`The first and second imaging optical systems according to the present invention
`are suitable for digital equipment having an image input function (for example, imaging
`apparatuses such as mobile phones with camera, and digital cameras), and can be
`combined with the imaging device to constitute imaging optical units capable of
`optically capturing an image of a subject and outputting the captured image as an
`electri