United States Patent [19J
`Ogata et al.
`
`I 1111111111111111 11111 lllll lllll lllll 111111111111111 lllll 111111111111111111
`US005546236A
`[Ill Patent Number:
`[45] Date of Patent:
`
`5,546,236
`Aug. 13, 1996
`
`[54] WIDE-ANGLE PHOTOGRAPHIC LENS
`SYSTEM
`
`[75]
`
`Inventors: Yasuji Ogata; Toshiro Baba, both of
`Hachioji, Japan
`
`[73] Assignee: Olympus Optical Co., Ltd., Tokyo,
`Japan
`
`[21] Appl. No.: 208,836
`
`[221 Filed:
`
`Mar. 11, 1994
`
`[30]
`
`Foreign Application Priority Data
`
`Mar. 12, 1993
`Mar. 12, 1993
`Jul. 16, 1993
`
`[JP]
`[JP]
`[JP]
`
`Japan .................................... 5-077420
`Japan .................................... 5-077456
`Japan .................................... 5-197704
`
`Int. Cl.6
`..................................................... G02B 15/02
`[51]
`[52] U.S. CI . .......................... 359/794; 359/795; 359/784;
`359/785; 359/793
`[58] Field of Search ..................................... 359/794, 690,
`359/795, 793, 691, 692, 689, 784, 785
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,666,257
`
`5/1987 Tanaka et al ........................... 359/690
`
`FOREIGN PATENT DOCUMENTS
`
`56-91206
`57-116313
`59-147312
`60-176011
`64-90409
`2208616
`
`7/1981
`7/1982
`8/1984
`9/1985
`4/1989
`8/1990
`
`Japan .
`Japan .
`Japan .
`Japan .
`Japan .
`Japan .
`
`Primary Examiner-David C. Nelms
`Assistant Examiner-Vu A. Le
`Attorney, Agent, or Firm-Cushman, Darby & Cushman
`
`[57]
`
`ABSTRACT
`
`A wide-angle photographic lens system comprising a front
`lens unit having a positive refractive power, an aperture stop
`and a rear lens unit having a positive refractive power or a
`negative refractive power; the front lens unit comprising at
`least one positive lens component and at least one negative
`lens component, whereas said rear lens unit consisting of a
`positive lens component having a convex surface on the
`image side. This photographic lens system has a short total
`length (a length as measured from a first surface to an image
`side surface of the lens system and a small value of I:d (a
`distance as measured from the first surface to a final surface
`thereof), and is suited for use with collapsible mount type
`cameras.
`
`55-105216
`
`8/1980
`
`Japan.
`
`28 Claims, 11 Drawing Sheets
`
`APPL-1026 / Page 1 of 20
`APPLE INC. v. COREPHOTONICS LTD.
`
`

`

`U.S. Patent
`
`Aug. 13, 1996
`
`Sheet 1 of 11
`
`5,546,236
`
`FIG. 1
`
`FIG. 2
`
`rg
`
`r,o
`
`APPL-1026 / Page 2 of 20
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`

`

`U.S. Patent
`
`Aug. 13, 1996
`
`Sheet 2 of 11
`
`5,546,236
`
`FIG. 3
`
`FIG. 4
`
`r,
`
`rg
`
`r,o
`
`APPL-1026 / Page 3 of 20
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`

`

`U.S. Patent
`
`Aug. 13, 1996
`
`Sheet 3 of 11
`
`5,546,236
`
`FIG. 5
`
`rl
`
`r2
`
`r: 3'4
`
`r9
`
`FIG. 6
`
`APPL-1026 / Page 4 of 20
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`

`

`U.S. Patent
`
`Aug. 13, 1996
`
`Sheet 4 of 11
`
`5,546,236
`
`FIG. 7
`
`d3
`
`FIG 8
`
`d9
`
`APPL-1026 / Page 5 of 20
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`
`

`

`U.S. Patent
`
`Aug. 13, 1996
`
`Sheet 5 of 11
`
`5,546,236
`
`FIG. 9
`
`dg
`
`dg
`
`FIG. 10
`
`APPL-1026 / Page 6 of 20
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`

`

`U.S. Patent
`
`Aug. 13, 1996
`
`Sheet 6 of 11
`
`5,546,236
`
`FIG. 11
`
`d9
`
`FIG. /2A
`SPHERICAL
`ABERRATION
`
`FIG. /28 FIG. /2C F/G. /2D
`ASTIGMATISM
`DISTORTION
`LATERAL
`CHROMATIC
`ABERRATION
`•
`W31.7
`
`•
`W31.7
`
`I
`I
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`d
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`9
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`0.3
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`0.3
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`-3.0
`
`(¼) 3.
`
`-0.03
`
`0.03
`
`APPL-1026 / Page 7 of 20
`APPLE INC. v. COREPHOTONICS LTD.
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`

`

`U.S. Patent
`FIG./3A
`SPHERICAL
`ABERRATION
`
`F/ 2.90
`
`I '\___ g
`
`d
`
`r
`
`l
`
`/
`
`M
`
`Aug. 13, 1996
`
`Sheet 7 of 11
`
`W31.7 0
`
`5,546,236
`FIG./38 FIG.13C FIG./3D
`ASTIGMATISM
`DISTORTION
`LATERAL
`CHROMATIC
`ABERRATION
`•
`W31.7
`
`f
`
`g
`
`~
`J
`
`\
`\
`j
`I
`I
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`-0.3
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`0.3
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`-0.3
`
`0.3
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`-3.0 { ¾) 3.0
`
`-0.03
`
`0.03
`
`FIG. /4A
`SPHERICAL
`ABERRATION
`
`\ F/ 2.90
`
`\
`
`/
`
`\ M
`g
`
`d
`
`~
`
`FIG. /48 FJG. /4C FIG. /4D
`ASTIGMATISM
`DISTORTION
`LATERAL
`CHROMATIC
`ABERRATION
`W3!.7°
`)
`
`•
`CO 31.7
`
`5
`
`I g
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`-5.0 (°lo)
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`5.0
`
`-0.05
`
`0.0
`
`APPL-1026 / Page 8 of 20
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`

`

`U.S. Patent
`
`FIG. 15A
`SPHERICAL
`ABERRATION
`
`\ > J \
`
`d
`
`g
`
`\
`\
`\
`\
`
`Aug. 13, 1996
`
`Sheet 8 of 11
`
`5,546,236
`FIG. /58 F/G. /5C FIG./5D
`ASTIGMATISM
`DISTORTION
`LATERAL
`CHROMATIC
`ABERRATION
`•
`uJ37.6
`/
`(
`>\
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`•
`W37.6
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`-0.3
`
`0.3
`
`-3.0
`
`3.
`
`-0. 03
`
`0.03
`
`FIG./6A
`SPHERICAL
`ABERRATION
`
`/2
`
`F/ 3.60
`
`Ii
`I
`\ v- ,___,..- d
`~
`I \
`g \
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`
`FIG. /68 F/G. /6C FIG. /6D
`ASTIGMATISM
`DISTORTION
`LATERAL
`CHROMATIC
`ABERRATION
`•
`W31.7
`)
`
`W31.7
`
`I)
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`s
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`M
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`I
`l
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`I
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`-0.5
`
`0.5
`
`-5.0 (¾) 5.0
`
`-0.05
`
`0.05
`
`APPL-1026 / Page 9 of 20
`APPLE INC. v. COREPHOTONICS LTD.
`
`

`

`Aug. 13, 1996
`
`Sheet 9 of 11
`
`U.S. Patent
`FIG./7A
`SPHERICAL
`ABERRATION
`
`5,546,236
`FIG./78 FIG. /7C F/G. /7D
`ASTIGMATISM
`DISTORTION
`LATERAL
`CHROMATIC
`ABERRATION
`W31.7
`)\
`J
`
`F/2 .90
`
`g
`
`j
`M
`
`0
`
`W31.7
`
`s
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`0
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`g
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`I
`I
`I
`I
`I
`
`-OS
`
`0 .5
`
`-0.5
`
`0.5
`
`-S.O
`
`(¾) 5.0
`
`-0.0S
`
`0.05
`
`FIG.IBA
`SPHERICAL
`ABERRATION
`
`F/2.90
`
`"-- g
`
`d
`
`FIG. /BB FIG. /BC FIG. /8D
`ASTIGMATISM
`DISTORTION
`LATERAL
`CHROMATIC
`ABERRATION
`W3l.7°
`)
`J
`g
`
`-OS
`
`0.'3
`
`-0.5
`
`OS
`
`-5.0 (¾) 5.0
`
`- 0.05
`
`0.05
`
`APPL-1026 / Page 10 of 20
`APPLE INC. v. COREPHOTONICS LTD.
`
`

`

`Aug. 13, 1996
`
`Sheet 10 of 11
`
`5,546,236
`
`U.S. Patent
`F/G./9A
`SPHERICAL
`ABERRATION
`
`F/ 2.90
`
`d
`
`s
`
`I
`/
`!
`
`/\
`l -
`
`g
`
`1
`
`I
`
`FIG. /98 FIG. /9C FIG. /9D
`ASTIGMATISM
`DISTORTION
`LATERAL
`CHROMATIC
`ABERRATION
`•
`•
`W32.2 "\ W32.2
`)\
`I
`g
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`I
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`0
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`1.0
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`
`(¾) 2.
`
`-0.1
`
`0.1
`
`FIG.20A F/G.208 FIG.20C FIG.20D
`SPHERICAL
`ASTIGMATISM
`DISTORTION
`LATERAL
`ABERRATION
`CHROMATIC
`ABERRATION
`W32.2
`\
`2.2
`
`F/2.90
`
`•
`
`/ TW32.2
`I'-'
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`0
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`I
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`1.0
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`-1.0
`
`1.0
`
`-2.0
`
`(¼) 2.0
`
`-0.I
`
`0.1
`
`APPL-1026 / Page 11 of 20
`APPLE INC. v. COREPHOTONICS LTD.
`
`

`

`U.S. Patent
`FJG.2/A
`SPHERICAL
`ABERRATION
`
`1
`
`F/2.90
`
`5,546,236
`FIG.218 FIG.2/C FIG.2/D
`ASTIGMATISM
`DISTORTION
`LATERAL
`CHROMATIC
`ABERRATION
`W32.2
`\ W32.2
`
`Aug. 13, 1996
`
`Sheet 11 of 11
`
`0
`
`W32.2
`
`0
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`0
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`: \
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`l
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`
`-o.,
`
`0. I
`
`FIG. 22A FIG. 228 FIG. 22C FIG. 22D
`SPHERICAL
`ASTIGMATISM
`DISTORTION
`LATERAL
`ABERRATION
`CHROMATIC
`ABERRATION
`•
`•
`W32.2
`C.032.2
`
`"- W32.2
`
`0
`
`~ F/2.90
`
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`
`-0.J
`
`0.l
`
`APPL-1026 / Page 12 of 20
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`
`

`

`5,546,236
`
`1
`WIDE-ANGLE PHOTOGRAPHIC LENS
`SYSTEM
`
`BACKGROUND OF THE INVENTION
`
`5
`
`1. Field of the Invention
`The present invention relates to a photographic lens
`system suited for use with lens shutter cameras and so on,
`and more specifically a wide-angle photographic lens system
`which has an F number on the order of 2.8 or a high aperture
`ratio and high optical performance.
`2. Description of the Prior Art
`The conventional photographic lens system each of which
`has a single focal point and is configured for use with the
`lens shutter cameras, etc. generally have field angles on the
`orderof 60° to 64°. Though the triplet type is known well out
`of the three types of the conventional photographic lens
`systems, the triplet type photographic lens systems have F
`numbers which find a limit around 3.5. For this reason, those
`skilled in the art often select, for photographic lens system
`for use with the lens shutter cameras, the telephoto type and
`Tessar type which can have aperture ratios on the order of
`F/2.8. Known as conventional examples of the telephoto
`type photographic lens systems are lens systems which are 25
`disclosed by Japanese Patents Kokai Publication No. Sho
`56-91,206, Kokai Publication No. Sho 57-116,3 I 3 and
`Kokai Publication No. Sho 59-147,312. Further, there are
`known a large number of conventional examples of tele(cid:173)
`photo type photographic lens systems other than those
`disclosed by the Japanese patents mentioned above. Each of
`these conventional photographic lens systems consists of a
`front lens unit having a positive refractive power and a rear
`lens unit having a negative refractive power. This photo(cid:173)
`graphic lens system was originally developed as a telephoto
`lens system, but is currently applied as a wide-angle pho(cid:173)
`tographic lens system since this lens system has a merit that
`it permits locating a principal point thereof at a position
`close to an object point therefor, whereby this lens system
`can be configured so as to have a short total length and a 40
`telephoto ratio around 1. However, the telephoto type pho(cid:173)
`tographic lens system produces astigmatism, curvature of
`field and distortion in amounts too large for correction in
`practice. Therefore, the conventional photographic lens sys(cid:173)
`tems disclosed by the Japanese patents mentioned above 45
`adopt aspherical surfaces on the lens components disposed
`on the image side for correcting these aberrations. Further,
`the other conventional photographic lens systems use
`asphcrical surfaces in the front lens units and/or rear lens
`units for correcting aberrations.
`Known as the conventional Tessar type photographic lens
`systems are lens systems which arc disclosed by Japanese
`Patents Kokai Publication No. Sho 60-176,0 ll and Kokai
`Publication No. Hei 2-208,616. Each of these conventional
`Tcssar type photographic lens systems selects a composition 55
`in which an aperture stop is disposed on the image side of
`the lens system for simplifying a mechanism to move the
`lens units for focusing the photographic lens system. Since
`the Tcssar type photographic lens system has a principal
`point located therein, this type of photographic lens system 60
`has a total length larger than that of the telephoto type
`photographic lens system and is disadvantageous for con(cid:173)
`figuring a compact camera which is to use this photographic
`lens system.
`Furthermore, a lens system which was disclosed by Japa- 65
`nese Patent Kokai Publication No. Sho 64-90,409 is known
`as a lens system configured as a modified version of the
`
`35
`
`2
`triplet type photographic lens system. The photographic lens
`system disclosed by this Japanese patent is a lens system
`composed of four lens components of four lens elements
`which are obtained by dividing a third lens component of the
`triplet type photographic lens system, and has an aperture
`ratio of F/2.8. Stops are disposed in certain photographic
`lens systems which are preferred as embodiments of the lens
`system disclosed by the Japanese patent mentioned above.
`On the other hand, known as a conventional example of
`10 photographic lens system for use with single-lens reflex
`cameras is a lens system which was disclosed by Japanese
`Patent Kokai Publication No. Sho 55-105,216. This photo(cid:173)
`graphic lens system consists of the following: (i) a front lens
`unit which is composed of, in order from the object side, a
`15 positive lens component, a positive lens component and a
`negative lens component; and, (ii) a rear lens unit composed
`of a positive lens component. That is to say, this photo(cid:173)
`graphic lens system consists of four lens components of four
`lens elements or four lens components of five lens elements,
`20 and has a focal length of 40 mm and an aperture ratio of
`F/3.5.
`For configuring a lens shutter camera such that it is
`compact, it is necessary to shorten a total length of a
`photographic lens system (a length as measured from a first
`surface of the lens system to a film surface) which is to be
`used with the lens shutter camera. A shorter total length of
`the photographic lens system makes it possible to configure
`the camera so that it has smaller thickness as a whole and
`higher optical performance. For this reason, most of the
`30 conventional photographic lens systems described above are
`configured so as to have total lengths as short as possible.
`In recent years where lens barrels can be manufactured
`with high precisions and so as to have sophisticated func(cid:173)
`tions, but cameras are made compacter not only by short(cid:173)
`ening the lens barrels but also by configuring photographic
`lens systems so that they can be accommodated into camera
`bodies. Thickness of a camera, in a condition where it is
`collapsed, is determined dependently on a total length of a
`photographic lens system built therein and a distance (1:d) as
`measured from a first surface to a final surface of the
`photographic lens system. For configuring a camera com(cid:173)
`pacter, it is therefore necessary to shorten both the total
`length and 1:d of a photographic lens system which is to be
`used with the camera.
`For the reason described above, the telephoto type pho(cid:173)
`tographic lens systems which have large values of 1:d are
`unsuited for use with the collapsible mount type cameras.
`Further, the Tessar type photographic lens systems which
`50 have small values of 1:d are suited for use with the collaps(cid:173)
`ible mount type cameras, but insufficient in optical perfor(cid:173)
`mance thereof since these photographic lens systems pro(cid:173)
`duce astigmatism and curvature of field in amounts too large
`for correction even by using aspherical surfaces.
`The photographic lens system which was disclosed by
`Japanese Patent Kokai Publication No. Sho 64-90,409 has a
`small value of 1:d and is advantageous, like the Tessar type
`photographic lens systems, for use with the collapsible
`mount type cameras, but produces astigmatism and curva(cid:173)
`ture of field in large amounts and is insufficient in optical
`performance thereof.
`Though the photographic lens system disclosed by Japa-
`nese Patent Kokai Publication No. Sho 55-105,216 is con(cid:173)
`figured for use with the lens shutter cameras, this lens
`system is unsuited for use with the collapsible mount type
`cameras since the lens system has a large F-number and a
`large value of 1:d.
`
`APPL-1026 / Page 13 of 20
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`

`

`3
`SUMMARY OF THE INVENTION
`
`5,546,236
`
`4
`wherein the reference symbol DR represents thickness of the
`rear lens unit and the reference symbol f designates a focal
`length of the photographic lens system as a whole.
`The condition ( 1) defines thickness of the rear lens unit or
`a total thickness of two lens elements used for composing
`the rear lens unit when it is configured as a cemented
`doublet. The condition (1) is required for correcting astig(cid:173)
`matism. If the lower limit of the condition (1) is exceeded,
`astigmatism will be produced in a large amount. If the upper
`limit of the condition (1) is exceeded, the photographic lens
`system will have a large value of Ld and cannot be config(cid:173)
`ured compactly though an effect advantageous for correcting
`astigmatism will be obtained.
`A third type of the wide-angle photographic lens system
`according to the present invention adopts a rear lens unit
`which has a weak negative refractive power. Though the rear
`lens unit has the positive refractive power in the fundamen(cid:173)
`tal composition of the wide-angle photographic lens system
`according to the present invention, it is possible to correct
`the aberrations as favorably as in the cases of the first and
`second types of the wide-angle photographic lens system
`even when the rear lens unit has the weak negative refractive
`power. The third type wide-angle photographic lens system
`according to the preeyent invention satisfies the following
`condition (2):
`
`MJ<-5
`
`(2)
`
`10
`
`15
`
`20
`
`25
`
`A primary object of the present invention is to provide a
`wide-angle photographic lens system which has a short total
`length, a small value of Ld, a high aperture ratio and
`excellent optical performance, and is suited for use with the 5
`collapsible mount type cameras.
`The Tessar type photographic lens system which uses an
`aperture stop disposed on the image side of the lens system
`is apt to produce pin cushion type distortion since it com(cid:173)
`prises the front lens unit having the positive refractive power
`a rear lens unit having a positive refractive power and an
`aperture stop, and has a composition asymmetrical with
`regard to the aperture stop. Since this distortion is corrected
`by a third surface (an object side surface of a second
`negative lens component) disposed in the conventional
`Tessar type photographic lens system, the third surface
`produces coma and astigmatism, thereby, making it difficult
`to enhance optical performance of the Tessar type photo(cid:173)
`graphic lens system. In a case where the Tessar type pho(cid:173)
`tographic lens system has a larger aperture, in particular, it
`is more difficult to correct these aberrations favorably.
`In a fundamental composition of the photographic lens
`system according to the present invention, both a front lens
`unit and a rear lens unit have positive refractive powers, and
`are disposed symmetrically with regard to an aperture stop.
`In this composition of the photographic lens system, off(cid:173)
`axial aberrations are corrected favorably by cancelling the
`off-axial aberrations produced by the front lens unit with
`those produced by the rear lens unit. It is further necessary
`for correcting spherical aberration to compose the front lens
`unit so as to comprise at least one positive lens component
`and at least one negative lens component. When the photo(cid:173)
`graphic lens system according to the present invention is
`composed as described above, spherical aberration is cor(cid:173)
`rected by the front lens unit, whereas coma, astigmatism and
`distortion are corrected by cancelling these aberrations pro- 35
`duced by the front lens unit wiih those produced by the rear
`lens unit.
`On the other hand, it is desirable for reducing a value of
`Ld of the photographic lens system to compose the rear lens 40
`unit of a single lens component and configure this lens
`component as a cemented lens component for correcting
`chromatic aberration.
`Now, the composition of the rear lens unit will be
`described below in more detailed.
`The wide-angle photographic lens system according to the
`present invention can be of three types which are different
`from one another in the composition of the rear lens unit. In
`case of a first type of the wide-angle photographic lens
`system, the rear lens unit is composed only of a single 50
`meniscus lens component which has a positive refractive
`power and a convex surface on the object side. In this case,
`aberrations which are produced by the front lens unit are to
`be corrected with the rear lens unit and this lens unit must
`be configured so as to produce aberrations in excessive
`amounts though these aberrations produce adverse influ(cid:173)
`ences on the photographic lens system. In the case of the first
`type wide-angle photographic lens system, the aberrations
`can be corrected adequately by selecting the above-de(cid:173)
`scribed shape of the meniscus lens component for the rear
`lens unit.
`In case of a second type of the wide-angle photographic
`lens system according to the present invention, the rear lens
`component is composed of a lens component which is thick
`on an optical axis and satisfies the following condition (1):
`
`30
`
`wherein the reference symbol fR represents a focal length of
`the rear lens unit and the reference symbol f designates a
`focal length of the photographic lens system as a whole.
`If the negative refractive power of the rear lens unit is
`strong enough to exceed the range defined by the condition
`(2), the photographic lens system will be of the telephoto
`type described with reference to the prior art and cannot
`accomplish the object of the present invention.
`For the wide-angle photographic lens system according to
`the present invention comprising the front lens unit which
`comprises at least one positive lens component and at least
`one negative lens component, it is desirable that the front
`lens unit is composed, in order from the object side, of a first
`positive lens component, a second negative lens component
`and a third positive lens component. When the front lens unit
`is composed as described above, each of the first through
`third lens components may be composed of a single lens
`45 element or configured as a cemented doublet. In this case,
`aberrations can be corrected more favorably in the wide(cid:173)
`angle photographic lens system according to the present
`invention.
`When the front lens unit is of the triplet type of Tessar
`type, for example, aberrations are produced in large amounts
`by each lens surface but aberrations produced by different
`lens surfaces are cancelled with one another, whereby the
`aberrations are corrected in the front lens unit as a whole.
`When each of the lens surfaces produces aberrations in large
`55 amounts, however, aberrations will remain in rather large
`amounts. These residual aberrations can be corrected favor(cid:173)
`ably so as to obtain favorably corrected aberrations in the
`wide-angle photographic lens system as a whole by com(cid:173)
`posing the rear lens unit of a positive meniscus lens com-
`60 ponent which has a convex surface on the object side.
`Further, by composing the front lens unit of three lens
`components each of which is configured as a meniscus lens
`component having a convex surface on the object side, it is
`possible to reduce angles of incidence of off-axial rays and
`65 amounts of aberrations to be produced by the lens surfaces.
`It is therefore possible to correct aberrations much more
`favorably by reducing the aberrations to be produced by the
`
`0.l<D,IJ<0.3
`
`(!)
`
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`
`

`

`5,546,236
`
`6
`having the convex surface on the object side, it is possible
`to shift the principal point of the photographic lens system
`toward the object side so as to permit shortening a total
`length of the photographic lens system.
`Further, for reserving a sufficient amount of marginal rays
`on the image side of a photographic lens system, it is
`necessary to enlarge a diameter of a light bundle passing
`through the lens system. In the case of the triplet type or
`Tessar type photographic lens system, it is necessary to
`increase an amount of lower rays which pass through the
`lens system, but such increase of the lower rays will result
`in production of coma in a larger amount. It is remarkably
`effective for correcting this coma to use an aspherical
`surface or a plurality of aspherical surfaces in the front lens
`unit. For the correction of coma, it is desirable to select for
`the aspherical surface or surfaces such a shape or shapes as
`to strengthen negative refractive power or weaken positive
`refractive power as portions of the aspherical surface or
`surfaces are farther from the optical axis.
`Further, it is desirable that the first lens component of the
`front lens unit satisfies the following condition (5):
`
`(5)
`
`5
`lens surfaces and composing the rear lens unit of a thick lens
`component as in the case of the above-described second type
`of wide-angle photographic lens system according to the
`present invention.
`Furthermore, it is desirable to configure the front lens unit 5
`so as to be of the triplet type or Tessar type even in the case
`of the third type of the wide-angle photographic lens system
`according to the present invention, that is to say, in the case
`that the rear lens unit of the lens system has a weak negative
`refractive power.
`Moreover, it is desirable for each of the first type, second
`type and third type of the wide-angle photographic lens
`systems according to the present invention that the front lens
`unit satisfies the following condition (3):
`
`10
`
`(3) 15
`
`wherein the reference symbols r2a and r2b represent radii of
`curvature on the most object side surface and the most image
`side surface respectively of the second lens component
`having the negative refractive power; these surfaces being 20
`air-contact surfaces when the second lens component is
`configured as a cemented component.
`The condition (3) defines a shape for the second negative
`lens component, which must have an image side surface
`having high curvature, of the front lens unit. If the lower 25
`limit of the condition (3) is exceeded, both the surfaces of
`the negative lens component will have radii of curvature
`which progressively become equal to each other and have
`small values, whereby these surfaces will produce aberra(cid:173)
`tions in amounts too large to be corrected by the other lens 30
`surfaces. These aberrations cannot be corrected by the other
`surfaces. If the upper limit of the condition (3) is exceeded,
`spherical aberration cannot be corrected by the image side
`surface of the negative lens component and the object side
`surface of this lens component will produce off-axial aber- 35
`rations in large amounts, thereby making it difficult to
`correct aberrations in the wide-angle photographic lens
`system as a whole.
`In addition, it is desirable for the wide-angle photographic
`lens system according to the present invention to satisfy the 40
`following condition (4):
`
`wherein the reference symbol r 1a represents a radius of
`curvature on the object side surface of the first lens com(cid:173)
`ponent of the front lens unit; the surface being an air-contact
`surface when the first lens component is configured as a
`cemented lens component.
`The condition (5) is required for correcting spherical
`aberration. In the wide-angle photographic lens system
`according to the present invention, spherical aberration is
`remarkably undercorrected due to a strong converging func(cid:173)
`tion which is imparted to the object side surface of the first
`lens component of the front lens unit. For correcting this
`spherical aberration, it is necessary that a strong diverging
`function is imparted to the image side surface of the second
`lens component and that the ratio r 1jr2 b between radii of
`curvature on both the surfaces satisfies the condition (5). If
`the lower limit of the condition (5) is exceeded, spherical
`aberration will be undercorrected. If the upper limit of the
`condition (5) is exceeded, in contrast, spherical aberration
`will be overcorrected.
`When the wide-angle photographic lens system according
`to the present invention adopts the front lens unit composed
`45 of three lens components each of which is configured as a
`meniscus lens component, it is desirable that the front lens
`unit satisfies the following conditions (6) and (7):
`
`(4)
`
`wherein the reference symbol NP represents a mean value of
`refractive indices of all the positive lens elements disposed
`in the photographic lens system.
`The condition (4) is required for adequately correcting
`curvature of field.
`Since Pctzval's image surface is tilted underside in the 50
`composition selected for the wide-angle photographic lens
`system according to the present invention, it is necessary to
`select refractive indices which are high to certain degrees for
`the positive lens elements so as to satisfy the condition (4).
`By selecting the composition which has been described 55
`above, the present invention has succeeded in providing the
`wide-angle photographic lens system having favorably cor(cid:173)
`rected aberrations. In the wide-angle photographic lens
`system according to the present invention, the pin cushion
`distortion and negative astigmatism which are produced by 60
`the front lens unit arc reasonably cancelled with barrel form
`distortion produced with the rear lens unit. Owing to this
`correction mode, the wide-angle photographic lens system
`according to the present invention can assure high and
`uniform image quality over the entire range of an image 65
`surface thereof. Further, by configuring the first lens com(cid:173)
`ponent of the front lens unit as a meniscus lens component
`
`- I <(r lb-r2al/(r lb +r 2al<--O. l
`
`(6)
`
`(7)
`
`wherein the reference symbol r 1b represents a radius of
`curvature on an image side surface of the first lens compo(cid:173)
`nent, and the reference symbols r3a and r3 b designate radii of
`curvature on an object side surface and an image side surface
`respectively of the third lens component; these surfaces
`being air-contact surfaces when the third lens component is
`configured as a cemented lens component.
`The condition (6) defines a shape of an air lens disposed
`between the first lens component and the second lens
`component, and is required for correcting coma, astigmatism
`and distortion. If the air lens has a refractive power strong
`enough to exceed the lower limit of the condition (6), an
`object side surface of the second lens component will
`produce aberrations in remarkable amounts, thereby making
`it difficult to correct aberrations favorably in the photo(cid:173)
`graphic lens system as a whole. If the air lens has a refractive
`
`APPL-1026 / Page 15 of 20
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`

`5,546,236
`
`7
`power weak enough to exceed the upper limit of the con(cid:173)
`dition ( 6), the aberration correcting function of the front lens
`unit will be lowered, thereby making it difficult to correct
`aberrations favorably in the photographic lens system as a
`whole.
`The condition (7) defines a shape of the third lens com(cid:173)
`ponent. This condition is required for adequately suppress(cid:173)
`ing production of coma in a remarkable amount by the object
`side surface of the third lens component and production of
`distortion in a remarkable amount by the image side surface
`of the third lens unit, thereby correcting aberrations favor(cid:173)
`ably in the photographic lens system as a whole. If the upper
`limit or the lower limit of the condition (7) is exceeded, the
`coma or distortion which is produced by the third lens
`component will be unbalanced.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 through FIG. 11 show sectional views illustrating
`compositions of a first embodiment through an eleventh
`embodiment respectively of the wide-angle photographic
`lens system according to the present invention;
`FIG. 12 through FIG. 22 show graphs illustrating aber(cid:173)
`ration characteristics of the first through eleventh embodi(cid:173)
`ments of the present invention.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`Now, the wide-angle photographic lens system according
`to the present invention will be described in more detail
`below with reference to the preferred embodiments illus(cid:173)
`trated in the accompanying drawings and given in the form
`of the following numerical data:
`
`Embodiment I
`
`f = 35.0, fH = 26.1, F/2.9, 2co = 63.4°
`r1 = 14.1000
`
`ct,= 3.700
`
`n 1 = 1.79952
`
`v, = 42.24
`
`8
`-continued
`
`dz= 1.900
`
`d3 = 1.000
`
`d4 = 1.200
`
`d5 = 3.000
`
`Oz= J.76182
`
`Vz = 26.52
`
`03 = 1.79952
`
`Y3 = 42.24
`
`d 6 = 1.000
`
`04 = 1.51742
`
`Y4=52.41
`
`d7 = 1.000
`
`d8 = 2.000
`
`r3 = -47.1350
`
`5
`
`r4 = 12.3260
`
`r5 = 33.2200
`
`r6 = -14.4170
`
`10
`
`r7 = -39.5590
`
`r8 ==(stop)
`
`r9 = -10.4140
`
`d9 = 1.500
`
`r 10 = -10.3300
`aspherical surface coefficients
`
`15
`
`05 = 1.51633
`
`V5 = 64.15
`
`(2th surface)
`
`P = 1.0000, A4 = 0.97649 x 10-6
`A6 ---0.63052 X 10-1
`,
`As ---0.66268 x 10-9, A 10 = 0.0000
`DR/f = 0.043, fR/f 10.009, (rz, - rzb)/(rz, + r2b) = 1.708
`20 NP= 1.701, r1,/r2b = 1.081, (r1b - rz0 )/(r1b + rzal = -39.442,
`(r3a - r3b)/(r3 0 + r3b) = -11.481
`Embodiment 3
`
`f = 35.0, fH = 23.9, F/2.9, 2co = 63.4°
`r1 = 12.2960
`
`d1 = 3.500
`
`n1 = 1.80400
`
`d2 = 2.200
`
`d3 = 1.000
`
`Oz= J.76182
`
`Y2 = 26.52
`
`25
`
`30
`
`r2 = 31.1960
`
`r 3 = -42. 7320
`
`r4 = 10.9260
`
`d4 = 0.750
`r5 = 22.7090 (asphcrical surface)
`d5 = 4.000
`
`r6 = -24.2240
`
`03 = 1.83400
`
`Y3 = 37.16
`
`r7 ==(stop)
`
`35
`
`rg = -9.4810
`
`d6 = 1.000
`
`d7 = 2.000
`
`d8 = 1.500
`
`r9 = -10.2580
`asphcrical surface coefficients
`
`04 = 1.49241
`
`Y4 = 57.66
`
`P = 1.0000, A4 = 0.25892 X 10-4,
`A6 = 0.26583 x 10-5, A8 = ---0.12446 X 10-6 ,
`A 10 = 0.25845 X 10-•
`DR/f = 0.043, fR/f = -20.005, (r2, - rzb)/(rz, + rzb) = 1.687,
`NP= 1.819, r,)rzb = 1.125, (r1b - r2 0 )/(r1b + r2.) = -6.408,
`(r3a - r3b)/(r3 0 + r3b) = -30.979
`Embodiment 4
`
`f = 28.0, f8 = 18.8, F/2.9, 2ro = 75.3°
`r1 = 13.3690 (aspherical surface)
`d1 = 5.000
`
`rz = 43.1940
`
`dz== 1.600
`
`r3 = 590.2440
`
`d3 = 1.000
`r4 = 8.4700 (aspherical surface)
`d4 = 1.100
`
`r5 = 18.4000
`