Title: Zoom lens
Abstract: The invention relates to a high-performance, large-aperture yet wide-angle zoom lens system that can be used with an electronic image pickup device in particular, a method for focusing the same. In particular, the invention is concerned with a high-performance, large-aperture yet wide-angle zoom lens system which has a zoom ratio of the order of 3 at a diagonal field angle of 75° at its wide-angle end, so that it can be used with a single-lens reflex camera using an electronic image pickup device with the number of pixels being of the order of 6,000,000. The zoom lens system comprises a first lens group G1 having negative refracting power, a second lens group G2 having positive refracting power, a third lens group G3 having negative refracting power, a fourth lens group G4 having positive refracting power and a fifth lens group G5 having positive refracting power. Upon movement of an object point, focusing is carried out with the fifth lens group G5.
Patent Number: 6,967,782 Issued on 11/22/2005 to Mihara
| Inventors:
|
Mihara; Shinichi (Tama, JP)
|
| Assignee:
|
Olympus Corporation (Tokyo, JP)
|
| Appl. No.:
|
740749 |
| Filed:
|
December 22, 2003 |
Foreign Application Priority Data
| Dec 21, 1999[JP] | 11-362681 |
| Current U.S. Class: |
359/684; 359/680; 359/683 |
| Intern'l Class: |
G02B 015/14 |
| Field of Search: |
359/684,680-683
|
References Cited [Referenced By]
U.S. Patent Documents
| 4516839 | May., 1985 | Tokumaru.
| |
| 4527867 | Jul., 1985 | Fujioka et al.
| |
| 4576444 | Mar., 1986 | Kawamura.
| |
| 5132848 | Jul., 1992 | Nishio et al.
| |
| 5229886 | Jul., 1993 | Tanaka.
| |
| 5739960 | Apr., 1998 | Tanaka.
| |
| 5805350 | Sep., 1998 | Yamamoto.
| |
| 6118592 | Sep., 2000 | Kohno et al.
| |
| 6285509 | Sep., 2001 | Nakayama et al.
| |
| 6320698 | Nov., 2001 | Suzuki.
| |
| Foreign Patent Documents |
| 2080966 | Feb., 1982 | GB.
| |
| 59229517 | Dec., 1984 | JP.
| |
| 5-107476 | Apr., 1993 | JP.
| |
| 5-323196 | Dec., 1993 | JP.
| |
| 06-102455 | Apr., 1994 | JP.
| |
Primary Examiner: Sugarman; Scott J.
Attorney, Agent or Firm: Pillsbury Winthrop Shaw Pittman LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a divisional of U.S. application Ser. No. 09/741,000, filed Dec. 21,
2000, now U.S. Pat. No. 6,687,059, the contents of which are incorporated herein
by reference in their entirety.
This application claims the benefit of Japanese application No. Hei 11-362681,
filed in Japan on Dec. 21, 1999, the contents of which are incorporated herein
by this reference.
Claims
1. A zoom lens system comprising, in order from an object side of said zoom lens
system, a first lens group having negative refracting power, a second lens group
having positive refractive power, a third lens group having negative refracting
power, a fourth lens group having positive refracting power and a fifth lens group
having positive refracting power, wherein during zooming from a wide-angle end
to a telephoto end of said zoom lens system, a space between said first lens group
and said second lens group, a space between said third lens group and said fourth
lens group, and a space between said third lens group and said fifth lens group
becomes narrow while a space between said second lens group and said third lens
group, a space between said fourth lens group and an image-formation plane, and
a space between said fifth lens group and said image-formation plane becomes wide,
and focusing on a subject is carried out by movement of said fifth lens group.
2. A zoom lens system comprising, in order from an object side of said zoom lens
system, a first lens group having negative refracting power, a second lens group
having positive refractive power, a third lens group having negative refracting
power, a fourth lens group having positive refracting power and a fifth lens group
having positive refracting power, wherein upon movement of an object point, focusing
is carried out with said fifth lens group, and conditions (1), (2), and (3) are satisfied:
where βv is a magnification of said fifth lens group upon focused on an
infinite object point at a wide-angle end of said zoom lens system, ΔL
4
is an amount of movement of said fourth lens group from said wide-angle end to
a telephoto end of said zoom lens system upon focused on an infinite object point,
ΔL
5 is an amount of movement of said fifth lens group from said
wide-angle end to said telephoto end upon focused on an infinite object point,
D
45 is an air space on an optical axis of said zoom lens system between
said fourth lens group and said fifth lens group upon focused on an infinite object
point at said telephoto end, and f
5 is a focal length of said fifth
lens group.
3. The zoom lens system according to 2, wherein said fifth lens group comprises
one positive lens component having an aspherical surface.
4. The zoom lens system according to 2, wherein said fifth lens group comprises
a positive lens component having a shape factor complying with the following condition (4):
where R
51 is a radius of curvature of a surface in said fifth lens
group which is located nearest an object side thereof, and R
52 is a
radius of curvature of a surface which is located nearest an image side thereof
in said fifth lens group.
5. A zoom lens system comprising, in order from an object side thereof, a first
lens group having negative refracting power, a second lens group having positive
refracting power, a third lens group having negative refracting power, a fourth
lens group having positive refracting power and a fifth lens group having positive
refracting power, wherein focusing on movement of an object point is carried out
at the fifth lens group, and the third lens group comprises two lens components
including a cemented concave lens component and a negative single lens component,
and satisfies the following condition (18):
where f
31 is a focal length of the cemented concave lens component
in the third lens group, and f
32 is a focal length of the negative single
lens component in the third lens group, and
the fourth lens group moves upon zooming from a wide-angle end to a telephoto
end of the zoom lens system.
6. The zoom lens system according to claim 5, wherein upon zooming from the wide-angle
end to the telephoto end of the zoom lens system, the fourth lens group moves so
as to increase a space between the fourth lens group and an image plane.
7. A zoom lens system, which comprises, in order from an object side thereof,
a first lens group having negative refracting power, a second lens group having
positive refracting power, a third lens group having negative refracting power,
a fourth lens group having positive refracting power and a fifth lens group having
positive refracting power, wherein focusing on movement of an object point is carried
out at the fifth lens group and upon zooming from a wide-angle end to a telephoto
end of the zoom lens system, the first lens group moves toward an image side of
the zoom lens system at the telephoto end rather than at the wide-angle end, the
second lens group move constantly toward the object side and the third lens group
remains fixed.
8. A zoom lens system, which comprises, in order from an object side thereof,
a first lens group having negative refracting power, a second lens group having
positive refracting power, a third lens group having refracting power, a fourth
lens group having positive refracting power and a fifth lens group having refracting
power, wherein focusing on movement on an object point is carried out at the fifth
lens group upon zooming from a wide-angle end to a telephoto end of the zoom lens
system, the first lens group moves toward an image side of the zoom lens system
at the telephoto end rather than at the wide-angle end, the second and fourth lens
group move constantly toward the object side, the third lens group remains fixed
and the second and fourth lens groups move together.
9. A zoom lens system, which comprises, in order from an object side thereof,
a first lens group having a negative refracting power, a second lens group having
positive refracting power, a third lens group having negative refracting power,
a fourth lens group having positive refracting power and a fifth lens group having
a positive refracting power, wherein focusing on movement of an object point is
carried out at the fifth lens group, upon zooming from a wide-angle end to a telephoto
end of the zoom lens system, the first lens group moves to an image side of the
zoom lens system, and the first lens group satisfies the following condition:
where f
labs is an absolute value of a focal first lens group, and
Hb
labs is an absolute value of a rear principle point position of the
first lens group.
10. A zoom lens system, which comprises, in order from an object side thereof,
a first lens group having a negative refracting power, a second lens group having
positive refracting power, a third lens group having negative refracting power,
a fourth lens group having positive refracting power and a fifth lens group having
a positive refracting power, wherein focusing on movement of an object point is
carried out at the fifth lens group, upon zooming from a wide-angle end to a telephoto
end of the zoom lens system, the first lens group moves to an image side of the
zoom lens system while the third lens group remains fixed, and the first lens group
satisfies the following condition:
where f
labs is an absolute value of a focal first lens group, and
Hb
labs is an absolute value of a rear principle point position of the
first lens group.
11. A zoom lens system comprising, in order from an object side thereof, a first
lens group having negative refracting power, a second lens group having positive
refracting power, a third lens group having negative refracting power, a fourth
lens group having positive refracting power, and a fifth lens group having a positive
refracting power, wherein focusing on movement of an object point is carried out
at the fifth lens group, upon zooming from a wide-angle end to a telephoto end
of the zoom lens system, the first lens group moves to an image side of the zoom
lens system, and the following condition is satisfied with the first and second
lens groups:
where f
labs is an absolute value of a focal length of the first lens
group, and Hb
labs is an absolute value of a rear principle point position
of the first lens group, and f
2 is a focal length of the second lens group.
12. A zoom lens system comprising, in order from an object side thereof, a first
lens group having negative refracting power, a second lens group having positive
refracting power, a third lens group having negative refracting power, a fourth
lens group having positive refracting power, and a fifth lens group having a positive
refracting power, wherein focusing on movement of an object point is carried out
at the fifth lens group, and the following condition is satisfied with the respect
to the first and second lens groups:
where f
labs is an absolute value of a focal length of the first lens
group, Hb
labs is an absolute value of a rear principle point position
of the first lens group, and f
2 is a focal length of the second lens
group, and
the fourth lens group moves upon zooming from a wide-angle end to a telephoto
end of the zoom lens system.
13. A zoom lens system comprising, in order from an object side thereof, a first
lens group having negative refracting power, a second lens group having positive
refracting power, a third lens group having negative refracting power, a fourth
lens group having positive refracting power, and a fifth lens group having positive
refracting power, wherein focusing on movement of an object point is carried out
at the fifth lens group, upon zooming from a wide-angle end to a telephoto end
of the zoom lens system, the first lens group moves toward an image side of the
zoom lens system, and at least two of the following conditions (16), (17) and (18)
are satisfied:
where f
labs is an absolute value of a focal length of the first lens
group, Hb
labs is an absolute value of a rear principle point position
of the first lens group, f
2 is a focal length of the second lens group,
f
31 is a focal length of a concave lens component in the third lens
group, and f
32 is a focal length of a negative lens component in the
third lens group.
14. The zoom lens system according to any one of claims
5 and
9-
13,
wherein upon zooming from the wide-angle end to the telephoto end, a spacing between
the first and second lens groups and a spacing between the third and fourth lens
groups become narrow while a spacing between the second and third lens groups and
a spacing between the fourth lens group and an image-formation plane become wide.
15. The zoom lens system according to any one of 9-
13, wherein upon zooming
from the wide-angle end to the telephoto end, a spacing between the first and second
lens groups and a spacing between the third and fourth lens groups become narrow
while a spacing between the second and third lens groups and a spacing between
the fourth lens group and an image-formation plane become wide, in which upon focusing
from close range in an infinite direction, the fifth lens group moves toward the
image side and upon focusing from an infinite direction in a close range direction,
the fifth lens group moves toward the object side.
16. A zoom lens system comprising, in order from an object side thereof, a first
lens group having negative refracting power, a second lens group having positive
refracting power, a third lens group having negative refracting power, a fourth
lens group having positive refracting power, and a fifth lens group having positive
refracting power, wherein focusing on movement of an object point is carried out
at the fifth lens group, and at least two of the following conditions (16), (17)
and (18) are satisfied:
where f
labs is an absolute value of a focal length of the first lens
group, Hb
labs is an absolute value of a rear principle point position
of the first lens group, f
2 is a focal length of the second lens group,
f
31 is a focal length of a concave lens component in the third lens
group, and f
32 is a focal length of a negative lens component in the
third lens group, and
the fourth lens group moves upon zooming from a wide-angle end to a telephoto
end of the zoom lens system.
17. A zoom lens system comprising, in order from an object side thereof, a first
lens group having negative refracting power, a second lens group having positive
refracting power, a third lens group having negative refracting power, a fourth
lens group having positive refracting power and a fifth lens group having positive
refracting power, wherein focusing on movement of an object point is carried out
at the fifth lens group, and a plurality of axially fixed optical devices are located
in the rear of the fifth lens group, and
upon zooming from a wide-angle end to a telephoto end of the zoom lens system,
the first lens group moves constantly toward an image side.
18. The zoom lens system according to claim 17, wherein the plurality of axially
fixed optical devices include at least a low-pass filter and an infrared cut filter.
19. A zoom lens system comprising, in order from an object side thereof, a first
lens group having negative refracting power, a second lens group having positive
refracting power, a third lens group having negative refracting power, a fourth
lens group having positive refracting power and a fifth lens group having positive
refracting power, wherein focusing on movement of an object point is carried out
at the fifth lens group, and the third lens group comprises two lens components
including a cemented concave lens component and a negative single lens component,
and satisfies the following condition (18):
where f
31 is a focal length of the cemented concave lens component
in the third lens group, and f
32 is a focal length of the negative single
lens component in the third lens group, and
the first lens group moves upon zooming from a wide-angle end to a telephoto
end of the zoom lens system.
20. The zoom lens system according to claim 19, wherein upon zooming from the
wide-angle end to the telephoto end of the zoom lens system, the first lens group
moves toward an image side.
21. A zoom lens system comprising, in order from an object side thereof, a first
lens group having negative refracting power, a second lens group having positive
refracting power, a third lens group having negative refracting power, a fourth
lens group having positive refracting power and a fifth lens group having positive
refracting power, wherein focusing on movement of an object point is carried out
at the fifth lens group, and a plurality of axially fixed optical devices are located
in the rear of the fifth lens group, and
the third lens group comprises, in order from the object side, a cemented concave
lens component and a negative single lens component.
22. A zoom lens system comprising, in order from an object side thereof, a first
lens group having negative refracting power, a second lens group having positive
refracting power, a third lens group having negative refracting power, a fourth
lens group having positive refracting power and a fifth lens group having positive
refracting power, wherein focusing on movement of an object point is carried out
at the fifth lens group, and the third lens group comprises, in order from the
object side, a cemented concave lens component and a negative single lens component,
and satisfies the following condition (18):
where f
31 is a focal length of the cemented concave lens component
in the third lens group, and f
32 is a focal length of the negative single
lens component in the third lens group.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to a zoom lens, and more particularly
to a zoom lens system that lends itself to a camera using a CCD or other electronic
image pickup device.
In recent years, digital cameras (electronic cameras) have attracted attention
as the next generation of cameras taking the place of silver halide 35 mm film
(usually called Leica size) cameras. In consumer applications in particular, zoom
lenses from a single-focus lens having a diagonal field angle of about 60°
to a wide-angle zoom lens having a zoom ratio of the order of 3 have gone mainstream.
For current higher-class zoom lenses, much is desired on their wide-angle side
or telephoto side and, at the same time, higher-grade cameras of the single-lens
reflex type are in demand. As a matter of course, higher image quality, too, is
needed. Zoom lenses suitable for use on single-lens reflex cameras having a diagonal
field angle of the order of 75°, for instance, are disclosed in JP-A's 4-163415
and 5-27175.
These publications disclose a zoom lens system comprising, in order from an
object side thereof, a first lens group having negative refracting power, a second
lens group having positive refracting power, a third lens group having negative
refracting power and a fourth lens group having positive refracting power, wherein
for zooming from the wide-angle end to the telephoto end of the zoom lens system,
the respective lens groups move in such a way that the space between the first
lens group and the second lens group, and the space between the third lens group
and the fourth lens group becomes narrow while the space between the second lens
group and the third lens group, and the space between the fourth lens group and
an image-formation plane becomes wide. This zoom lens system has a reduced F-number
of the order of 2 to 2.8.
However, the number of pixels then suggested for the single-lens reflex
type was at most about 1,000,000; the aforesaid publications do no give any suggestion
about the achievement of a zoom lens capable of taking full advantage of the performance
of an electronic image pickup device expected to have 6,000,000 or 10,000,000 pixels
at some future time.
Maintaining performance possible leads to a size increase. This point,
too, is the problem to be solved.
In consideration of loads on, and the layout of, a driving system and the effective
diameter of the first lens group, a rear focusing mode is preferable for focusing.
However, when rear focusing is carried out in the aforesaid zoom lens system wherein
the first lens group has negative refracting power, the second lens group has positive
refracting power, the third lens group has negative refracting power and the fourth
lens group has positive refracting power, some problems arise. For instance, one
problem is a fluctuation of aberrations, and another problem is that focusing becomes
impossible or the amount of movement of the focusing group should be increased
because of the presence of a zooming zone where the magnification of the fourth
lens group is equal to or close to life-size.
JP-A 4-264412 or JP-A 9-203861 discloses a zoom lens system comprising a first
lens group having negative refracting power, a second lens group having positive
refracting power, a third lens group having negative refracting power, a fourth
lens group having positive refracting power, and a fifth lens group having positive
refracting power and designed to be fixed during zooming. The zooming action is
allocated to four lens groups located on the object side of the zoom lens system.
However, these publications give no particular suggestion about focusing.
JP-A 6-102455 discloses a rear focusing zoom lens system comprising a first
lens group having negative refracting power, a second lens group having positive
refracting power, a third lens group having negative refracting power, a fourth
lens group having positive refracting power, and a fifth lens group having negative
refracting power and designed to move during zooming, wherein rear focusing is
carried out with the fifth lens group. The publication shows that the fifth lens
group is also movable toward the image side for focusing from an infinite distance
to a nearby distance. For an optical system that can be used with a CCD or other
electronic image pickup device and so is required to be of substantially telecentric
construction, it is not preferable that the lens group located nearest to the image
side has negative power, because the whole optical system becomes thick.
SUMMARY OF THE INVENTION
In view of such problems with the prior art as explained above, an object of
the
present invention is to provide a high-performance, large-aperture yet wide-angle
zoom lens system best suited for use with an electronic image pickup device in
particular. Another object of the invention is to provide a method for focusing
a high-performance, large-aperture yet wide-angle zoom lens system best suited
with an electronic image pickup device. Yet another object of the invention is
to provide a high-performance, large-aperture yet wide-angle zoom lens system which
has a zoom ratio of the order of 3 at a diagonal field angle of 75° (focal
length 28 mm class as calculated on a 35 mm size basis) at its wide-angle end,
so that it can be used with a single-lens reflex camera using a miniature electronic
image pickup device with the number of pixels being of the order of 6,000,000.
According to the present invention, the aforesaid objects are achieved
by the provision of a zoom lens system comprising, in order from an object side
of the zoom lens system, a first lens group having negative refracting power, a
second lens group having positive refracting power, a third lens group having negative
refracting power, a fourth lens group having positive refracting power and a fifth
lens group having positive refracting power, wherein upon movement of an object
point, focusing is carried out with said fifth lens group.
Why the aforesaid arrangement is used in the present invention, and how it work
is now explained.
As already pointed out with reference to the prior art, the zoom lens arrangement
of -+-+ construction is suitable for a wide-angle arrangement. In this arrangement,
the fourth lens group is divided to a fourth lens subgroup having positive refracting
power and a fifth lens subgroup having positive refracting power to reduce fluctuations
of aberrations with zooming, and ensure telecentric performance without increasing
the thickness of the whole optical system. In addition, it is possible to carry
out rear focusing (with the lens group located nearest to the image side of the
zoom lens system) while the amount of movement of the lens group is reduced with
a limited deterioration of the image formation capability upon focusing all over
the zooming area.
FIGS. 11 to 13 are geometries illustrative of the actions of the present
invention. FIG. 11 illustrates one conventional case where the first lens group
G1 is used in the form of a focusing group. As can be seen from the state
of FIG. 11(
b) where the first lens group G1 is moved out of
the state of FIG. 11(
a), the effective diameter of the first lens
group G1 must be increased for focusing. FIG. 12 illustrates another conventional
case where a zoom lens arrangement of -+-+- construction is achieved by locating
a negative lens group G1 to the image side; the first lens group G1
is used in the form of a focusing group, and shows that for a telecentric optical
system it is necessary to increase the effective diameter of the fourth lens group
G4. FIG. 13 illustrates one zoom lens arrangement of the present invention,
and shows that it provides an efficient optical system. Although not understood
from FIG. 13, the spacing layout between the fourth lens group G4 and the
fifth lens group G5 upon zooming enables fluctuations of off-axis aberrations
such as coma and field curvature to be effectively reduced. For instance, focus
detection may be carried out by not only triangulation or a phase contrast method
but also a contrast method on the basis of information obtained from an image pickup device.
In the present invention, it is preferable to satisfy any one of the following
conditions because it is easy to take full advantage of the merit of rear focusing.
Here βv is the magnification of the fifth lens group upon focused on an
infinite object point at the wide-angle end, Δ
L4 is the amount
of movement of the fourth lens group from the wide-angle end to the telephoto end
upon focused on an infinite object point, Δ
L5 is the amount of
movement of the fifth lens group from the wide-angle end to the telephoto end upon
focused on an infinite object point, D
45 is the air space on the optical
axis between the fourth lens group and the fifth lens group upon focused on an
infinite object point at the telephoto end, and f
5 is the focal length
of the fifth lens group.
It is more preferable that the following conditions should be independently satisfied.
It is most preferable that the following conditions should be independently satisfied.
The aforesaid condition (1) provides a definition of the magnification, βv,
of the fifth lens group upon focused on an infinite object point at the wide-angle
end. Exceeding the upper limit of 0.8 is not preferable because the amount of focusing
movement of the fifth lens group is likely to increase, resulting in the need of
much space. Falling below the lower limit of -0.2 is again not preferable because
the power and diameter of the fifth lens group tend to increase, resulting in a
failure in ensuring the edge of the lens.
Condition (2) provides a definition of the amount-of-movement ratio, Δ
L5/Δ
L4,
of the fifth to the fourth lens group upon movement from the wide-angle end to
the telephoto end while the system is focused on an infinite object point. The
amount of movement of the focusing (fifth) group upon focused on a nearby object
point is approximately the square of the zoom ratio at the telephoto end with respect
to the wide-angle end, and so the upper limit to this condition must be 1.2, preferably
1, and more preferably 0.9. On the other hand, a part of the zooming action of
the present zoom lens system is allocated to the combined fourth and fifth lens
groups that come close to the third lens group. However, falling below the lower
limit of 0.6 is not preferable. This is because although the movement of the fourth
lens group toward the third lens group is sufficient, the movement of the combined
fourth and fifth lens groups to the principal point is insufficient and, hence,
the zooming effect becomes slender.
Condition (3) provides a definition of the air space D
45 on
the optical axis between the fourth lens group and the fifth lens group upon focused
on an infinite object point at the telephoto end. Exceeding the upper limit of
0.15 is not preferable because of a slight decrease in the zoom ratio or an increase
in the length of the system, large fluctuations of the position of the exit pupil
with zooming, etc. Falling below the lower limit of 0.05 makes close-up impossible
because of insufficient focusing strokes.
Although the fifth lens group has a focusing function, large fluctuations
of aberrations with focusing are not preferable. In addition, the fifth lens group
takes a role in keeping the zoom lens system telecentric at the exit side. However,
it is noted that this lens group is prone to off-axis aberrations. Thus, it is
desired that the fifth lens group be made up of a positive single lens component
including an aspherical surface or, alternatively, two lenses, i.e., a negative
lens and a positive lens (which may be cemented together to form a positive doublet).
Here let R
51 stand for the radius of curvature of the surface located
nearest to the object side in the fifth lens group and R
52 represent
the radius of curvature of the surface located nearest to the image side therein.
It is then preferable to satisfy any one of the following conditions.
Any deviation from these ranges makes it impossible to place axial aberrations
and off-axis aberrations in a well-balanced state, and renders it difficult to
obtain flat characteristics all over the effective screen.
The second aspect of the high-performance, large-aperture yet wide-angle zoom
lens system according to the present invention is now explained.
According to the second aspect of the present invention, there is provided
a zoom lens system comprising, in order from an object side of the zoom lens system,
at least a first lens group having negative refracting power, a second lens group
positive refracting power, a third lens group having negative refracting power
and a fourth lens group having positive refracting power, wherein said first lens
group comprises, in order from an object side thereof, a positive lens, a negative
meniscus lens and a negative lens component defined by a cemented lens consisting
of a negative lens and a positive meniscus lens and satisfy the following conditions
to keep high image-formation capability over a wide field angle.
Here f
1 is the focal length of the first lens group, f
W is
the focal length of the zoom lens system at its wide-angle end, n
1 is
the refractive index of the medium of the positive lens located nearest to the
object side in the first lens group, R
4 is the radius of curvature of
the concave surface of the negative meniscus lens in the first lens group, and
ν
1 is the Abbe number of the medium of the positive lens located
nearest to the object side in the first lens group.
More preferably, the following conditions should be independently satisfied.
Even more preferably, the following conditions should be independently satisfied.
Condition (5) provides a definition of the whole focal length, f
1,
of the first lens group in view of the focal length, f
W, of the zoom
lens system at the wide-angle end. When the upper limit of -1.5 is exceeded, the
radius of curvature of the concave surface of the aforesaid negative meniscus lens
should be reduced to such an extent that it can hardly constructed as such and,
at the same time, various off-axis aberrations become worse. Falling below the
lower limit of -4.0 may be favorable for correction of aberrations. However, this
makes the entrance pupil likely to be located at a deep position (or located nearer
to the image plane side) and so makes the diameter of the first lens group likely
to increase excessively.
Condition (6) provides a definition of the refractive index, n
1,
of the medium of the positive lens located nearest to the object side in the first
lens group. The high-performance, large-aperture yet wide-angle zoom lens system
according to the second aspect of the present invention is likely to have a negative
Petzval sum. Exceeding the upper limit of 1.8 is unfavorable for correction of
the Petzval sum, and makes astigmatism likely to become worse. When the lower limit
of 1.55 is not reached, higher-order aberrations are likely to occur at a large
field angle.
Condition (7) provides a definition of the radius of curvature, R
4,
of the concave surface of the aforesaid negative meniscus lens in the first lens
group. The power of this surface has a dominant influence on the whole power of
the first lens group as well as on the position of the entrance pupil. Exceeding
the upper limit of 3.5 makes the entrance pupil to be located at a deep position
and so the diameter of the first lens group likely to increase excessively. When
the lower limit of 1.3 is not reached, the meniscus lens can hardly be constructed
as such simultaneously with various off-axis aberrations becoming worse.
Condition (8) provides a definition of the Abbe number, ν
1,
of the medium of the positive lens located nearest to the object side in the first
lens group. When the upper limit of 83 is exceeded, it is difficult to make correction
for longitudinal chromatic aberration as well as chromatic aberration of magnification
(a transverse aberration component proportional to an image height). When the lower
limit of 37 is not reached, some considerable non-linearity is added to the chromatic
aberration of magnification (color distortion) and so noticeable color mismatch
tends to occur on the periphery of the screen.
The high-performance, large-aperture yet wide-angle zoom lens system according
to the third aspect of the present invention is now explained.
According to the third aspect of the present invention, there is provided
a zoom lens system comprising, in order from an object side of the zoom lens system,
at least a first lens group having negative refracting power, a second lens group
having positive refracting power, a third lens group having negative refracting
power and a fourth lens group having positive refracting power, wherein said first
lens group comprises, in order from an object side thereof, a positive lens, a
negative meniscus lens, a negative lens and a positive meniscus lens, and condition
(9) is satisfied with respect to a space D
6 between said negative lens
and said positive meniscus lens in said first lens group so as to decrease the
diameter of said first lens group which tends to increase, while conditions (10)
to (13) are satisfied.
Here D
6 is the space between the negative lens and the positive meniscus
lens in the first lens group, f
1 is the focal length of the first lens
group, f
W is the focal length of the zoom lens system at its wide-angle
end, n
1 is the refractive index of the medium of the positive lens located
nearest to the object side in the first lens group, R
4 is the radius
of curvature of the concave surface of the negative meniscus lens in the first
lens group, and ν
1 is the Abbe number of the medium of the positive
lens located nearest to the object side in the first lens group.
More preferably, the zoom lens system according to this aspect should independently
satisfy the following conditions.
Even more preferably, the zoom lens system according to this aspect should independently
satisfy the following conditions.
When the lower limit of 0.5 to condition (9) is not reached, the diameter of
the first lens group is likely to increase. When the upper limit of 1.2 is exceeded,
on the other hand, the diameter of the first lens group may be decreased. However,
the inherently small diameter of the second lens group tends to become large. This
will in turn make it difficult to ensure the edge of the second lens group or the
second lens group likely to increase excessively in diameter or deteriorate.
Conditions (10) to (13) are provided for the same reasons as conditions
(5) to (8) in the second aspect of the present invention.
The high-performance, large-aperture yet wide-angle zoom lens system according
to the fourth aspect of the present invention is now explained.
According to this aspect, there is provided a large-aperture yet wide-angle
zoom lens system comprising, in order from an object side of the zoom lens system,
at least a first lens group having negative refracting power, a second lens group
having positive refracting power, a third lens group having negative refracting
power and a fourth lens group having positive refracting power, wherein said first
lens group comprises, in order from an object side thereof, a negative meniscus
lens, a negative lens, and a positive meniscus lens component consisting of a positive
lens and a negative lens that are cemented together, and satisfies conditions (14)
and (15).
Here f
1 is the focal length of the first lens group, f
W is
the focal length of the zoom lens system at its wide-angle end, and R
2 is
the radius of curvature of the concave surface of the negative meniscus lens in
the first lens group.
More preferably, the zoom lens system according to this aspect should independently
satisfy the following conditions.
Even more preferably, the zoom lens system according to this aspect should independently
satisfy the following conditions.
Condition (14) is provided for the same reasons as conditions (5) and (10),
and condition (15) that defines the radius of curvature, R
2, of the
concave surface of the negative meniscus lens in the first lens group is provided
for the same reasons as conditions (7) and (12).
If at least one aspherical surface is added to the first lens group, it is then
possible to make improvements in image-formation capabilities with no change in
the number of lenses.
It is here noted that if such a refractive index profile as defined below is
applied
to each of the zoom lens systems according to the present invention, it is possible
to make better correction for aberrations. To be more specific, the following conditions
should preferably be satisfied with respect to the absolute value, f
labs,
of the focal length of the first lens group and the absolute value, Hb
labs,
of the position of the rear principal point of the first lens group (i.e., the
distance on the optical axis between the rear principal point of the first lens
group and the surface nearest to the image side in the first lens group).
When the upper limit of 0.9 to condition (16) is exceeded, the height of a ray
incident on the second lens group becomes too large to ensure the edge of the positive
lens in the second lens group and make correction for spherical aberrations. When
the lower limit of 0.15 is not reached, the entrance pupil is located at too deep
a position where the diameter of the front lens is likely to become large.
Any one of the following conditions should preferably be satisfied in view of
the correlation between the first lens group and the second lens group. It is here
noted that f
2 is the focal length of the second lens group.
When the upper limit of 6×10
-2 mm to condition (17) is exceeded,
fluctuations of spherical aberrations, esp., chromatic spherical aberration with
zooming are likely to become large. When the lower limit of 0.7×10
-2
mm is not reached, the whole length of the zoom lens system is likely to
increase with an increase in the diameter of the front lens.
The third lens group should preferably comprise two lens components or a cemented
concave lens component and a negative single lens component, and satisfy the following condition.
Here f
31 is the focal length of the cemented concave lens component
in the third lens group, and f
32 is the focal length of the negative
single lens in the third lens group.
More preferably,
Even more preferably,
When the upper limit of 1 to condition (18) is exceeded, it is difficult to
make correction for off-axis aberrations because of an increase in the height of
a chief ray incident on the fourth lens group. When the lower limit of 0.1 is not
reached, spherical aberrations, esp., chromatic spherical aberration are likely
to become prominent in the third lens group.
Even more preferably in the present invention, at least two of the three conditions
(16), (17) and (18) should be satisfied. As a matter of course, (16′) or
(16") may be used in place of (16), (17′) or (17") may be used in place
of (17), (18′) or (18") may be used in place of (18) or the like.
Throughout the first to fourth aspects of the present invention, it is
commonly preferable that during zooming from the wide-angle end to the telephoto
end, the first lens group moves closer to the image side at the telephoto end than
at the wide-angle end, the second and fourth lens groups move constantly toward
the object side and the third lens group remains fixed. In view of the construction
of the lens barrel and from an optical standpoint, it is preferable to move the
second and fourth lens groups together. An aperture stop should preferably be located
in the vicinity of the third lens group. In other words, the aperture stop should
preferably be located in an air space on the object or image side of the third
lens group or fixed in the third lens group. Alternatively, the aperture stop may
be made integral with the second lens group.
Each of the aforesaid arrangements lends itself to a zoom lens having a zoom
ratio of at least 2.7 as well as to a zoom lens having a field angle, 2ω,
of 70° or greater at its wide-angle end. In addition, the arrangement is suitable
for a zoom lens having a reduced F-number of 3.5 or less, and preferably 2.8 or
less, all over the zooming area when the aperture stop remains open.
Still other objects and advantages of the invention will in part be obvious
and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations
of elements, and arrangement of parts which will be exemplified in the construction
hereinafter set forth, and the scope of the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional schematic illustrative of the lens arrangement of Example
1 of the zoom lens system according to the invention at its wide-angle end.
FIG. 2 is a sectional schematic illustrative of the lens arrangement of Example
2 of the zoom lens system according to the invention at its wide-angle end.
FIG. 3 is a sectional schematic illustrative of the lens arrangement of Example
3 of the zoom lens system according to the invention at its wide-angle end.
FIG. 4 is a sectional schematic illustrative of the lens arrangement of Example
4 of the zoom lens system according to the invention at its wide-angle end.
FIGS. 5(
a), 5(
b) and 5(
c) are aberration
diagrams for Example 1 upon focused at infinity.
FIGS. 6(
a), 6(
b) and 6(
c) are aberration
diagrams for Example 2 upon focused at infinity.
FIGS. 7(
a), 7(
b) and 7(
c) are aberration
diagrams for Example 3 upon focused at infinity.
FIGS. 8(
a), 8(
b) and 8(
c) are aberration
diagrams for Example 4 upon focused at infinity.
FIGS. 9(
a), 9(
b) and 9(
c) are schematics
illustrative of an electronic camera to which the zoom lens system according to
the present invention may be applied.
FIG. 10 is a schematic illustrative of a video camera to which the zoom lens
system according to the present invention may be applied.
FIGS. 11(
a) and 11(
b) are geometries illustrative
of a conventional type zoom lens wherein the first lens group is used as a focusing group.
FIG. 12 is a geometry illustrative of a conventional type zoom lens where a
negative lens group located on the image side is used as a focusing group.
FIG. 13 is a geometry illustrative of the construction of the zoom lens system
according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Examples 1 to 4 of the zoom lens system according to the present invention
are now described. Numerical data on the zoom lens system according to each example
will be enumerated later. The unit of length is mm.
FIGS. 1 to
4 are sectional schematics illustrative of the lens arrangements
of Examples 1 to 4 of the zoom lens system according to the present invention.
The zooming movement of each lens group from the wide-angle end to the telephoto
end is traced schematically by an arrow. In FIGS.
1 to
4, three plane-parallel
plates are located between the fifth lens group G
5 and the image plane.
In order from the object side of the zoom lens system, these plates provide a finder
splitter prism, a low-pass filter, and an IR cut filter, respectively.
Example 1 is directed to a zoom lens system having a focal length of 7.00
to 21.00, a field angle of 76.3° to 29.4° and an F-number of 2.04 to
2.73. As shown in FIG. 1, the first lens group G
1 is made up of a positive
meniscus lens convex on an object side thereof, a negative meniscus lens convex
on an object side thereof and a cemented lens consisting of a double-concave negative
lens and a positive meniscus lens convex on an object side thereof. The second
lens group G
2 is made up of a cemented lens consisting of a double-concave
negative lens and a double-convex positive lens, and a double-convex positive lens
with a stop S located in the rear thereof. The third lens group G
3 is made
up of a cemented lens consisting of a positive meniscus lens convex on an image
plane side thereof and a double-concave negative lens. The fourth lens group G
4
is made up of one double-convex positive lens. The fifth lens group G
5 is
made up of a cemented lens consisting of a double-convex positive lens and a negative
meniscus lens convex on an image plane side thereof. Three aspherical surfaces
are used; one at the object side-surface of the cemented lens in the first lens
group G
1, one at the object side-surface of the double-convex positive lens
in the second lens group G
2 and one at the image plane side-surface of the
double-convex positive lens in the fourth lens group G
4. During zooming
from the wide-angle end to the telephoto end of the zoom lens system, the stop
S and the third lens group G
3 remain fixed, while the first lens group G
1
moves toward the image plane side, the second lens group G
2 moves toward
the object side and the fourth and fifth lens groups G
4 and G
5 move
toward the object side, as indicated by arrows. In the meantime, the space between
the first and second lens groups G
1 and G
2, the space between the
third and fourth lens groups G
3 and G
4, and the space between the
third and fifth lens groups G
3 and G
5 becomes narrow. On the other
hand, the space between the second and third lens groups G
2 and G
3,
the space between the fourth lens group G
4 and the image plane, and the
space between the fifth lens group G
5 and the image plane becomes wide.
Upon movement of an object point, focusing is carried out with the fifth lens group
G
5. In this case, the fifth lens group G
5 is moved toward the object
side for focusing from the infinite direction to a nearby distance direction.
Example 2 is directed to a zoom lens system having a focal length of 7.00
to 21.00, a field angle of 76.3° to 29.4° and an F-number of 2.01 to
2.54. As shown in FIG. 2, the first lens group G
1 is made up of a positive
meniscus lens convex on an object side thereof, a negative meniscus lens convex
on an object side thereof and a cemented lens consisting of a double-concave negative
lens and a positive meniscus lens convex on an object side thereof. The second
lens group G
2 is made up of a cemented lens consisting of a double-concave
negative lens and a double-convex positive lens, and a double-convex positive lens
with a stop S located in the rear thereof. The third lens group G
3 is made
up of a cemented lens consisting of a positive meniscus lens convex on an image
plane side thereof and a double-concave negative lens. The fourth lens group G
4
is made up of a cemented lens consisting of a negative meniscus lens convex on
an object side thereof and a double-convex positive lens. The fifth lens group
G
5 is made up of one double-convex positive lens. Three aspherical surfaces
are used; one at the object side-surface of the cemented lens in the first lens
group G
1, one at the object side-surface of the double-convex positive lens
in the second lens group G
2 and one at the object side-surface of the double-convex
positive lens in the fifth lens group G
5. During zooming from the wide-angle
end to the telephoto end of the zoom lens system, the stop S and the third lens
group G
3 remain fixed, while the first lens group G
1 moves toward
the image plane side, the second lens group G
2 moves toward the object side
and the fourth and fifth lens groups G
4 and G
5 move toward the object
side, as indicated by arrows. In the meantime, the space between the first and
second lens groups G
1 and G
2, the space between the third and fourth
lens groups G
3 and G
4, and the space between the third and fifth
lens groups G
3 and G
5 becomes narrow. On the other hand, the space
between the second and third lens groups G
2 and G
3, the space between
the fourth lens group G
4 and the image plane, and the space between the
fifth lens group G
5 and the image plane becomes wide. Upon movement of an
object point, focusing is carried out with the fifth lens group G
5. In this
case, the fifth lens group G
5 is moved toward the object side for focusing
from the infinite direction to a nearby distance direction.
Example 3 is directed to a zoom lens system having a focal length of 7.00
to 21.00, a field angle of 76.3° to 29.4° and an F-number of 2.01 to
3.17. As shown in FIG. 3, the first lens group G
1 is made up of a double-convex
positive lens having a strong convex surface on an object side thereof, a negative
meniscus lens convex on an object side thereof, a double-concave negative lens
and a positive meniscus lens convex on an object side thereof. The second lens
group G
2 is made up of a cemented lens consisting of a double-concave negative
lens and a double-convex positive lens, and a double-convex positive lens with
a stop S located in the rear thereof. The third lens group G
3 is made up
of a cemented lens consisting of a positive meniscus lens convex on an image plane
side thereof and a double-concave negative lens, and a double-concave negative
lens. The fourth lens group G
4 is made up of a cemented lens consisting
of a double-concave negative lens and a double-convex positive lens. The fifth
lens group G
5 is made up of one positive meniscus lens convex on an object
side thereof. Three aspherical surfaces are used; one at the object side-surface
of the double-concave lens in the first lens group G
1, one at the object
side-surface of the double-convex positive lens in the second lens group G
2
and one at the object side-surface of the double-convex positive lens in the fifth
lens group G
5. During zooming from the wide-angle end to the telephoto end
of the zoom lens system, the stop S and the third lens group G
3 remain fixed,
while the first lens group G
1 moves toward the image plane side, the second
lens group G
2 moves toward the object side and the fourth and fifth lens
groups G
4 and G
5 move toward the object side, as indicated by arrows.
In the meantime, the space between the first and second lens groups G
1 and
G
2, the space between the third and fourth lens groups G
3 and G
4,
and the space between the third and fifth lens groups G
3 and G
5 becomes
narrow. On the other hand, the space between the second and third lens groups G
2
and G
3, the space between the fourth lens group G
4 and the image
plane, and the space between the fifth lens group G
5 and the image plane
becomes wide. Upon movement of an object point, focusing is carried out with the
fifth lens group G
5. In this case, the fifth lens group G
5 is moved
toward the object side for focusing from the infinite direction to a nearby distance direction.
Example 4 is directed to a zoom lens system having a focal length of 7.00
to 21.00, a field angle of 76.3° to 29.4° and an F-number of 2.01 to
2.82. As shown in FIG. 4, the first lens group G
1 is made up of two negative
meniscus lenses, each having a strong convex surface on an object side thereof
and a cemented lens consisting of a positive meniscus lens convex on an image plane
side thereof and a double-concave negative lens. The second lens group G
2
is made up of a cemented lens consisting of a negative meniscus lens convex on
an image plane side thereof and a positive meniscus lens convex on an image plane
side thereof, and a double-convex positive lens with a stop S located in the rear
thereof. The third lens group G
3 is made up of a cemented lens consisting
of a positive meniscus lens convex on an image plane side thereof and a double-concave
negative lens, and a negative meniscus lens having a strong convex surface on an
object side thereof. The fourth lens group G
4 is made up of a cemented lens
consisting of a negative meniscus lens having a strong convex surface on an object
side and a double-convex positive lens. Three aspherical surfaces are used; one
at the image plane side-surface of the second negative meniscus lens in the first
lens group G
1, one at the object side-surface of the double-convex positive
lens in the second lens group G
2 and one at the object side-surface of the
double-convex positive lens in the fourth lens group G
4. During zooming
from the wide-angle end to the telephoto end of the zoom lens system, the stop
S and the third lens group G
3 remain fixed, while the first lens group G
1
moves toward the image plane side, the second lens group G
2 moves toward
the object side and the fourth lens group G
4 moves toward the object side,
as indicated by arrows. In the meantime, the space between the first and second
lens groups G
1 and G
2, and the space between the third and fourth
lens groups G
3 and G
4 becomes narrow. On the other hand, the space
between the second and third lens groups G
2 and G
3, and the space
between the fourth lens group G
4 and the image plane becomes wide. Upon
movement of an object point, focusing is carried out from the infinite direction
to a nearby distance direction. In this case, the spaces between the first lens
group G
1 and the second to fourth lens groups G
2 to G
4 are
narrowed at the wide-angle end while the first lens group G
1
