U.S. patent application number 09/769456 was filed with the patent office on 2001-08-23 for zoom lens system.
Invention is credited to Enomoto, Takashi.
Application Number | 20010015857 09/769456 |
Document ID | / |
Family ID | 18546550 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010015857 |
Kind Code |
A1 |
Enomoto, Takashi |
August 23, 2001 |
Zoom lens system
Abstract
A zoom lens system includes a first lens group, a second lens
group, and a third lens group, in this order from the object.
Zooming is performed by moving the first through third lens groups.
The zoom lens system satisfies the following conditions: 1 0.62
< ( d T12 - d W12 ) / f W < 1.0 ( 1 ) 4 < f T / f 12 T
< 6 ( 2 ) 5 < f T / f 3 G < 8 ( 3 ) wherein d.sub.T12
designates the distance between the first and the second lens
groups at the long focal length extremity; d.sub.W12 designates the
distance between the first and the second lens groups at the short
focal length extremity; f.sub.W designates the focal length of the
entire zoom lens system at the short focal length extremity;
f.sub.T designates the focal length of the entire zoom lens system
at the long focal length extremity; f.sub.12T designates the
combined focal length of the first lens group and the second lens
group at the long focal length extremity; and f.sub.3G designates
the focal length of the negative third lens group.
Inventors: |
Enomoto, Takashi; (Chiba,
JP) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN
1941 ROLAND CLARKE PLACE
RESTON
VA
20191
|
Family ID: |
18546550 |
Appl. No.: |
09/769456 |
Filed: |
January 26, 2001 |
Current U.S.
Class: |
359/689 ;
359/695 |
Current CPC
Class: |
G02B 15/143103
20190801 |
Class at
Publication: |
359/689 ;
359/695 |
International
Class: |
G02B 015/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 28, 2000 |
JP |
2000-19917 |
Claims
What is claimed is:
1. A zoom lens system comprising a positive first lens group, a
positive second lens group, and a negative third lens group, in
this order from an object, wherein zooming is performed by moving
said first through said third lens groups in the optical axis
direction, and wherein said zoom lens system satisfies the
following conditions: 3 0.62 < ( d T12 - d W12 ) / f W < 1.0
4 < f T / f 12 T < 6 5 < f T / f 3 G < 8 wherein
d.sub.T12 designates the distance between said first lens group and
said second lens group at the long focal length extremity;
d.sub.W12 designates the distance between said first lens group and
said second lens group at the short focal length extremity; f.sub.W
designates the focal length of the entire zoom lens system at the
short focal length extremity; f.sub.T designates the focal length
of the entire zoom lens system at the long focal length extremity;
f.sub.12T designates the combined focal length of said first lens
group and said second lens group at the long focal length
extremity; and f.sub.3G designates the focal length of said
negative third lens group.
2. The zoom lens system according to claim 1, satisfying the
following condition: 0.7<d.sub.T12/f.sub.W<1.0
3. The zoom lens system according to claim 1, wherein the
most-object side surface of said positive first lens group is a
concave surface, and said concave surface satisfies the following
condition: -5<r1l/f.sub.W<-1 wherein r1 designates the radius
of curvature of the most-object side concave surface of said first
lens group.
4. The zoom lens system according to claim 1, wherein the
most-object side lens element of said positive first lens group is
a negative lens element, and said negative lens element satisfies
the following condition: -0.7<f.sub.1P/f.sub.W<-0.1 wherein
f.sub.1P designates the focal length of the most-object side
negative lens element of said first lens group.
5. The zoom lens system according to claim 1, wherein said positive
first lens group comprises a negative first single lens element,
and a positive single lens element, in this order from said
object.
6. The zoom lens system according to claim 1, wherein said positive
second lens group comprises a lens element having at least one
aspherical surface, and said aspherical surface satisfies the
following condition: -1000<.DELTA.IASP<-500 wherein
.DELTA.IASP designates the amount of change of the spherical
aberration coefficient due to the aspherical surface under the
condition that the focal length of the entire zoom lens system at
the long focal length extremity is converted to 1.0.
7. The zoom lens system according to claim 1, wherein said negative
third lens group comprises a lens element having at least one
aspherical surface, and said aspherical surface satisfies the
following condition: 0<.DELTA.VASP<0.2 wherein .DELTA.VASP
designates the amount of change of the distortion coefficient due
to the aspherical surface under the condition that the focal length
of the entire zoom lens system at the short focal length extremity
is converted to 1.0.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a zoom lens system for a
compact camera.
[0003] 2. Description of the Related Art
[0004] In a zoom lens system for a compact camera, in addition to a
requirement of an increased zoom ratio, a shorter focal length at
the short focal length extremity has been required in recent years.
In a zoom lens system for a single lens reflex (SLR) camera, a
retrofocus zoom lens system including a negative front lens group
and a positive rear lens group, in this order from the object, has
been employed, since a long back focal distance is required to
secure a space for providing a mirror. Unlike a SLR camera, a
compact camera does not require a long back focal distance, so that
a telephoto zoom lens system including a positive front lens group
and a negative rear lens group, in this order from the object, is
suitable for a zoom lens system thereof.
[0005] For compact cameras, conventional zoom lens systems with a
zoom ratio of about 3 have employed a three-lens-group arrangement.
The main reason for this tendency is that the correcting of field
curvature over the entire zooming range is difficult if an attempt
is made to achieve a high zoom ratio in a two-lens-group
arrangement. In contrast to the two-lens-group arrangement, with
the three-lens-group arrangement, by varying the distance between
the first lens group and the second lens group, the correcting of
field curvature can easily be made even if a high zoom ratio is
set.
[0006] However, if an attempt is further made to obtain a zoom
ration of about 4, the change in the distance between the first and
second lens groups becomes longer, thereby the overall length of
the zoom lens system becomes long. Furthermore, if the half angle
of view at the short focal length extremity exceeds 350, since the
diameters of the first and second lens groups are increased in
order to collect peripheral illumination, the size of the entire
zoom lens system is inevitably increased, which results in an
increase of both camera thickness (front-to-back length) and height
(up-to-bottom length) for accommodating the zoom lens system.
SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to provide a small
three-lens-group zoom lens system of telephoto type which has a
zoom ratio of about 4.0, and has the half angle of view at the
short focal length extremity is more than 35.degree..
[0008] According to the present invention, the following effects
(i) to (iii) can be attained by determining the optical power
(hereinafter, power) of the third lens group, and the combined
power of the first and second lens groups so that a sufficient
space is secured between the first and second lens groups to move,
while the overall length and diameter of the lens system can be
reduced:
[0009] (i) a high zoom ratio, e.g., about 4;
[0010] (ii) a shorter focal length at the short focal length
extremity, e.g., the half angle of view thereat more than
35.degree.; and
[0011] (iii) miniaturization of the lens system.
[0012] In order to achieve the above-mentioned object, there is
provided a zoom lens system including a positive first lens group,
a positive second lens group, and a negative third lens group, in
this order from the object. Zooming is performed by moving the
first through third lens groups in the optical axis direction. The
zoom lens system satisfies the following conditions: 2 0.62 < (
d T12 - d W12 ) / f W < 1.0 ( 1 ) 4 < f T / f 12 T < 6 ( 2
) 5 < f T / f 3 G < 8 ( 3 )
[0013] wherein
[0014] d.sub.T12 designates the distance between the first lens
group and the second lens group at the long focal length
extremity;
[0015] d.sub.W12 designates the distance between the first lens
group and the second lens group at the short focal length
extremity;
[0016] f.sub.W designates the focal length of the entire zoom lens
system at the short focal length extremity;
[0017] f.sub.T designates the focal length of the entire zoom lens
system at the long focal length extremity;
[0018] f.sub.12T designates the combined focal length of the first
lens group and the second lens group at the long focal length
extremity; and
[0019] f.sub.3G designates the focal length of the negative third
lens group.
[0020] The zoom lens system preferably satisfies the following
condition:
0.7<d.sub.T12/f.sub.W<1.0 (4)
[0021] The most-object side surface of the positive first lens
group can be a concave surface facing towards the object, and the
most-object side concave surface preferably satisfies the following
condition:
-5<r1/f.sub.W<-1 (5)
[0022] wherein
[0023] r1 designates the radius of curvature of the most-object
side concave surface of the first lens group.
[0024] The most-object side lens element of the positive first lens
group can be a negative lens element, and this negative lens
element preferably satisfies the following condition:
-0.7<f.sub.1P/f.sub.W<-0.1 (6)
[0025] wherein
[0026] f.sub.1P designates the focal length of the most-object side
negative lens element of the first lens group.
[0027] The positive first lens group can include a negative first
lens element and a positive second lens element, in this order from
the object.
[0028] In the positive second lens group can include a lens element
having at least one aspherical surface, and the aspherical surface
preferably satisfies the following condition:
-1000<.DELTA.IASP<-500 (7)
[0029] wherein
[0030] .DELTA.IASP designates the amount of change of the spherical
aberration coefficient due to the aspherical surface under the
condition that the focal length of the entire zoom lens system at
the long focal length extremity is converted to 1.0.
[0031] In the negative third lens group can include a lens element
having at least one aspherical surface, and the aspherical surface
preferably satisfies the following condition:
0<.DELTA.VASP<0.2 (8)
[0032] wherein
[0033] .DELTA.VASP designates the amount of change of the
distortion coefficient due to the aspherical surface under the
condition that the focal length of the entire zoom lens system at
the short focal length extremity is converted to 1.0.
[0034] The present disclosure relates to subject matter contained
in Japanese Patent Application No. 2000-019917 (filed on Jan. 28,
2000) which is expressly incorporated herein by reference in its
entirety.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The invention will be discussed below in detail with
reference to the accompanying drawings, in which:
[0036] FIG. 1 is a lens arrangement of the zoom lens system
according to a first embodiment of the present invention;
[0037] FIGS. 2A, 2B, 2C and 2D show aberrations, at the short focal
length extremity, of the lens arrangement shown in FIG. 1;
[0038] FIGS. 3A, 3B, 3C and 3D show aberrations, at an intermediate
focal length, of the lens arrangement shown in FIG. 1;
[0039] FIGS. 4A, 4B, 4C and 4D show aberrations, at the long focal
length extremity, of the lens arrangement shown in FIG. 1;
[0040] FIG. 5 is a lens arrangement of the zoom lens system
according to a second embodiment of the present invention;
[0041] FIGS. 6A, 6B, 6C and 6D show aberrations, at the short focal
length extremity, of the lens construction shown in FIG. 5;
[0042] FIGS. 7A, 7B, 7C and 7D show aberrations, at an intermediate
focal length, of the lens arrangement shown in FIG. 5;
[0043] FIGS. 8A, 8B, 8C and 8D show aberrations, at the long focal
length extremity, of the lens arrangement shown in FIG. 5;
[0044] FIG. 9 is a lens arrangement the zoom lens system according
to a third embodiment the present invention;
[0045] FIGS. 10A, 10B, 10C and 10D show aberrations, at the short
focal length extremity, of the lens arrangement shown in FIG.
9;
[0046] FIGS. 11A, 11B, 11C and 11D show aberrations, at an
intermediate focal length, of the lens arrangement shown in FIG.
9;
[0047] FIGS. 12A, 12B, 12C and 12D show aberrations, at the long
focal length extremity, of the lens arrangement shown in FIG. 9;
and
[0048] FIG. 13 shows lens-group moving paths of the zoom lens
system according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0049] The zoom lens system, as shown in FIG. 13, includes a
positive first lens group 10, a positive second lens group 20 and a
negative third lens group 30, in this order from the object. Upon
zooming from the short focal length extremity to the long focal
length extremity, all the lens groups monotonously (linearly) move
towards the object, while the distance between the first lens group
10 and the second lens group 20 increases, and the distance between
the second lens group 20 and the third lens group 30 decreases. If
the positive first lens group 10 and the positive second lens group
20 are considered to be a positive front lens group, the
relationship between this positive front lens group and the
negative third lens group (rear lens group) 30 can be classified as
a telephoto-type zoom lens system. The aperture stop S is provided
between the second lens group 20 and the third lens group 30, and
moves together with the second lens group 20.
[0050] Condition (1) specifies the change in the distance between
the first lens group 10 and the second lens group 20 from the short
focal length extremity to the long focal length extremity. By
changing the traveling distances of the first and second lens
groups so that condition (1) is satisfied, field curvature can be
corrected over the entire zooming range, and a higher zoom rati can
be attained.
[0051] If (d.sub.T12-d.sub.W12)/f.sub.W exceeds upper limit of
condition (1), the change in the distance between the first and
second lens groups becomes large, so that miniaturization cannot be
attained.
[0052] If (d.sub.T12-d.sub.W12)/f.sub.W exceeds lower limit of
condition (1), field curvature cannot be corrected sufficiently, so
that a higher zoom ration cannot be obtained.
[0053] Condition (2) specifies the combined focal length of the
first lens group 10 and the second lens group 20. By satisfying
this condition, the traveling distances of the first and second
lens groups can be reduced, so that miniaturization of the lens
system can be attained.
[0054] If f.sub.T/f.sub.12T exceeds upper limit of condition (2),
the power of the first lens group 10 and that of the second lens
group 20 become too strong, thereby aberrations occurred therein
are increased. As a result, fluctuations of aberrations upon
zooming become large.
[0055] If f.sub.T/f.sup.12T exceeds lower limit of condition (2),
the traveling distances of the first lens group 10 and the second
lens group 20 become long, so that miniaturization cannot be
attained.
[0056] Condition (3) specifies the focal length of the negative
third lens group 30. By satisfying this condition, the traveling
distance of the third lens group 30 can be made short, thereby
miniaturization of the zoom lens system can be attained.
[0057] If f.sub.T/.vertline.f.sub.3G.vertline. exceeds the upper
limit of condition (3), the power of the third lens group 30
becomes too strong, thereby aberrations occurred in the third lens
group 30 increase. As a result, fluctuations of aberrations upon
zooming become large.
[0058] If f.sub.T/.vertline.f.sub.3G.vertline. exceeds the lower
limit of condition (3), the traveling distance of the third lens
group 30 becomes long, thereby miniaturization of the zoom lens
system cannot be attained.
[0059] Condition (4) specifies the distance between the first lens
group 10 and the second lens group 20 at the long focal length
extremity. By satisfying this condition, mainly field curvature can
be corrected, while the overall length of the zoom lens system at
the long focal length extremity is reduced.
[0060] If d.sub.T12/f.sub.W exceeds the upper limit of condition
(4), the distance between the first lens group 10 and the second
lens group 20 increases, thereby miniaturization of the zoom lens
system cannot be achieved.
[0061] If d.sub.T12/f.sub.W exceeds the lower limit of condition
(4), field curvature, in particular, at the long focal length
extremity cannot be sufficiently corrected.
[0062] Condition (5) specifies the radius of curvature of the
most-object side surface of the positive first lens group 10. By
satisfying this condition and forming the most-object side surface
as a diverging surface (i.e., concave surface), the amount of
peripheral illumination at the short focal length extremity can
suitably be maintained. Accordingly, compared with a convex
surface, an increase of the diameter of the front lens group can be
prevented.
[0063] If r1/f.sub.W exceeds the upper limit of condition (5), the
radius of curvature of the most-object side surface of the first
lens group 10 becomes too small, thereby manufacture thereof is
difficult.
[0064] If r1/f.sub.W exceeds the lower limit of condition (5), a
divergent effect of the most-object side surface cannot be
obtained, and peripheral illumination becomes insufficient.
[0065] Condition (6) specifies the power of a negative lens element
of the first lens group 10 in the case where the negative lens
element is the most-object side lens element thereof. By satisfying
this condition, aberrations occurred in the first lens group 10 can
be reduced.
[0066] If f.sub.1P/f.sub.W exceeds the upper limit of condition
(6), the effect of the correcting of aberrations by the most-object
side lens element cannot be achieved.
[0067] If f.sub.1P/f.sub.W exceeds the lower limit of condition
(6), aberrations occurred in by the most-object side lens element
become large, and optical sensitivity of the most-object side lens
element is increased.
[0068] Condition (7) specifies the amount of change of the
spherical aberration coefficient due to an aspherical surface in
the case where at least one lens element having at least one
aspherical surface thereon is provided in the positive second lens
group 20. By satisfying this condition, the number of lens elements
constituting the second lens group 20 can be reduced, and spherical
aberration can be corrected at the long focal length extremity in
particular.
[0069] If .DELTA.IASP exceeds the upper limit of condition (7), the
effect of the correcting of spherical aberration by the aspherical
surface is diminished, so that the correcting of aberrations cannot
be sufficiently achieved.
[0070] If .DELTA.IASP exceeds the lower limit of condition (7), the
amount of asphericity becomes large, so that manufacture of the
lens element with the aspherical surface becomes difficult.
[0071] Condition (8) specifies the amount of change of the
distortion coefficient due to an aspherical surface in the case
where at least one lens element having at least one aspherical
surface thereon is provided in the negative third lens group 30. By
satisfying this condition, the number of lens elements constituting
the thrid lens group 30 can be reduced, and distortion can be
corrected at the short focal length extremity in particular.
[0072] If .DELTA.VASP exceeds the upper limit of condition (8), the
amount of asphericity increases, and manufacture of the lens
element with the aspherical surface becomes difficult.
[0073] If .DELTA.VASP exceeds the lower limit of condition (8), the
effect of the correcting of distortion by the aspherical surface is
diminished, so that the correcting of aberrations cannot be
sufficiently achieved.
[0074] Specific numerical data of the embodiments will be described
hereinafter. In the diagrams of chromatic aberration (axial
chromatic aberration) represented by spherical aberration, the
solid line and the two types of dotted lines respectively indicate
spherical aberrations with respect to the d, g and C lines. Also,
in the diagrams of lateral chromatic aberration, the two type of
dotted lines respectively indicate magnification with respect to
the g and C lines; however, the d line as the base line coincides
with the ordinates. S designates the sagittal image, and M
designates the meridional image. In the tables, Fno designates the
F-number, f designates the focal length of the entire lens system,
W designates the half angle-of-view (.degree.), fB designates the
back focal distance, r designates the radius of curvature, d
designates the lens-element thickness or distance between lens
elements, Nd designates the refractive index at the d-line, and v
designates the Abbe number.
[0075] In addition to the above, an aspherical surface which is
symmetrical with respect to the optical axis is defined as
follows:
x=cy.sup.2/(1+[1-{1+K}c.sup.2y.sup.2].sup.1/2)+A4y.sup.4+A6y.sup.6+A8y.sup-
.8+A10y.sup.10
[0076] wherein:
[0077] x designates a distance from a tangent plane of an
aspherical vertex;
[0078] C designates a curvature of the aspherical vertex (1/R);
[0079] h designates a distance from the optical axis;
[0080] K designates the conic coefficient; and
[0081] A4 designates a fourth-order aspherical coefficient;
[0082] A6 designates a sixth-order aspherical coefficient;
[0083] A8 designates a eighth-order aspherical coefficient; and
[0084] A10 designates a tenth-order aspherical coefficient.
[0085] [Embodiment 1]
[0086] FIGS. 1 through 4D show the first embodiment of the zoom
lens system. According to the lens arrangement of the first
embodiment shown in FIG. 1, the first lens group 10 includes a
first lens element 10a having a concave surface facing towards the
object, and a positive second lens element 10b, in this order from
the object. The second lens group 20 includes cemented lens
elements having a negative lens element and a positive lens
element, cemented lens elements having a positive lens element and
a negative lens element, and a positive lens element having an
aspherical surface on the image-side surface (a lens element having
at least one aspherical surface), in this order from the object.
The third lens group 30 includes a positive lens element having an
aspherical surface on the object-side surface, and a negative lens
element, in this order from the object. By constituting the first
lens group 10 with a negative first lens element 10a and a positive
second lens element lob, in this order from the object, the
thickness of the first lens group 10 can be reduced, so that the
front-to-back length of a camera can be reduced.
[0087] FIGS. 2A, through 2D show aberrations of the zoom lens
system at the short focal length extremity; FIGS. 3A through 3D
show aberrations of the zoom lens system at an intermediate focal
length; and FIGS. 4A through 4D show aberrations of the zoom lens
system at the long focal length extremity. The aperture stop S is
positioned 0.75 mm toward the image from the surface No. Table 1
shows the numerical data of the first embodiment.
1 TABLE 1 F.sub.NO = 3.8-6.0-12.8 f = 29.00-50.00-120.00 (zoom
ratio: 4.14) W = 36.3-22.9-10.1 f.sub.B = 8.27-26.62-82.42 Surface
No. r d Nd .nu. 1 -65.396 1.50 1.84600 23.8 2 -129.762 0.10 -- -- 3
209.037 2.40 1.60000 52.8 4 -58.221 2.29-9.57-22.29 -- -- 5 -18.907
1.51 1.83481 42.7 6 12.706 4.94 1.79808 25.8 7 -99.121 0.35 -- -- 8
19.932 4.13 1.48749 70.2 9 -11.217 2.00 1.84666 23.8 10 -59.077
1.19 -- -- 11 51.750 2.83 1.73077 40.5 12* -16.950 13.01-7.10-1.91
-- -- 13* -68.356 2.85 1.58547 29.9 14 -24.870 3.98 -- -- 15
-10.899 1.40 1.69000 56.3 16 185.621 -- -- -- *designates the
aspherical surface which is rotationally symmetrical with respect
to the optical axis.
[0088] Aspherical surface data (the aspherical surface coefficients
not indicated are zero (0.00)):
2 Surf. No. K A4 A6 A8 12 0.00 0.5762 .times. 10.sup.-4 -0.7034
.times. 10.sup.-7 0.1383 .times. 10.sup.-8 13 0.00 0.5776 .times.
10.sup.-4 -0.5696 .times. 10.sup.-7 0.3428 .times. 10.sup.-8
[0089] [Embodiment 2]
[0090] FIGS. 5 through 8D show the second embodiment of the zoom
lens system. FIG. 5 shows the lens arrangement of the second
embodiment. FIGS. 6A, through 6D show aberrations of the zoom lens
system at the short focal length extremity; FIGS. 7A through 7D
show aberrations of the zoom lens system at an intermediate focal
length; and FIGS. 8A through 8D show aberrations of the zoom lens
system at the long focal length extremity. The aperture stop S is
positioned 0.75 mm toward the image from the surface No. 12. Table
2 shows the numerical data of the second embodiment. The basic lens
arrangement of the second embodiment is the same as the first
embodiment.
3 TABLE 2 F.sub.NO = 3.8-6.0-13.5 f = 29.00-50.00-125.00 (zoom
ratio: 4.31) W = 36.1-22.9-9.7 f.sub.B = 8.28-26.78-86.97 Surface
No. r d Nd .nu. 1 -65.762 1.50 1.84600 23.8 2 -146.939 1.10 -- -- 3
224.927 2.44 1.60043 46.4 4 -54.517 2.29-9.67-23.15 -- -- 5 -18.589
1.72 1.83481 42.7 6 13.719 4.69 1.80704 25.4 7 -98.032 0.35 -- -- 8
20.155 4.22 1.48749 70.2 9 -11.215 2.00 1.84666 23.8 10 -59.552
1.19 -- -- 11 51.750 2.83 1.73077 40.5 12* -16.950 13.31-7.32-1.89
-- -- 13* -68.020 2.89 1.58547 29.9 14 -24.034 3.79 -- -- 15
-11.133 1.40 1.69000 56.3 16 131.238 -- -- -- *designates the
aspherical surface which is rotationally symmetrical with respect
to the optical axis.
[0091] Aspherical surface data (the aspherical surface coefficients
not indicated are zero (0.00)):
4 Surf. No. K A4 A6 A8 12 0.00 0.5762 .times. 10.sup.-4 -0.7034
.times. 10.sup.-7 0.1383 .times. 10.sup.-8 13 0.00 0.5441 .times.
10.sup.-4 -0.4473 .times. 10.sup.-7 0.2819 .times. 10.sup.-8
[0092] [Embodiment 3]
[0093] FIGS. 9 through 12D show the third embodiment of the zoom
lens system. FIG. 9 shows the lens arrangement of the third
embodiment. FIGS. 10A, through 10D show aberrations of the zoom
lens system at the short focal length extremity; FIGS. 11A through
11D show aberrations of the zoom lens system at an intermediate
focal length; and FIGS. 12A through 12D show aberrations of the
zoom lens system at the long focal length extremity. The aperture
stop S is positioned 0.75 mm toward the image from the surface No.
12. Table 3 shows the numerical data of the third embodiment. The
basic lens arrangement of the second embodiment is the same as the
first embodiment.
5 TABLE 3 F.sub.NO = 3.8-6.0-12.5 f = 29.00-50.00-115.00 (zoom
ratio: 3.97) W = 36.3-22.9-10.5 f.sub.B = 8.27-26.63-78.74 Surface
No. r d Nd .nu. 1 -65.341 1.50 1.84600 23.8 2 -131.137 0.10 -- -- 3
216.503 2.40 1.60000 53.2 4 -57.771 2.29-9.57-21.65 -- -- 5 -18.868
1.60 1.83481 42.7 6 13.015 4.88 1.80168 25.6 7 -99.320 0.35 -- -- 8
19.929 4.13 1.48749 70.2 9 -11.188 2.00 1.84666 23.8 10 -59.256
1.18 -- -- 11 51.750 2.83 1.73077 40.5 12* -16.950 12.99-7.09-2.09
-- -- 13* -69.112 2.83 1.58547 29.9 14 -25.019 3.99 -- -- 15
-10.896 1.40 1.69000 56.3 16 185.421 -- -- -- *designates the
aspherical surface which is rotationally symmetrical with respect
to the optical axis.
[0094] Aspherical surface data (the aspherical surface coefficients
not indicated are zero (0.00)):
6 Surf. No. K A4 A6 A8 12 0.00 0.5762 .times. 10.sup.-4 -0.7034
.times. 10.sup.-7 0.1383 .times. 10.sup.-8 13 0.00 0.5740 .times.
10.sup.-4 -0.4367 .times. 10.sup.-7 0.3292 .times. 10.sup.-8
[0095] The numerical values of each condition of each embodiment
are shown in Table 4.
7 TABLE 4 Embod. 1 Embod. 2 Embod. 3 Cond. (1) 0.69 0.72 0.67 Cond.
(2) 5.01 5.18 4.84 Cond. (3) 5.85 6.03 5.61 Cond. (4) 0.77 0.80
0.75 Cond. (5) -2.26 -2.27 -2.25 Cond. (6) -5.43 -4.89 -5.36
[0096] As can be understood from Table 4, each embodiment satisfied
each condition. Furthermore, as can be understood from the
aberration diagrams, the aberrations of each embodiment are
adequately corrected.
[0097] According to the above description, a small three-lens-group
zoom lens system of telephoto type which has a zoom ratio of about
4.0, and has the half angle of view at the short focal length
extremity is more than 35.degree. can be achieved.
* * * * *