U.S. patent application number 09/769458 was filed with the patent office on 2001-09-06 for zoom lens system.
This patent application is currently assigned to ASAHI KOGAKU KOGYO KABUSHIKI KAISHA. Invention is credited to Enomoto, Takashi, Ishii, Shinichiro, Ito, Takayuki, Nomura, Hiroshi.
Application Number | 20010019457 09/769458 |
Document ID | / |
Family ID | 18546549 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010019457 |
Kind Code |
A1 |
Enomoto, Takashi ; et
al. |
September 6, 2001 |
Zoom lens system
Abstract
In a short-focal-length side zooming range, a moveable sub-lens
group of a zoom lens system is made stationary at one of the
object-side and the image-side end. At the intermediate switching
focal length, the moveable sub-lens group is moved to the other of
the object-side and the image-side end. In a long-focal-length side
zooming range, the moveable sub-lens group is made stationary at
the other end, and the zoom lens system satisfies the following
condition: mNt-mNw<0 (1) wherein mNt designates the transverse
magnification of the most image-plane side lens group of the zoom
lens system when the moveable sub-lens group is at one end; and mNw
designates the transverse magnification of the most image-plane
side lens group of the zoom lens system when the moveable sub-lens
group is at the other end
Inventors: |
Enomoto, Takashi; (Chiba,
JP) ; Nomura, Hiroshi; (Saitama, JP) ; Ito,
Takayuki; (Saitama, JP) ; Ishii, Shinichiro;
(Saitama, JP) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN
1941 ROLAND CLARKE PLACE
RESTON
VA
20191
|
Assignee: |
ASAHI KOGAKU KOGYO KABUSHIKI
KAISHA
Tokyo
JP
|
Family ID: |
18546549 |
Appl. No.: |
09/769458 |
Filed: |
January 26, 2001 |
Current U.S.
Class: |
359/695 ;
359/676; 359/684; 359/693; 359/694 |
Current CPC
Class: |
G02B 15/1421 20190801;
G02B 15/143103 20190801; G02B 15/142 20190801 |
Class at
Publication: |
359/695 ;
359/694; 359/693; 359/676; 359/684 |
International
Class: |
G02B 015/14; G02B
015/22 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 28, 2000 |
JP |
2000-19916 (P) |
Claims
What is claimed is:
1. A zoom lens system comprising a plurality of zooming lens groups
which are relatively moveable in order to vary the focal length of
said zoom lens system, wherein among said plural zooming lens
groups, a predetermined zooming lens group which comprises a
switching lens group comprising at least two sub-lens groups;
wherein one of said sub-lens groups of said switching lens group is
made moveable, with respect to other sub-lens groups, to either an
object-side end or an image-side end; wherein in a
short-focal-length side zooming range from the short focal length
extremity to an intermediate switching focal length, said plural
zooming lens groups and said predetermined zooming lens group are
moved towards said object, while distances among said zooming lens
groups are varied, and while said moveable sub-lens group of said
predetermined zooming lens group is being made stationary at one of
said object-side end and said image-side end; wherein at said
intermediate switching focal length, said moveable sub-lens group
is moved to the other of said object-side end and said image-side
end, and each of plural zooming lens groups and said predetermined
zooming lens group are moved towards the image plane; wherein in a
long-focal-length side zooming range from said intermediate
switching focal length to the long focal length extremity, said
plural zooming lens groups and said predetermined zooming lens
group are moved towards said object, while distances among said
zooming lens groups are varied, and while said moveable sub-lens
group is being made stationary at said other of said object-side
end and said image-side end; and wherein said zoom lens system
satisfies the following condition: mNt-mNw<0 wherein mNt
designates the transverse magnification, at said intermediate
switching focal length, of the most image-plane-side zooming lens
group among said plural zooming lens groups, under the condition
that said moveable sub-lens group of said switching lens group is
being made stationary at said other of said object-side end and
said image-side end; and mNw designates the transverse
magnification, at said intermediate switching focal length, of the
most image-plane-side zooming lens group among said plural zooming
lens group, under the condition that said moveable sub-lens group
of said switching lens group is being made stationary at said one
of said object-side end and said image-side end.
2. The zoom lens system according to claim 1, wherein the most
object-side zooming lens group comprises said switching lens group,
and said zoom lens system satisfies the following condition:
0<(log Z1/log Z)<0.2 wherein Z=ft/fw; Z1=f1t/f1w; fw
designates the focal length of the entire the zoom lens system at
the short focal length extremity; ft designates the focal length of
the entire the zoom lens system at the long focal length extremity;
f1w designates the focal length of a first lens group in said
short-focal-length side zooming range; and f1t designates the focal
length of said first lens group in said long-focal-length side
zooming range.
3. The zoom lens system according to claim 1, wherein at least one
zooming lens group is provided on the object side of said switching
lens group, and said zoom lens system satisfies the following
condition: 0<(log Zi/log Z)-(log Zi'/log Z')<0.2 wherein
Zi=mit/miw; Z'=ft'/fw Zi'=mit'/miw; ft'designates the focal length
of the entire the zoom lens system, at the long focal length
extremity, when said moveable sub-lens group is being made
stationary at said one of said object-side end and said image-side
end; miw designates the transverse magnification of said switching
lens group at the short focal length extremity; mit designates the
transverse magnification of said switching lens group at the long
focal length extremity; and mit' designates the transverse
magnification of said switching lens group at the long focal length
extremity, when said moveable sub-lens group is being made
stationary at said one of said object-side end and said image-side
end.
4. The zoom lens system according to claim 1, satisfying the
following condition: 0.01<.DELTA.di/fw<0.3 wherein .DELTA.di
designates the traveling distance of said moveable sub-lens group
at said intermediate switching focal length.
5. The zoom lens system according to claim 1, wherein said
switching lens group comprises said moveable sub-lens group and
another sub-lens group, and wherein the power of said moveable
sub-lens group is one of negative and positive, and the power of
said another sub-lens group is the other of negative and
positive.
6. The zoom lens system according to claim 1, wherein said
switching lens group comprises a negative sub-lens group and a
positive sub-lens group, in this order from said object, and
wherein said negative sub-lens group comprises said moveable
sub-lens group.
7. The zoom lens system according to claim 2, wherein said zooming
lens groups comprise two lens groups.
8. The zoom lens system according to claim 3, wherein said zooming
lens groups comprise at least three lens groups.
9. The zoom lens system according to claim 2, satisfying the
following condition: 0.01<.DELTA.di/fw<0.3 wherein .DELTA.di
designates the traveling distance of said moveable sub-lens group
at said intermediate switching focal length.
10. The zoom lens system according to claim 3, satisfying the
following condition: 0.01<.DELTA.di/fw<0.3 wherein .DELTA.di
designates the traveling distance of said moveable sub-lens group
at said intermediate switching focal length.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a zoom lens system.
[0003] 2. Description of the Related Art
[0004] In a zoom lens system, a requirement for a high zoom ratio
and a requirement for miniaturization are not compatible. For
example, in a zoom lens system of two-lens-group arrangement which
can be miniaturized, if lens-group moving paths are designed, i.e.
a solution of the lens-group moving path is obtained, with the aim
of obtaining a high zoom ratio, lens groups come into contact with
each other at the long focal length extremity, or lens groups and
the image plane cause interference therebetween at the short focal
length extremity. On the other hand, in the case of a zoom lens
system of three-lens-group arrangement, the zoom ratio can be made
higher than that of a two-lens-group zoom lens system; however,
miniaturization of the zoom lens system is difficult. Furthermore,
if the optical power (hereinafter, power) of each lens group is
determined to obtain an even higher zoom ratio, error sensitivity
of each lens group becomes too high, so that a mechanism which can
maintain necessary precision on the operations of the lens system
under such a high sensitivity is not practical to be obtained.
SUMMARY OF THE INVENTION
[0005] It is an object of the present invention to provide a
miniaturized zoom lens system having a high zoom ratio.
[0006] In order to achieve the above-mentioned object, there is
provided a zoom lens system including relatively moveable more than
two zooming lens groups (hereinafter, N zooming lens groups; N 2)
in order to vary the focal length. Among the N zooming lens groups,
an i-th (i 1, counted from the most object-side zooming lens group)
zooming lens group is a switching lens group (predetermined zooming
lens group) The switching lens group includes more than two
sub-lens groups, and one sub-lens group is made moveable, with
respect to other sub-lens groups, to either the object-side end or
the image-side end.
[0007] In a short-focal-length side zooming range from the short
focal length extremity to an intermediate switching focal length,
the N zooming lens groups and the i-th zooming lens group are moved
towards the object, while (i) distances among the lens groups are
varied, and (ii) the moveable sub-lens group is being made
stationary at one of the object-side end and the image-side
end.
[0008] At the intermediate switching focal length, the moveable
sub-lens group is moved to the other of the object-side end and the
image-side end, and each of the N zooming lens groups and the i-th
zooming lens group are moved towards the image plane.
[0009] In a long-focal-length side zooming range from the
intermediate switching focal length to the long focal length
extremity, the N zooming lens groups and the i-th zooming lens
group are moved towards the object, while (i) distances among the
zooming lens groups are varied, (ii) the moveable sub-lens group is
being made stationary at the other end, and (iii) the zoom lens
system satisfies the following condition:
mNt-mNw<0 (1)
[0010] wherein
[0011] mNt designates the transverse magnification of the N-th,
i.e., the most image-plane side, zooming lens group at the
intermediate switching focal length, under the condition that the
moveable sub-lens group of the switching lens group is being made
stationary at the other end; and
[0012] mNw designates the transverse magnification of the N-th,
i.e., the most image-plane side, zooming lens group at the
intermediate switching focal length, under the condition that the
moveable sub-lens group of the switching lens group is being made
stationary at the one end.
[0013] The most object-side zooming lens group can be formed as the
switching lens group (i=1). In this case, the zoom lens system
preferably satisfies the following condition:
0<(log Z1/log Z)<0.2 (2)
[0014] wherein
[0015] Z=ft/fw;
[0016] Z1=f1t/f1w;
[0017] fw designates the focal length of the entire the zoom lens
system at the short focal length extremity;
[0018] ft designates the focal length of the entire the zoom lens
system at the long focal length extremity;
[0019] f1w designates the focal length of the first lens group in
the short-focal-length side zooming range; and
[0020] f1t designates the focal length of the first lens group in
the long-focal-length side zooming range.
[0021] Furthermore, at least one zooming lens group can be provided
on the object side of the switching lens group (i 2). In this case,
the zoom lens system preferably satisfies the following
condition:
0<(log Zi/log Z)-(log Zi'/log Z')<0.2 (2')
[0022] wherein
[0023] Zi=mit/miw;
[0024] Z'=ft'/fw
[0025] Zi'=mit'/miw;
[0026] ft' designates the focal length of the entire the zoom lens
system, at the long focal length extremity, when the moveable
sub-lens group is being made stationary at the one end;
[0027] miw designates the transverse magnification of the switching
lens group at the short focal length extremity;
[0028] mit designates the transverse magnification of the switching
lens group at the long focal length extremity; and
[0029] mit' designates the transverse magnification of the
switching lens group at the long focal length extremity, when the
moveable sub-lens group is being made stationary at the one
end.
[0030] The zoom lens system according to the present invention can
satisfy the following condition:
0.01<.DELTA.di/fw<0.3 (3)
[0031] wherein
[0032] .DELTA.di designates the traveling distance of the moveable
sub-lens group at the intermediate switching focal length.
[0033] Still further, the switching lens group can be formed as a
two-lens-group arrangement which is constituted by the moveable
sub-lens group and another sub-lens group. In this case, the power
of one lens group is preferably different from the other, e.g., if
the power of the moveable sub-lens group is positive, the power of
the other sub-lens group is negative, and vice versa.
[0034] The switching lens group can include a negative lens group
and a positive lens group, in this order from the object. In this
case, it is preferable that the negative lens group be the moveable
sub-lens group.
[0035] The present disclosure relates to subject matter contained
in Japanese Patent Application No. 2000-019916 (filed on Jan. 28,
2000) which is expressly incorporated herein by reference in its
entirety.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] The invention will be discussed below in detail with
reference to the accompanying drawings, in which:
[0037] FIG. 1 shows a schematic drawing of lens-group moving paths
in a zoom lens system according to a first embodiment of the
present invention;
[0038] FIG. 2A is a drawing for explaining conditions (2) and (3)
applied to the zoom lens system shown in FIG. 1;
[0039] FIG. 2B shows a comparative example with respect to FIG.
2A;
[0040] FIG. 3 shows a schematic drawing of lens-group moving paths
in the zoom lens system according to a second embodiment of the
present invention;
[0041] FIG. 4A is a drawing for explaining conditions (2') and (3)
applied to the zoom lens system shown in FIG. 3;
[0042] FIG. 4B shows a comparative example with respect to FIG.
4A;
[0043] FIG. 5 shows an example of stopping positions of the lens
groups when a photographic operation is carried out;
[0044] FIG. 6 shows an example of the stopping positions of the
lens groups, and an example of actual moving-paths thereof; and
[0045] FIG. 7 shows a schematic drawing of lens-group moving paths
for zooming in the zoom lens system according to a third embodiment
of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] FIG. 1 shows the first embodiment of the zoom lens system.
The zoom lens system includes a positive first zooming lens group
10 (predetermined zooming lens group; switching lens group), and a
negative second zooming lens group 20, in this order from the
object. The first zooming lens group 10 includes a negative first
lens group L1 (first sub-lens group S1) and a positive second lens
group L2 (second sub-lens group S2), in this order from the object.
The second zooming lens group 20 includes a negative third lens
group L3. The second sub-lens group S2 of the first zooming lens
group 10 is fixed in a first zooming-lens-group frame 11. The first
sub-lens group S is mounted on a moveable sub-lens-group frame 12.
The moveable sub-lens group frame 12 is made moveable in the
optical axis direction, by a predetermined distance, along a guide
groove 13 which is formed on the first zooming-lens-group frame 11.
The first sub-lens group S is alternatively moved to either the
object-side extremity at which the moveable sub-lens group frame 12
comes into contact with the front end of the guide groove 13, or
the image-plane-side extremity at which the moveable sub-lens group
frame 12 comes into contact with the rear end of the guide groove
13 (i=1). The third lens group L3 is fixed in a second
zooming-lens-group frame 21. The diaphragm D moves together with
the first zooming lens group 10 (first zooming-lens-group frame
11).
[0047] The lens-group-moving paths according to the first
embodiment enable the first zooming lens group 10 (first
zooming-lens-group frame 11) and the second zooming lens group 20
(second zooming-lens-group frame 21) to move, and also enable the
moveable sub-lens group frame 12 (first sub-lens group S1) to move
along the guide groove 13; and these lens-group-moving paths are
determined as follows:
[0048] [A] In the short-focal-length side zooming range Zw from the
short focal length extremity fw to the intermediate switching focal
length fm, the first sub-lens group S1 maintains a distance d1 (the
first distance: a longer distance) with respect to the second
sub-lens group S2; and the first zooming lens group 10 (first
zooming lens group frame 11) and the second zooming lens group 20
(second zooming-lens-group frame 21) are arranged to move towards
the object while the distance therebetween is varied;
[0049] [B] At the intermediate switching focal length fm, the first
zooming lens group 10 (first zooming-lens-group frame 11) and the
second zooming lens group 20 (second zooming-lens-group frame 21)
move towards the image plane with respect to the long-focal-length
side extremity of the short-focal-length side zooming range Zw; and
the first sub-lens group S1 moves to the image-plane-side extremity
of the guide groove 13, thereby the distance d1 between the first
sub-lens group S1 and the second sub-lens group S2 is made shorter
to form a shorter distance d2 (the second distance: a shorter
distance); and
[0050] [C] In the long-focal-length side zooming range Zt from the
intermediate switching focal length fin to the long focal length
extremity ft, the first sub-lens group S1 maintains the shorter
distance d2 with respect to the second sub-lens group S2; and the
first zooming lens group 10 (first zooming-lens-group frame 11) and
the second zooming lens group 20 (second zooming-lens-group frame
21) move towards the object with respect to the positions thereof
which are determined, at the intermediate switching focal length
fm, after the zooming lens groups are moved towards the image
plane, while the distance between the first and second zooming lens
groups is varied.
[0051] The lens-group-moving paths for the first zooming lens group
10 (first zooming-lens-group frame 11) and the second zooming lens
group 20 (second zooming-lens-group frame 21) are simply depicted
as straight lines in FIG. 1. It should however be noted that actual
lens-group-moving paths are not necessarily straight lines.
[0052] Focusing is performed by integrally moving the first
sub-lens group S1 and the second sub-lens group S2, i.e., the first
zooming lens group 10 (first zooming-lens-group frame 11)
regardless of the zooming ranges.
[0053] The lens-group-moving paths have discontinuities at the
intermediate switching focal length fm; however, by adequately
determining the positions of the first sub-lens group S1 (first
lens group L1), the second sub-lens group S2 (second lens group L2)
and the third lens group L3 respectively at the short focal length
extremity fw, the intermediate switching focal length fin
(discontinuity) and the long focal length extremity ft, solutions
by which an image is correctly formed can be obtained. According to
the lens-group-moving paths with these solutions, a zoom lens
system which is miniaturized and has a high zoom ratio can be
obtained.
[0054] The existence of solutions for the lens-group-moving paths
of the first embodiment can be explained by, for example, the
following discussions:
[0055] The zoom lens system of the first embodiment can be divided
into a negative lens group, a positive lens group, and a negative
lens group, in this order from the object. Here, the negative and
the positive lens groups on the object side (i.e., the first
sub-lens group S1 and the second sub lens group S2) are considered
to be a positive front lens group (the first zooming lens group 10)
in which the relative position of the negative and positive lens
groups is fixed respectively at the long focal length extremity ft
and at the short focal length extremity fw. Since the distance
between the first sub-lens group S1 and the second sub-lens group
S2 is longer at the short focal length extremity fw than at the
long focal length extremity ft (d1>d2), the focal length Pt of
the first zooming lens group 10 at the long focal length extremity
ft is longer than the focal length Pw thereof at the short focal
length extremity fw, i.e., Pt>Pw. In other words, the first
zooming lens group 10 with the focal length Pt and the second
zooming lens group 20 can be considered to be a two-lens-group zoom
lens system, and the first zooming lens group 10 with the focal
length Pw and the second zooming lens group 20 can be considered to
be another two-lens group zoom lens system. Therefore solutions for
each zoom lens system can be obtained. More concretely, one of the
two solutions is the lens-group-moving paths in the
short-focal-length side zooming range Zw, and the other solution is
the lens-group-moving paths in the long-focal-length side zooming
range Zt. However, at the intermediate switching focal length fm,
these paths are discontinued, and the distance between the negative
and the positive lens groups in the front lens group is not the
same. It should be understood that though the movement of the lens
groups upon zooming is substantially the same as that of a
two-lens-group zoom lens system, a miniaturized zoom lens system
with a high zoom ratio can be obtained by (i) providing the
discontinuities along the lens-group-moving paths for the first
zooming lens group 10 and the second zooming lens group 20 at the
intermediate switching focal length fm, and (ii) by varying the
distance between the negative and the positive lens groups in the
first zooming lens group 10. The above is discussed for the first
embodiment; however, the discussions are also applicable for other
embodiments by replacing the term of two-lens-group zoom lens
system with that of the N-lens-group zoom lens system (N:3 or
more).
[0056] It is emphasized that, because of the aforementioned
discontinuities and varying of distances, the disclosed invention
does not fit within the ordinary meaning of an "N lens group"
system. That is, the inventive employment of the "switching lens
group" removes the disclosed invention from the ordinary "N lens
group" definitions of the art (e.g., "two lens group", "three lens
group", "four lens group" systems, etc.).
[0057] For example, in the case of a lens having a switching lens
group and one "conventional" lens group (such as the first
embodiment), the present disclosure characterizes, for the purposes
of explanation, such a lens both (i) as having three lens groups
L1, L2, and L3, and (i) as having a first zooming lens group 10
(with first and second sub-lens groups S1 and S2) and a second
zooming lens group 20. However, the use of the two different
characterizations does not indicate that the system according to
the invention should be considered to be either one of, in this
case, a conventional "three lens group" system or a conventional
"two lens group" system. Instead, the use of two different
characterizations emphasizes that the inventive system should be
considered to be outside the ordinary meaning of, in this case,
either term "two lens group" or "three lens group." The same
principle applies to a lens having two, three, or more
"conventional" lens groups in combination with the switching lens
group.
[0058] Accordingly, the claims and disclosure of the present
application should be interpreted to be consistent with the meaning
of "lens group"; "sub-lens group"; "switching lens group"; and
"zooming lens group" as set forth herein, rather than interpreted
to be consistent with definitions of "lens group" or "N lens group"
as ordinarily known and employed in the art.
[0059] In the zoom lens system of the first embodiment, at the
intermediate switching focal length fm, by varying the distance
between the first sub-lens group S1 and the second sub-lens group
S2, and at the same time, by appropriately moving the zooming lens
groups, each lens group can be moved to satisfy condition (1) so
that the second zooming lens group 20, i.e., the most-image side
zooming lens group, can have two transverse magnifications at the
intermediate switching focal length fm.
[0060] Condition (1) is obtained as follows:
[0061] First, the following relation is obtained with respect to
the intermediate switching focal length fm:
fm=Pt.times.mNt=Pw.times.mNw
[0062] Here, as explained, Pt>Pw, mNt<mNw, then "mNt-mNw
<0", i.e., condition (1) is obtained.
[0063] By satisfying condition (1) at the intermediate switching
focal length fm, a miniaturized zoom lens system with a high zoom
ratio can be achieved, while (i) the power of each lens group is
not excessively increased, and (ii) the distances among lens
groups, and the distance between the most image-side lens group and
the image plane are determined so that the lens groups can be moved
by a predetermined mechanism to obtain these distances.
[0064] If mNt-mNw exceeds the upper limit of condition (1), in
other words, if mNt-mNw=0 (no change in the magnification) or
mNt-mNw>0, the former (mNt-mNw=0) indicates a conventional zoom
lens system in which only one state is provided with respect to the
intermediate switching focal length fm; and the latter
(mNt-mNw>0) causes (i) interference between the most image-side
lens group and the image plane, at the short focal length extremity
where the back focal distance is short, and (ii) lens groups come
into contact with each other at the long focal length extremity
where lens groups come closer to each other. Due to these factors,
a high zoom ratio cannot be obtained. Condition (1) can be applied
not only to a two-lens-group zoom lens system, but also to a zoom
lens system having N lens groups (N: more than 2) thereof.
[0065] FIG. 2A is the drawing for explaining conditions (2) and (3)
applied to the zoom lens system shown in FIG. 1. FIG. 2B shows a
comparative example with respect to FIG. 2A. More concretely, FIG.
2A corresponds to FIG. 1, while FIG. 2B indicates a comparative
example where no switching lens group is provided, i.e., the first
lens group L1 (first sub-lens group S1) and the second lens group
L2 (second sub-lens group S2), which constitute the negative first
zooming lens group 10, are not relatively moveable over the entire
zooming range. Table 1 shows data of the zoom lens system with
respect to the first embodiment and the comparative example.
1TABLE 1 [Embodiment 1] Focal Length First Zooming Lens First
Sub-Lens -32.87 Group Group S1 Second Sub-Lens 16.50 Group S2
Second Zooming Lens -19.62 Group Focal Length of Entire Zoom Lens
System fm = 60 fw = 29 Zw Zt ft = 112 e1 10.12 10.12 7.12 7.12 e2
21.00 13.85 16.02 12.51
[0066] `e1` designates the distance between the second principal
point of the first sub-lens group S1 and the first principal point
of the second sub-lens group S2.
[0067] `e2` designates the distance between the second principal
point of the second sub-lens group S2 and the first principal point
of the second zooming lens group 20.
2 [Comparative Example] The Focal Length of Entire Zoom Lens System
fw = 29 ft' = 74.98 e1 10.12 10.12 e2 21.00 12.51
[0068] In FIGS. 2A and 2B,
[0069] fw designates the focal length of the entire zoom lens
system at the short focal length extremity (fw=29 mm);
[0070] ft designates the focal length of the entire zoom lens
system at the long focal length extremity (ft=112 mm);
[0071] f1w designates the focal length of the first lens group L1
in the short-focal-length side zooming range (f1w=20 mm); and
[0072] f1t designates the focal length of the first lens group L1
in the long-focal-length side zooming range (f1t=23 mm); and
[0073] .DELTA.d designates the traveling distance the moveable
sub-lens group S1 at the intermediate switching focal length fm
((d1w-d1t)=3.0mm).
[0074] Accordingly,
[0075] Z=ft/fw =112/29
[0076] Z1=f1t/f1w=23/20
[0077] LogZ1/log Z=0.09, and thus satisfying condition (2).
[0078] In FIGS. 2A and 2B, (i) the corresponding fist lens groups
L1 (moveable first sub-lens groups S1), the corresponding second
lens groups L2 (second sub-lens groups S2) and the corresponding
third lens group L3 have the identical arrangements and power; and
(ii) the corresponding distances dw, at the short focal length
extremity, between the first zooming lens group 10 and the second
zooming lens group 20 are identical, and so are the corresponding
distances dt at the long focal length extremity.
[0079] In the first embodiment, ft' designates the focal length of
the entire the zoom lens system, at the long focal length
extremity, when the fist lens groups L1 (moveable first sub-lens
groups S1) is being made stationary at the object-side end of the
guide groove 13 (ft'=75mm).
[0080] FIG. 3 shows the second embodiment of the zoom lens system.
The zoom lens system includes a positive first zooming lens group
10, a positive second zooming lens group 20 and a negative third
zooming lens group 30, in this order from the object. The first
zooming lens group 10 includes a positive first lens group L1. The
second zooming lens group 20 (predetermined zooming lens group;
switching lens group) includes a negative second lens group L2
(first sub-lens group S1) and a positive third lens group L3
(second sub-lens group S2), in this order from the object. The
third zooming lens group 30 includes a negative fourth lens group
L4. The first lens group L1 is fixed in a first zooming-lens-group
frame 11. The second sub-lens group S2 of the second zooming lens
group 20 is fixed in a second zooming-lens-group frame 21. The
first sub-lens group S1 is mounted on a moveable sub-lens group
frame 22. The moveable sub-lens group frame 22 is arranged to move,
in the optical axis direction, by a predetermined distance, along a
guide groove 23 which is formed on the second zooming-lens-group
frame 21. The first sub-lens group S1 is alternatively moved to
either the object-side extremity at which the moveable sub-lens
group frame 22 comes into contact with the front end of the guide
groove 23, or the image-plane-side extremity at which the moveable
sub-lens group frame 22 comes into contact with the rear end of the
guide groove 23 (i=2). The fourth lens group L4 is fixed in a third
zooming-lens-group frame 31. The diaphragm D is arranged to move
together with the second zooming lens group 20 (second
zooming-lens-group frame 21).
[0081] The lens-group-moving paths according to the second
embodiment enable the first zooming lens group 10 (first
zooming-lens-group frame 11), the second zooming lens group 20
(second zooming-lens-group frame 21) and the third zooming lens
group 30 (third zooming-lens-group frame 31) to move, and also
enable the moveable sub-lens group frame 22 (first sub-lens group
S1) to move along the guide groove 23; and these lens-group-moving
paths are determined as follows:
[0082] [A] In the short-focal-length side zooming range Zw from the
short focal length extremity fw to the intermediate switching focal
length fm, the first sub-lens group S1 maintains a distance d1 (the
first distance: a longer distance) with respect to the second
sub-lens group S2; and the first zooming lens group 10 (first
zooming lens group frame 11), the second zooming lens group 20
(second zooming-lens-group frame 21) and third zooming lens group
30 (third zooming-lens-group frame 31) are arranged to move towards
the object while the distances therebetween are varied;
[0083] [B] At the intermediate switching focal length fm, the first
zooming lens group 10 (first zooming-lens-group frame 11), the
second zooming lens group 20 (second zooming-lens-group frame 21)
and third zooming lens group 30 (third zooming-lens-group frame 31)
move towards the image plane with respect to the long-focal-length
side extremity of the short-focal-length side zooming range Zw; and
the first sub-lens group S1 moves to the image-plane-side extremity
of the guide groove 23, thereby the distance d1 between the first
sub-lens group S1 and the second sub-lens group S2 is made shorter
to form a shorter distance d2 (the second distance: a shorter
distance); and
[0084] [C] In the long-focal-length side zooming range Zt from the
intermediate switching focal length fin to the long focal length
extremity ft, the first sub-lens group S1 maintains the shorter
distance d2 with respect to the second sub-lens group S2; and the
first zooming lens group 10 (first zooming-lens-group frame 11),
the second zooming lens group 20 (second zooming-lens-group frame
21) and the third zooming lens group 30 (third zooming-lens-group
frame 31) move towards the object with respect to the positions
thereof which are determined, at the intermediate switching focal
length fm, after the lens groups are moved towards the image plane,
while the distances among the first through third lens groups are
varied.
[0085] The lens-group-moving paths for the first zooming lens group
10 (first zooming-lens-group frame 11), the second zooming lens
group 20 (second zooming-lens-group frame 21) and the third zooming
lens group 30 (third zooming-lens-group frame 31) are simply
depicted as straight lines in FIG. 3. It should however be noted
that actual lens-group-moving paths are not necessarily straight
lines.
[0086] Focusing is performed by integrally moving the first
sub-lens group S1 and the second sub-lens group S2, i.e., the
second zooming lens group 20 (second zooming-lens-group frame 21)
regardless of the zooming ranges.
[0087] Similar to the first embodiment, the lens-group-moving paths
have discontinuities at the intermediate switching focal length fm;
however, by adequately determining the positions of the first lens
group L1, the first sub-lens group S1 (second lens group L2), the
second sub-lens group S2 (third lens group L3) and the fourth lens
group L4 respectively at the short focal length extremity fw, the
intermediate switching focal length fin (discontinuity) and the
long focal length extremity ft, solutions by which an image is
correctly formed can be obtained. According to the
lens-group-moving paths with these solutions, a zoom lens system
which is miniaturized and has a high zoom ratio can be
obtained.
[0088] Also, similar to the first embodiment, in the zoom lens
system of the second embodiment, at the intermediate switching
focal length fm, by varying the distance between the first sub-lens
group S1 and the second sub-lens group S2, and at the same time, by
appropriately moving the zooming lens groups, each lens group can
be moved to satisfy condition (1) so that the third zooming lens
group 30, i.e., the most-image side lens group, can have two
transverse magnifications at the intermediate switching focal
length fm.
[0089] FIG. 4A is the drawing for explaining conditions (2') and
(3) applied to the zoom lens system shown in FIG. 3. FIG. 4B shows
a comparative example with respect to FIG. 4A. More concretely,
FIG. 4A corresponds to FIG. 3, while FIG. 4B indicates a
comparative example where no switching lens group is provided,
i.e., the negative second lens group L2 (first sub-lens group S1)
and the positive third lens group L3 (second sub-lens group S2),
which constitute the second zooming lens group 20, are not
relatively moveable over the entire zooming range. Table 2 shows
data of the zoom lens system with respect to the second embodiment
and the comparative example.
3TABLE 2 [Embodiment 2] Focal Length First Zooming Lens Group 68.34
Second Zooming Lens First Sub-Lens -25.38 Group Group S1 Second
Sub-Lens 18.81 Group S2 Third Zooming Lens Group -20.55 Focal
Length of Entire Zoom Lens System fm = 80 fw = 39.4 Zw Zt ft = 160
g1 1.72 10.63 13.72 22.59 g2 7.95 7.95 2.03 2.03 g3 23.70 16.06
19.17 12.17
[0090] `g1` designates the distance between the second principal
point of the first zooming lens group 10 and the first principal
point of the first sub-lens group S1.
[0091] `g2` designates the distance between the second principal
point of the first sub-lens group S1 and the first principal point
of the second sub-lens group S2.
[0092] `g3` designates the distance between the second principal
point of the second sub-lens group S2 and the first principal point
of the third zooming lens group 30.
4 [Comparative Example 2] The Focal Length of Entire Zoom Lens
System fw = 39.4 ft' = 114.3 g1 1.72 22.59 g2 7.95 7.95 g3 23.70
12.17
[0093] In FIGS. 4A and 4B,
[0094] fw designates the focal length of the entire zoom lens
system at the short focal length extremity (fw=39 mm);
[0095] ft designates the focal length of the entire zoom lens
system at the long focal length extremity (ft=160 mm);
[0096] ft' designates the focal length of the entire the zoom lens
system, at the long focal length extremity, when the moveable
sub-lens groups S1 of the switching lens group (second zooming lens
group 20) is being made stationary at the object-side extremity of
the guide groove 23 (ft'=114 mm);
[0097] m2w designates the transverse magnification of the switching
lens group (second zooming lens group 20) at the short focal length
extremity (m2w=0.384);
[0098] m2t designates the transverse magnification of the switching
lens group (second zooming lens group 20) at the long focal length
extremity (m2t=0.583);
[0099] m2t' designates the transverse magnification, at the long
focal length extremity, when the moveable sub-lens groups S1 of the
switching lens group (second zooming lens group 20) is being made
stationary at the object-side extremity of the guide groove 23
(m2t'=0.508);
[0100] .DELTA.d designates the traveling distance the moveable
sub-lens group S1 at the intermediate switching focal length fm
((d2w-d2t)=5.92 mm).
[0101] Accordingly,
[0102] Z=ft/fw=160/39
[0103] Z2=m2t/m2w=0.583/0.384
[0104] Z'=ft'/fw=114/39
[0105] Z2'=m2t'/m2w=0.508/0.384
[0106] (LogZ2/log Z)-(LogZ2'/log Z')=0.03, and thus satisfying
condition (2').
[0107] Conditions (2) and (2') specify the ratio of the zoom ratio
of the switching lens group according to the switching operation at
the intermediate switching focal length fin to that of the entire
zoom lens system. These conditions are provided for obtaining more
preferable zooming effects on the zoom lens system.
[0108] If (log Z1/log Z) and ((logzi/log Z)-(logzi'/logz')) exceed
the upper limit of conditions (2) and (2'), the traveling distance
of the moveable sub-lens group S1 of the switching lens group
becomes long, so that the diameter and length of the zoom lens
system become large, which causes an increase of the size of the
entire zoom lens system.
[0109] If (log Z1/log Z) and ((logzi/log Z)-(log Zi'/log Z'))
exceed the lower limit of conditions (2) and (2'), zooming effects
of the moveable sub-lens group S1 in the switching lens group is
diminished, thereby a high zoom ratio and miniaturization cannot be
achieved.
[0110] Condition (3) specifies the traveling distance of the
moveable sub-lens group S1 in the switching lens group. By
satisfying this condition, zooming effects due to the moveable
sub-lens group S1 can be obtained, and both a high zoom ratio and
miniaturization of the zoom lens system can be achieved, while the
traveling distance of the moveable sub-lens group S1 in the
switching lens group can be reduced.
[0111] If the traveling distance of the moveable sub-lens group S1
becomes long to the extent that .DELTA.di/fw exceeds the upper
limit of condition (3), the diameter and length of the zoom lens
system become large, so that the size of the entire zoom lens
system has to be increased.
[0112] If the traveling distance of the moveable sub-lens group S1
becomes short to the extent that .DELTA.di/fw exceeds the lower
limit of condition (3), zooming effects due to the moveable
sub-lens group S1 are diminished, so that a high zoom ratio and
miniaturization of the zoom lens system cannot be achieved.
[0113] In the first and second embodiments, the first sub-lens
group S1 is made moveable with respect to the second sub-lens group
S2. In other words, the second sub-lens group S2 is fixed in the
first zooming-lens-group frame 11 or the second zooming-lens-group
frame 21, the first sub-lens group S1 is made moveable with respect
to the first zooming-lens-group frame 11 or the second
zooming-lens-group frame 21. However, this relation can be
reversed, and a reversed arrangement will be explained as the third
embodiment according to FIG. 7 in which the first embodiment is
modified, i.e., the first sub-lens group S1 is fixed in the first
zooming-lens-group frame 11, and the second sub-lens group S2 is
made moveable with respect to the first zooming-lens-group frame
11.
[0114] More concretely, in FIG. 7, the zoom lens system includes
the positive first zooming lens group 10 (predetermined zooming
lens group; switching lens group), and the negative second zooming
lens group 20, in this order from the object. The first zooming
lens group 10 includes the negative first lens group L1 (first
sub-lens group S1) and a positive second lens group L2 (second
sub-lens group S2), in this order from the object. The second
zooming lens group 20 includes a negative third lens group L3. The
first sub-lens group S1 of the first zooming lens group 10 is fixed
in the first zooming-lens-group frame 11. On the other hand, a
second zooming-lens-group frame 12' in which the second sub-lens
group S2 is supported is made moveable in the optical axis
direction, by a predetermined distance, along a guide groove 13'
which is formed on the first zooming-lens-group frame 11. The
second sub-lens group S2 is alternatively moved to either the
object-side extremity at which the moveable sub-lens-group frame
12' comes into contact with the front end of the guide groove 13',
or the image-plane-side extremity at which the moveable sub-lens
group frame 12' comes into contact with the rear end of the guide
groove 13'. The third lens group L3 is fixed in the second
zooming-lens-group frame 21. The diaphragm D moves together with
the first zooming lens group 10 (first zooming-lens-group frame
11).
[0115] The lens-group-moving paths according to the third
embodiment enable the first zooming lens group 10 (first
zooming-lens-group frame 11) and the second zooming lens group 20
(second zooming-lens-group frame 21) to move, and also enable the
moveable sub-lens group frame 12' (second sub-lens group S2) to
move along the guide groove 13'; and these lens-group-moving paths
are determined as follows:
[0116] [A] In the short-focal-length side zooming range Zw from the
short focal length extremity fw to the intermediate switching focal
length fm, the second sub-lens group S2 maintains a distance d1
(the first distance: a longer distance) with respect to the first
sub-lens group S1; and the first zooming lens group 10 (first
zooming lens group frame 11) and the second zooming lens group 20
(second zooming-lens-group frame 21) are arranged to move towards
the object while the distance therebetween is varied;
[0117] [B] At the intermediate switching focal length fm, the first
zooming lens group 10 (first zooming-lens-group frame 11) and the
second zooming lens group 20 (second zooming-lens-group frame 21)
move towards the image plane with respect to the long-focal-length
side extremity of the short-focal-length side zooming range Zw; and
the second sub-lens group S2 moves to the object-side extremity of
the guide groove 13', thereby the distance d1 between the first
sub-lens group S1 and the second sub-lens group S2 is made shorter
to form a shorter distance d2 (the second distance: a shorter
distance); and
[0118] [C] In the long-focal-length side zooming range Zt from the
intermediate switching focal length fin to the long focal length
extremity ft, the second sub-lens group S2 maintains the shorter
distance d2 with respect to the first sub-lens group S1; and the
first zooming lens group 10 (first zooming-lens-group frame 11) and
the second zooming lens group 20 (second zooming-lens-group frame
21) move towards the object with respect to the positions thereof
which are determined, at the intermediate switching focal length
fm, after the lens groups are moved towards the image plane, while
the distance between the first and second lens groups is
varied.
[0119] The discussions in regard to conditions (1) through (3) are
also applicable to the third embodiment shown in FIG. 7.
[0120] It is practical to apply the above-described zoom lens
system to a photographing lens system of a camera in which the
photographing lens system and a finder optical system are
independently provided. Moreover, with respect to each lens group,
positions at which the lens group stops upon zooming are preferably
determined in a stepwise manner along the lens-group-moving path,
i.e., it is preferable to provide a plurality of focal-length
steps. FIGS. 5 and 6 show that positions for stopping each lens
group are determined in a stepwise manner along the
lens-group-moving paths. Since these lens systems shown in FIGS. 5
and 6 are the same as that of the first embodiment, the identical
components are provided with the same numerals. The
lens-group-moving paths are depicted with dotted lines; and
positions at which the first lens group frame 11 and the second
lens group frame 21 are to be stopped are indicated with black dots
along the dotted lines. Further, in FIG. 6, the dots are connected
by smooth curved lines. According to an actual mechanical
structure, the first lens group frame 11 and the second lens group
frame 21 can be moved along such smooth curved lines.
[0121] In the embodiments, each lens group is illustrated as a
single lens element; however, a lens group can of course include a
plurality of lens elements.
[0122] The numerical values of each condition for each embodiment
are shown in Table 3.
5 TABLE 3 Embodiment 1 Embodiment 2 Condition (1) -0.33 -0.54
Condition (2) 0.09 -- Condition (2') -- 0.03 Condition (3) 0.10
0.15
[0123] As can be understood from Table 3, the first embodiment
satisfies conditions (1), (2) and (3); and the second embodiment
satisfies conditions (1), (2') and (3).
[0124] According to the above description, a miniaturized zoom lens
system can be provided wherein a high zoom ratio can be
obtained.
* * * * *