Title: Retracting mechanism of a zoom lens barrel
Abstract: A retracting mechanism of a zoom lens barrel includes a first through third lens group moving rings; a first linear guide projection formed on the first lens group moving ring to be engaged in a linear guide slot from outside the second lens group moving ring, the first linear guide projection including a hanging groove formed therealong, a rear end of the hanging groove being closed; a second linear guide projection formed on the third lens group moving ring to be engaged in the linear guide slot from inside the second lens group moving ring; and a linear moving key projecting from a front end of the second linear guide projection to be engaged in the hanging groove. A rear moving limit of the third lens group moving ring is determined by contact of the linear moving key with the closed end of the hanging groove.
Patent Number: 6,853,500 Issued on 02/08/2005 to Nomura, et al.
| Inventors:
|
Nomura; Hiroshi (Saitama, JP);
Yamazaki; Yoshihiro (Saitama, JP);
Okuda; Isao (Saitama, JP)
|
| Assignee:
|
PENTAX Corporation (Tokyo, JP)
|
| Appl. No.:
|
776238 |
| Filed:
|
February 12, 2004 |
Foreign Application Priority Data
| Feb 13, 2003[JP] | 2003-034959 |
| Current U.S. Class: |
359/695; 359/700; 359/701; 359/702 |
| Intern'l Class: |
G02B 015/14 |
| Field of Search: |
359/694-695,699-702,823
|
References Cited [Referenced By]
U.S. Patent Documents
| 5488513 | Jan., 1996 | Tanaka.
| |
| 5589987 | Dec., 1996 | Tanaka.
| |
| 6469840 | Oct., 2002 | Nomura et al.
| |
| 2003/0007796 | Jan., 2003 | Nomura et al.
| |
| 2004/0042089 | Mar., 2004 | Nomura.
| |
| 2004/0042777 | Mar., 2004 | Nomura.
| |
| 2004/0051971 | Mar., 2004 | Nomura.
| |
| 2004/0156122 | Aug., 2004 | Nomura et al. | 359/694.
|
| 2004/0156123 | Aug., 2004 | Nomura et al. | 359/699.
|
| 2004/0156127 | Aug., 2004 | Nomura et al. | 359/821.
|
| 2004/0156181 | Aug., 2004 | Nomura et al. | 362/18.
|
| 2004/0160678 | Aug., 2004 | Nomura et al. | 359/701.
|
| 2004/0160683 | Aug., 2004 | Nomura et al. | 359/819.
|
| Foreign Patent Documents |
| 10-282394 | Oct., 1998 | JP.
| |
| 2001-215385 | Aug., 2001 | JP.
| |
| 2003-021775 | Jan., 2003 | JP.
| |
Primary Examiner: Mack; Ricky
Attorney, Agent or Firm: Greenblum & Bernstein, P.L.C.
Claims
What is claimed is:
1. A retracting mechanism of a zoom lens barrel including a first lens
group, a second lens group and a third lens group, in that order from an
object side, wherein said first lens group and said third lens group are
integrally moved along an optical axis thereof during a zooming operation,
and wherein at least one of said first lens group and said third lens
group is moved relative to the other to reduce a distance therebetween
when said zoom lens barrel is retracted, said retracting mechanism
comprising:
a first lens group moving ring which is linearly guided along said optical
axis, and supports said first lens group;
a second lens group moving ring which is linearly guided along said optical
axis, and supports said second lens group;
a third lens group moving ring which is linearly guided along said optical
axis, and supports said third lens group, said third lens group moving
ring being allowed to freely approach said first lens group moving ring
while being prevented from moving away from said first lens group moving
ring beyond a moving limit relative to said first lens group moving ring;
a cam mechanism for moving said first lens group moving ring and said
second lens group moving ring in respective moving manners independent of
each other along said optical axis;
a biasing device for biasing said third lens group moving ring in a
direction away from said first lens group moving ring;
a linear guide through-slot formed on said second lens group moving ring to
be elongated in a direction parallel to said optical axis;
a first linear guide projection formed on said first lens group moving ring
to be engaged in said linear guide through-slot from outside said second
lens group moving ring, said first linear guide projection including a
hanging groove formed along a substantially center thereof and elongated
in a direction parallel to said optical axis, a rear end of said hanging
groove being closed;
a second linear guide projection formed on said third lens group moving
ring to be engaged in said linear guide through-slot from inside said
second lens group moving ring; and
a linear moving key projecting from a front end of said second linear guide
projection to be engaged in said hanging groove,
wherein a rear moving limit of said third lens group moving ring relative
to said first lens group moving ring is determined by contact of said
linear moving key with said closed rear end of said hanging groove.
2. The retracting mechanism according to claim 1, wherein said hanging
groove comprises:
a narrow-width groove portion which communicatively connects with said
linear guide through-slot; and
a wide-width groove portion which communicative connects with said
narrow-width groove portion, a width of said wide-width groove portion in
a circumferential direction of said first lens group moving ring being
greater than that of said narrow-width groove portion,
wherein said linear moving key comprises:
a neck portion which is engaged in said narrow-width groove portion; and
a head portion which is engaged in said wide-width groove portion, a width
of said head portion in a circumferential direction of said first lens
group moving ring being greater than that of said neck portion.
3. The retracting mechanism according to claim 1, wherein said second lens
group moving ring comprises:
a follower introducing through-slot which extends orthogonal to said linear
guide through-slot to communicatively connect with said linear
through-guide slot; and
a first follower introducing groove which extends parallel to said optical
axis to communicative connect with said follower introducing through-slot,
a front end of said first follower introducing groove communicatively
connecting with said follower introducing through-slot, a rear end of said
first follower introducing groove being open on a rear surface of said
second lens group moving ring,
wherein said first lens group moving ring comprises a second follower
introducing groove which radially communicatively connects with said
follower introducing through-slot and said hanging groove when said first
lens group moving ring is positioned at a specific position relative to
said second lens group moving ring in said optical axis direction, and
wherein said linear moving key is inserted into said hanging groove via
said follower introducing through-slot, said first follower introducing
groove and said second follower introducing groove during assembly of said
zoom lens barrel.
4. The retracting mechanism according to claim 1, wherein said first lens
group moving ring, said second lens group moving ring and said third lens
group moving ring are coaxially arranged so that said first lens group
moving ring is positioned around said second lens group moving ring, and
so that said second lens group moving ring is positioned around said third
lens group moving ring.
5. The retracting mechanism according to claim 1, wherein said cam
mechanism comprises:
a cam ring which is positioned around said second lens group moving ring to
be rotatable relative to said second lens group moving ring, and includes
a plurality of outer cam grooves formed on an outer peripheral surface of
said cam ring, and a plurality of inner cam grooves formed on an inner
peripheral surface of said cam ring;
a plurality of inward cam followers which project radially inwards from
said first lens group moving ring to be engaged in said plurality of outer
cam grooves, respectively; and
a plurality of outward cam followers which project radially outwards from
said second lens group moving ring to be engaged in said plurality of
inner cam grooves, respectively.
6. The retracting mechanism according to claim 1, wherein said biasing
device comprises a compression coil spring.
7. The retracting mechanism according to claim 5, positions of said first
lens group moving ring and said second lens group moving ring in said
optical axis direction are adjusted by rotating said cam ring to make said
second follower introducing groove and said follower introducing
through-slot aligned in said optical axis direction so that said second
follower introducing grooves, said follower introducing through-slots and
said first follower introducing grooves form an L-shaped follower
introducing channel, through which said linear moving key is inserted into
said hanging groove, when said third lens group moving ring is installed
in said zoom lens barrel during assembly.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a retracting mechanism of a zoom lens
barrel.
2. Description of the Related Art
A zoom lens system including a first lens group, a second lens group and a
third lens group in that order from the object side, wherein the first
lens group and the third lens group are integrally moved along an optical
axis during a variation of a focal length, is known in the art. A
retractable zoom lens barrel including such a type of zoom lens system,
wherein a integral movement relationship between the first lens group and
the third lens group is canceled to bring the first lens group close to
the second and third lens groups to reduce the length of the zoom lens
barrel when it is retracted to a retracted position (full-retracted
position or a power-off position), is also known in the art. In general, a
compression coil spring for biasing the second lens group and the third
lens group in opposite directions away from each other is installed
therebetween so that the third lens group is moved rearward to its rear
moving limit relative to the first lens group by the spring force of the
compression coil spring to establish the aforementioned integral movement
relationship between the first lens group and the third lens group when
the focal length of the zoom lens system is varied (when the zoom lens
barrel is in a ready-to-photograph state), and so that the third lens
group is brought close to the second lens group (and the first lens group)
by compressing the compression coil spring when the zoom lens barrel is
retracted to the retracted position.
Such a conventional zoom lens barrel is usually provided with a moving ring
which supports the third lens group and is guided along the optical axis
of the zoom lens system, and is further provided between the moving ring
and another element of the zoom lens barrel with a linear guide mechanism
for guiding the moving ring linearly along the optical axis. If an
excessive load is applied to the moving ring, an engagement of the moving
ring with the another element of the zoom lens barrel through the linear
guide mechanism is disengaged, which may cause the moving ring from coming
off the zoom lens barrel.
A solution to this problem is to increase the strength of the linear guide
mechanism by forming the linear guide mechanism so as to have a
complicated structure. However, if the linear guide mechanism is
complicated, it will be difficult to install the movable ring into the
zoom lens barrel during assembly.
SUMMARY OF THE INVENTION
The present invention provides a retracting mechanism of a zoom lens barrel
including the aforementioned type of zoom lens system, in which the first
lens group and the third lens group are moved together as one body along
an optical axis during a variation of a focal length, wherein the
retracting mechanism can be easily assembled, and wherein each of the
first, second and third lens groups can be linearly guided with
reliability.
According to an aspect of the present invention, a retracting mechanism of
a zoom lens barrel is provided, including a first lens group, a second
lens group and a third lens group, in that order from an object side,
wherein the first lens group and the third lens group are integrally moved
along an optical axis thereof during a zooming operation, and wherein at
least one of the first lens group and the third lens group is moved
relative to the other to reduce a distance therebetween when the zoom lens
barrel is retracted, the retracting mechanism including a first lens group
moving ring which is linearly guided along the optical axis, and supports
the first lens group; a second lens group moving ring which is linearly
guided along the optical axis, and supports the second lens group; a third
lens group moving ring which is linearly guided along the optical axis,
and supports the third lens group, the third lens group moving ring being
allowed to freely approach the first lens group moving ring while being
prevented from moving away from the first lens group moving ring beyond a
moving limit relative to the first lens group moving ring; a cam mechanism
for moving the first lens group moving ring and the second lens group
moving ring in respective moving manners independent of each other along
the optical axis; a biasing device for biasing the third lens group moving
ring in a direction away from the first lens group moving ring; a linear
guide through-slot formed on the second lens group moving ring to be
elongated in a direction parallel to the optical axis; a first linear
guide projection formed on the first lens group moving ring to be engaged
in the linear guide through-slot from outside the second lens group moving
ring, the first linear guide projection including a hanging groove formed
along a substantially center thereof and elongated in a direction parallel
to the optical axis, a rear end of the hanging groove being closed; a
second linear guide projection formed on the third lens group moving ring
to be engaged in the linear guide through-slot from inside the second lens
group moving ring; and a linear moving key projecting from a front end of
the second linear guide projection to be engaged in the hanging groove. A
rear moving limit of the third lens group moving ring relative to the
first lens group moving ring is determined by contact of the linear moving
key with the closed rear end of the hanging groove.
It is desirable for the hanging groove to include a narrow-width groove
portion which communicatively connects with the linear guide through-slot;
and a wide-width groove portion which communicative connects with the
narrow-width groove portion, a width of the wide-width groove portion in a
circumferential direction of the first lens group moving ring being
greater than that of the narrow-width groove portion. It is desirable for
the linear moving key to include a neck portion which is engaged in the
narrow-width groove portion; and a head portion which is engaged in the
wide-width groove portion, a width of the head portion in a
circumferential direction of the first lens group moving ring being
greater than that of the neck portion.
It is desirable for the second lens group moving ring to include a follower
introducing through-slot which extends orthogonal to the linear guide
through-slot to communicatively connect with the linear guide
through-slot; and a first follower introducing groove which extends
parallel to the optical axis to communicative connect with the follower
introducing through-slot, a front end of the first follower introducing
groove communicatively connecting with the follower introducing
through-slot, a rear end of the first follower introducing groove being
open on a rear surface of the second lens group moving ring. The first
lens group moving ring includes a second follower introducing groove which
radially communicatively connects with the follower introducing
through-slot and the hanging groove when the first lens group moving ring
is positioned at a specific position relative to the second lens group
moving ring in the optical axis direction. The linear moving key is
inserted into the hanging groove via the follower introducing
through-slot, the first follower introducing groove and the second
follower introducing groove during assembly of the zoom lens barrel.
It is desirable for the first lens group moving ring, the second lens group
moving ring and the third lens group moving ring to be coaxially arranged
so that the first lens group moving ring is positioned around the second
lens group moving ring, and so that the second lens group moving ring is
positioned around the third lens group moving ring.
It is desirable for the cam mechanism to include a cam ring which is
positioned around the second lens group moving ring to be rotatable
relative to the second lens group moving ring, and includes a plurality of
outer cam grooves formed on an outer peripheral surface of the cam ring,
and a plurality of inner cam grooves formed on an inner peripheral surface
of the cam ring; a plurality of inward cam followers which project
radially inwards from the first lens group moving ring to be engaged in
the plurality of outer cam grooves, respectively; and a plurality of
outward cam followers which project radially outwards from the second lens
group moving ring to be engaged in the plurality of inner cam grooves,
respectively.
It is desirable for the biasing device to be a compression coil spring.
It is desirable for positions of the first lens group moving ring and the
second lens group moving ring in the optical axis direction to be
adjustable by rotating the cam ring to make the second follower
introducing groove and the follower introducing through-slot aligned in
the optical axis direction so that the second follower introducing
grooves, the follower introducing through-slots and the first follower
introducing grooves form an L-shaped follower introducing channel, through
which the linear moving key is inserted into the hanging groove, when the
third lens group moving ring is installed in the zoom lens barrel during
assembly.
The present disclosure relates to subject matter contained in Japanese
Patent Application No. 2003-034959 (filed on Feb. 13, 2003) which is
expressly incorporated herein by reference in its entirety.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be described below in detail with reference to
the accompanying drawings in which:
FIG. 1 is a diagram showing reference moving paths of zoom lens groups of a
zoom lens system provided in an embodiment of a zoom lens barrel according
to the present invention;
FIG. 2 is an exploded perspective view in axial section of the zoom lens
groups and lens support frames therefor;
FIG. 3 is a longitudinal cross sectional view of the embodiment of the zoom
lens barrel according to the present invention, showing an upper half of
the zoom lens barrel from the optical axis thereof in a retracted state;
FIG. 4 is a view similar to that of FIG. 3, and shows an upper half of the
zoom lens barrel from the optical axis thereof at the wide-angle
extremity;
FIG. 5 is a view similar to that of FIG. 3, and shows a lower half of the
zoom lens barrel from the optical axis thereof at the telephoto extremity;
FIG. 6 is a transverse cross sectional view taken along VI--VI line shown
in FIG. 3;
FIG. 7 is a transverse cross sectional view taken along VII--VII line shown
in FIG. 3;
FIG. 8 is an exploded perspective view of a portion of the zoom lens barrel
shown in FIG. 3;
FIG. 9 is an exploded perspective view of a portion of the zoom lens barrel
shown in FIG. 3;
FIG. 10 is an exploded perspective view of a portion of the zoom lens
barrel shown in FIG. 3, showing a first lens group moving ring and
peripheral elements;
FIG. 11 is an exploded perspective view of a portion of the zoom lens
barrel shown in FIG. 3, showing a third lens group moving ring and
peripheral elements;
FIG. 12 is an exploded perspective view of a portion of the zoom lens
barrel shown in FIG. 3, showing a second lens group moving ring and
peripheral elements;
FIG. 13 is a longitudinal view of a portion of the zoom lens barrel shown
in FIG. 3, showing a portion of the second lens group moving ring and
peripheral elements;
FIG. 14 is an exploded perspective view of a portion of the zoom lens
barrel shown in FIG. 3, showing a stationary barrel, a pulse motor
supported by the stationary barrel, and peripheral elements, seen from the
rear side thereof;
FIG. 15 is an exploded perspective view of a portion of the zoom lens
barrel shown in FIG. 3, showing the stationary barrel, a fourth lens group
and peripheral elements;
FIG. 16 is a developed view of a cam/helicoid ring, showing a set of first
cam grooves of the cam/helicoid ring for moving the first lens group and a
set of third cam grooves of the cam/helicoid ring for moving an exterior
ring;
FIG. 17 is a developed view of the first lens group moving ring, the second
lens group moving ring and the third lens group moving ring, showing
linear guide mechanical linkages among the first through third lens group
moving rings;
FIG. 18 is an enlarged view of a portion of the developed view shown in
FIG. 17; and
FIG. 19 is a developed view of the cam/helicoid ring, showing the shapes of
a set of second cam grooves of the cam/helicoid ring for moving the second
lens group.
DESCRIPTION OF THE PREFERRED EMBODIMENT
First of all, a zoom lens system (zoom lens optical system) provided in an
embodiment of a zoom lens barrel of a camera according to the present
invention will be hereinafter discussed with reference to FIGS. 1 through
5. The zoom lens system of the zoom lens barrel 10 is a vari-focal lens
system consisting of four lens groups: a positive first lens group L1, a
negative second lens group L2, a positive third lens group L3 and a
positive fourth lens group L4, in that order from the object side (left
side as viewed in FIG. 3). The first through third lens groups L1, L2 and
L3 are moved relative to one another along an optical axis O to vary the
focal length of the zoom lens system and the fourth lens group L4 is moved
along the optical axis O to make a slight focus adjustment, i.e., to
adjust a slight focus deviation caused by the variation of the focal
length. During the operation of varying the focal length of the zoom lens
system between wide angle and telephoto, the first lens group L1 and the
third lens group L3 move along the optical axis while maintaining the
distance therebetween. The fourth lens group L4 also serves as a focusing
lens group. FIG. 1 shows both moving paths of the first through fourth
lens groups L1 through L4 during the zooming operation and moving paths
for advancing/retracting operation. By definition, a vari-focal lens is
one whose focal point slightly varies when varying the focal length, and a
zoom lens is one whose focal point does not vary substantially when
varying the focal length. However, the vari-focal lens system of the
present invention is also hereinafter referred to as a zoom lens system.
The overall structure of the zoom lens barrel 10 will be hereinafter
discussed with reference to FIGS. 1 through 19. The zoom lens barrel 10 is
provided with a stationary barrel 11 which is fixed to a camera body (not
shown). As shown in FIG. 8, the stationary barrel 11 is provided on an
inner peripheral surface thereof with a female helicoid 11a and a set of
three linear guide grooves 11b which extend parallel to the optical axis
O. The zoom lens barrel 10 is provided inside the stationary barrel 11
with a cam/helicoid ring (cam ring) 12. As shown in FIG. 9, the
cam/helicoid ring 12 is provided, on an outer peripheral surface thereof
in the vicinity of the rear end of the cam/helicoid ring 12, with a male
helicoid 12a which is engaged with the female helicoid 11a of the
stationary barrel 11. The cam/helicoid ring 12 is provided on the thread
of the male helicoid 12a with a spur gear 12b which is always engaged with
a drive pinion 13 (see FIG. 15). The drive pinion 13 is provided in a
recessed portion 11c (see FIG. 3) formed on an inner peripheral surface of
the stationary barrel 11. The drive pinion 13 is supported by the
stationary barrel 11 to be freely rotatable in the recessed portion 11c on
an axis of the drive pinion 13. Accordingly, forward and reverse rotations
of the drive pinion 13 cause the cam/helicoid ring 12 to move forward
rearward along the optical axis O while rotating about the optical axis O
due to the engagement of the drive pinion 13 with the spur gear 12b and
the engagement of the female helicoid 11a with the male helicoid 12a. In
the present embodiment of the zoom lens barrel 10, the cam/helicoid ring
12 is the only element thereof which rotates about the optical axis O.
The zoom lens barrel 10 is provided around the cam/helicoid ring 12 with a
linear guide ring 14. The linear guide ring 14 is provided, on an outer
peripheral surface thereof at the rear end of the linear guide ring 14,
with a set of three linear guide projections 14a which project radially
outwards to be engaged in the set of three linear guide grooves 11b of the
stationary barrel 11, respectively. The linear guide ring 14 is provided,
on an inner peripheral surface thereof at the rear end of the linear guide
ring 14, with a set of three bayonet lugs 14b (only one of them appears in
FIGS. 1 through 4). The cam/helicoid ring 12 is provided, on an outer
peripheral surface thereof immediately in front of the male helicoid 12a
(the spur gear 12b), with a circumferential groove 12c in which the set of
three bayonet lugs 14b are engaged to be rotatable about the optical axis
O in the circumferential groove 12c. Accordingly, the linear guide ring 14
is linearly movable along the optical axis O together with the
cam/helicoid ring 12 without rotating about the optical axis O.
The zoom lens barrel 10 is provided around the cam/helicoid ring 12 with a
first lens group moving ring (first lens frame) 15 which supports the
first lens group L1, and is further provided around the first lens group
moving ring 15 with an exterior ring 16 serving as a light shield member.
The zoom lens barrel 10 is provided inside the cam/helicoid ring 12 with a
second lens group moving ring (second lens frame) 17 which supports the
second lens group L2. As shown in FIGS. 4, 9 and 16, the cam/helicoid ring
12 is provided on an outer peripheral surface thereof with a set of three
first cam grooves C15 for moving the first lens group moving ring 15 and a
set of three third cam grooves C16 for moving the exterior ring 16, and is
further provided on an inner peripheral surface of the cam/helicoid ring
12 with a set of six second cam grooves C17 for moving the second lens
group moving ring 17 (see FIG. 19). The set of three first cam grooves C15
and the set of three third cam grooves C16 are slightly different in
shape, and are apart from one another at predetermined intervals in a
circumferential direction of the cam/helicoid ring 12. The set of six
second cam grooves C17 have the same basic cam diagrams, and includes
three front second cam grooves C17, and three rear second cam grooves C17
which are positioned behind the three front second cam grooves C17 in the
optical axis direction (vertical direction as viewed in FIG. 19),
respectively; the three front second cam grooves C17 are apart from one
another in a circumferential direction of the cam/helicoid ring 12 while
the three rear second cam grooves C17 are apart from one another in a
circumferential direction of the cam/helicoid ring 12. Each of the first
lens group moving ring 15, the exterior ring 16 and the second lens group
moving ring 17 is linearly guided along the optical axis O. A rotation of
the cam/helicoid ring 12 causes the first lens group moving ring 15, the
exterior ring 16 and the second lens group moving ring 17 to move along
the optical axis O in accordance with the contours of the set of three
first cam grooves C15, the set of three third cam grooves C16 and the set
of six second cam grooves C17, respectively.
Linear guide mechanical linkages among the first lens group moving ring 15,
the exterior ring 16 and the second lens group moving ring 17 will be
discussed hereinafter. As shown in FIGS. 4 and 5, the first lens group
moving ring 15 is provided with an outer ring portion 15X, an inner ring
portion 15Y and a flange wall 15Z by which the front end of the outer ring
portion 15X and the front end of the inner ring portion 15Y are connected
to have a substantially U-shaped cross section. The cam/helicoid ring 12
is positioned between the outer ring portion 15X and the inner ring
portion 15Y. Three cam followers 15a which are respectively engaged in the
set of three first cam grooves C15 are fixed to the outer ring portion 15X
in the vicinity of the rear end thereof. The zoom lens barrel 10 is
provided with a first lens group support frame 24 which supports the first
lens group L1. As shown in FIGS. 8 and 9, the first lens group support
frame 24 is fixed to the inner ring portion 15Y at the front end thereof
through a male thread portion and a female thread portion which are formed
on an outer peripheral surface of the first lens group support frame 24
and an inner peripheral surface of the inner ring portion 15Y,
respectively (see FIG. 10). The first lens group support frame 24 can be
rotated relative to the first lens group moving ring 15 to adjust the
position of the first lens group support frame 24 along the optical axis O
relative to the first lens group moving ring 15 to carry out a zooming
adjustment (which is an adjustment operation which is carried out in a
manufacturing process of the zoom lens barrel if necessary).
The linear guide ring 14, which is linearly guided along the optical axis O
by the stationary barrel 11, is provided, on an inner peripheral surface
thereof at approximately equi-angular intervals (intervals of
approximately 120 degrees), with a set of three linear guide grooves 14c
(only one of them appears in FIG. 9), while the outer ring portion 15X of
the first lens group moving ring 15 is provided at the rear end thereof
with a set of three linear guide projections 15b (see FIG. 10) which
project radially outwards to be engaged in the set of three linear guide
grooves 14c, respectively. The outer ring portion 15X is provided with a
set of three assembly slots 15c (see FIGS. 10 and 16), and is further
provided at the rear ends of the set of three assembly slots 15c with a
set of linear guide slots 15d which are communicatively connected with the
set of three assembly slots 15c and are smaller in width than the set of
three assembly slots 15c, respectively. Three linear guide keys 16a which
are fixed to the exterior ring 16 which is positioned between the outer
ring portion 15X and the linear guide ring 14 are engaged in the set of
linear guide slots 15d, respectively. The maximum relative moving distance
between the first lens group moving ring 15 and the exterior ring 16 along
the optical axis O (the difference in shape between the set of three first
cam grooves C15 and the set of three third cam grooves C16) is only a
slight distance, and the length of each linear guide slot 15d in the
optical axis direction is correspondingly short. A set of three cam
followers 16b which are engaged in the set of three third cam grooves C16
are fixed to the set of three linear guide keys 16a, respectively (see
FIGS. 7 and 9).
The zoom lens barrel 10 is provided between the first lens group moving
ring 15 and the exterior ring 16 with a compression coil spring 19 (see
FIGS. 3 through 5). The compression coil spring 19 biases the first lens
group moving ring 15 rearward to remove backlash between the set of three
first cam grooves C15 and the set of three cam followers 15a, and at the
same time, biases the exterior ring 16 forward to remove backlash between
the set of three third cam grooves C16 and the set of three cam followers
16b.
As shown in FIG. 16, the set of three first cam grooves C15 and the set of
three third cam grooves C16 are shaped slightly different from each other
in their respective retracting positions, as compared with their
respective photographing ranges (zooming ranges), so that the exterior
ring 16 advances from the photographing position thereof relative to the
first lens group moving ring 15 to prevent barrier blades of a lens
barrier unit 30 (see FIG. 8) and the first lens group L1 from interfering
with each other when the zoom lens barrel 10 is fully retracted as shown
in FIG. 3. More specifically, as shown in FIG. 16, the shapes of the first
cam grooves C15 and the third cam grooves C16 are determined so that the
distance Q in the optical axis direction between the first cam grooves C15
and the third cam grooves C16 in the preparation ranges (i.e., the range
between the retracted position and the position at which the lens barrier
unit 30 is fully open) is longer than that of the zoom ranges (i.e., the
range between the wide-angle extremity and the telephoto extremity).
Namely, throughout the entirety of the preparation ranges the distance
Q=Q1, however, the distance Q gradually reduces from a position OP2 at a
predetermined distance from a fully opened position OP1 of the lens
barrier unit 30 (i.e., from a position whereby the first lens group L1 and
the lens barrier unit 30 do not interfere with each other), so that the
distance Q=Q2 (<Q1) at the wide-angle extremity, and the distance Q=Q2
in the entirety of the zoom ranges.
It can be seen in FIG. 3 that a clearance c1 between the flange wall 15Z of
the first lens group moving ring 15 and a flange wall 16f of the exterior
ring 16 when the zoom lens barrel 10 is in the retracted position is
greater than that when the zoom lens barrel 10 is in a ready-to-photograph
position as shown in FIG. 4 or 5. In other words, when the zoom lens
barrel 10 is in a ready-to-photograph position as shown in FIG. 4 or 5,
the flange wall 15Z of the first lens group moving ring 15 and the flange
wall 16f of the exterior ring 16 are positioned closely to each other to
reduce the length of the zoom lens barrel 10. The lens barrier unit 30 is
supported by the exterior ring 16 at the front end thereof. The zoom lens
barrel 10 is provided, immediately behind the lens barrier unit 30
(between the lens barrier unit 30 and the flange wall 16f of the exterior
ring 16), with a barrier opening/closing ring 31 (see FIG. 9). Rotating
the barrier opening/closing ring 31 at the retracted position via rotation
of the cam/helicoid ring 12 causes the barrier blades of the lens barrier
unit 30 to open and shut. The mechanism for opening and closing the
barrier blades using a barrier opening/closing ring such as the barrier
opening/closing ring 31 is known in the art. Note that in the illustrated
embodiment, although the shapes of the first cam grooves C15 and the third
cam grooves C16 are determined so that the distance Q (i.e., Q2) is
constant (unchanging) over the entire zoom range, the distance Q (i.e.,
Q2) can be determined so as to change in accordance with the focal length.
Furthermore, the distance Q2 over the zoom range can be determined so as
to be greater than the distance Q1 over the preparation range.
The front end of each third cam groove C16 is open on a front end surface
of the cam/helicoid ring 12 to be formed as an open end C16a (see FIG. 16)
through which the associated cam follower 16b of the exterior ring 16 is
inserted into the third cam groove C16. Likewise, the front end of each
first cam groove C15 is open on a front end surface of the cam/helicoid
ring 12 to be formed as an open end C15a (see FIG. 16) through which the
associated cam follower 15a of the first lens group moving ring 15 is
inserted into the first cam groove C15.
The inner ring portion 15Y of the first lens group moving ring 15 is
provided on an inner peripheral surface thereof with a set of three linear
guide projections 15f which are elongated in a direction parallel to the
optical axis O, while the second lens group moving ring 17 is provided
with a set of three linear guide slots (linear guide through-slots) 17a
which are elongated in a direction parallel to the optical axis O to be
engaged with the set of three linear guide projections 15f to be freely
slidable relative thereto along the optical axis O (see FIGS. 6, 7 and
17). Each linear guide projection 15f is provided along a substantially
center thereof with a hanging groove 15e which is elongated in a direction
parallel to the optical axis O and which has a substantially T-shaped
cross section as shown in FIG. 6. The three linear guide projections 15f
and the three linear guide slots 17a constitute a first linear guide
mechanism. The rear end of each hanging groove 15e is closed (see FIGS. 17
and 18). The second lens group moving ring 17 is provided on an outer
peripheral surface thereof with six cam followers 17c which are engaged in
the set of six second cam grooves C17 of the cam/helicoid ring 12,
respectively.
The zoom lens barrel 10 is provided inside the second lens group moving
ring 17 with a third lens group moving ring (third lens frame) 18 which
supports the third lens group L3. The third lens group moving ring 18 is
provided on an outer peripheral surface thereof with a set of three linear
guide projections 18a which are elongated in a direction parallel to the
optical axis O to be engaged in the set of three linear guide slots 17a of
the second lens group moving ring 17 to be freely slidable relative
thereto along the optical axis O, respectively. The third lens group
moving ring 18 is provided on a center of each linear guide projection 18a
at the front end thereof with a linear moving key (stop projection) 18b
(see FIGS. 11, 17 and 18) which has a substantially T-shaped cross section
to be engaged in the associated hanging groove 15e. The three linear guide
projections 15f, the three hanging groove 15e and the three linear moving
keys 18b constitute a second linear guide mechanism. Furthermore, the
three linear guide slots 17a and the three linear guide projections 18a
constitute a third linear guide mechanism. As shown in FIG. 11, the zoom
lens barrel 10 is provided with a shutter unit 20 which is inserted into
the third lens group moving ring 18 to be positioned in front of the third
lens group L3. The shutter unit 20 is fixed to the third lens group moving
ring 18 by a fixing ring 20a. The zoom lens barrel 10 is provided between
the third lens group moving ring 18 (the fixing ring 20a) and the second
lens group moving ring 17 with a compression coil spring 21 which
continuously biases the third lens group moving ring 18 rearwards relative
to the second lens group moving ring 17. The rear limit of this rearward
movement of the third lens group moving ring 18 relative to the second
lens group moving ring 17 is determined by the three linear moving keys
18b contacting the closed rear ends of the three hanging grooves 15e,
respectively. Namely, when the zoom lens barrel 10 is in a
ready-to-photograph position, each linear moving key 18b remains in
contact with the rear end of the associated hanging groove 15e of the
first lens group moving ring 15 to keep the distance between the first
lens group L1 and the third lens group L3 constant. When the zoom lens
barrel 10 changes from a ready-to-photograph state to the retracted state
shown in FIG. 3, a further rearward movement of the first lens group L1 in
accordance with contours of the set of three first cam grooves C15, after
the third lens group L3 (the third lens group moving ring 18) has reached
the mechanical rear moving limit thereof, causes the first lens group L1
to approach the third lens group L3 while compressing the compression coil
spring 21 (see FIG. 1). Each linear moving key 18b is formed so that the
radially outer end thereof bulges to be prevented from coming off the
associated hanging groove 15e.
Although a biasing force of the compression coil spring 21 can be applied
directly to the second lens group moving ring 17 (i.e., although the
second lens group L2 can be fixed to the second lens group moving ring
17), the second lens group L2 is made to be capable of moving rearward
relative to the second lens group moving ring 17 for the purpose of
further reduction in length of the zoom lens barrel 10 in the retracted
state thereof in the present embodiment of the zoom lens barrel. FIGS. 12
and 13 show this structure for the further reduction in length of the zoom
lens barrel 10. The second lens group moving ring 17 is provided at the
front end thereof with a cylindrical portion 17e having an inner flange
17d. Three linear guide grooves 17f, which extend parallel to the optical
axis direction and open at the front and rear ends thereof, are formed at
equi-angular intervals on the cylindrical portion 17e. The zoom lens
barrel 10 is provided inside the second lens group moving ring 17 with an
intermediate ring (intermediate member) 25. The intermediate ring 25 is
provided at the front end thereof with a flange portion 25a which is
fitted in the cylindrical portion 17e to be freely slidable on the
cylindrical portion 17e in the optical axis direction. An end portion of
the compression coil spring 21 abuts against the flange portion 25a, so
that the flange portion 25a presses against the inner flange 17d due to
the resiliency of the compression coil spring 21. Three guide projections
25d which radially extend outwards are provided on the outer peripheral
surface of the flange portion 25a. The three guide projection 25d are
respectively engaged with the three linear guide grooves 17f of the second
lens group moving ring 17 from the rear side of the second lens group
moving ring 17. Accordingly, the intermediate ring 25 is prevented from
rotating about the optical axis with respect to the second lens group
moving ring 17, and can only relatively move in the optical axis
direction. The front face of the flange portion 25a can move forwards
until sliding contact is made with the rear face of the inner flange 17d.
The zoom lens barrel L2 is provided inside the second lens group moving
ring 17 with a second lens group support frame 26 to which the second lens
group L2 is fixed. A male thread 26b of the second lens group support
frame 26 is screwed into female thread 25e formed on the inner periphery
of the intermediate ring 25. Accordingly, the position of the second lens
group L2 relative to the intermediate ring 25 which is prevented from
rotating about the optical axis can be adjusted in the optical axis
direction (zooming adjustment) by rotating the second lens group support
frame 26 relative to the intermediate ring 25. After this adjustment, the
second lens group support frame 26 can be permanently fixed to the
intermediate ring 25 by putting drops of an adhesive agent into a radial
through hole 25b formed on the intermediate ring 25. The second lens group
support frame 26 is provided on an outer peripheral surface thereof with
an outer flange 26a, and a clearance C2 (see FIG. 13) for the zooming
adjustment exits between a front end surface of the inner flange 17d and
the outer flange 26a. The compression coil spring 21 biases the
intermediate ring 25 forward, and the intermediate ring 25 is held at a
position where the flange portion 25a contacts with the inner flange 17d
when the zoom lens barrel 10 is in a ready-to-photograph state. Namely, on
the one hand, the position of the second lens group L2 is controlled by
the set of six second cam grooves C17 when the zoom lens barrel 10 is in a
ready-to-photograph state; on the other hand, the second lens group
support frame 26 is pushed rearward mechanically by the rear end of the
first lens group support frame 24 to thereby move the outer flange 26a of
the second lens group support frame 26 rearward to a point where the outer
flange 26a contacts with the inner flange 17d when the zoom lens barrel 10
is retracted to the retracted position thereof. This reduces the length of
the zoom lens barrel 10 by a length corresponding to the clearance C2.
The zoom lens barrel 10 is provided immediately behind the intermediate
ring 25 with a light shield ring 27 which is supported by the intermediate
ring 25. As shown in FIG. 12, the light shield ring 27 is provided with a
ring portion 27a and a set of three leg portions 27b which extend forward
from the ring portion 27a at intervals of approximately 120 degrees. Each
leg portion 27b is provided at the front end thereof with a hook portion
27c which is formed by bending the tip of the leg portion 27b radially
outwards. The intermediate ring 25 is provided on an outer peripheral
surface thereof with a set of three engaging holes 25c with which the hook
portions 27c of the set of three leg portions 27b are engaged,
respectively (see FIG. 12). The zoom lens barrel 10 is provided between
the light shield ring 27 and the second lens group support frame 26 with a
compression coil spring 28 having a substantially truncated conical shape
which continuously biases the light shield ring 27 rearwards. When the
zoom lens barrel 10 is retracted toward the retracted position, the light
shield ring 27 approaches the second lens group support frame 26 while
compressing the compression coil spring 28 after reaching the rear moving
limit of the light shield ring 27. The lengths of the set of three
engaging holes 25c in the optical axis direction are determined to allow
the ring portion 27a to come into contact with the second lens group
support frame 26.
The compression coil spring 28 also serves as a device for removing
backlash between the intermediate ring 25 and the second lens group
support frame 26 when the second lens group support frame 26 is rotated
relative to the intermediate ring 25 for the aforementioned zooming
adjustment. The zooming adjustment is performed by rotating the second
lens group support frame 26 relative to the intermediate ring 25 to adjust
the position of the second lens group L2 in the optical axis direction
relative to the intermediate ring 25 while viewing the position of an
object image. This zooming adjustment can be performed with precision with
backlash between the intermediate ring 25 and the second lens group
support frame 26 being removed by the compression coil spring 28.
The zoom lens barrel 10 is provided behind the third lens group moving ring
18 with a fourth lens group support frame 22 to which the fourth lens
group L4 is fixed. As described above, the fourth lens group L4 is moved
to make a slight focus adjustment to the vari-focal lens system to adjust
a slight focal deviation thereof while the first through third lens groups
L1, L2 and L3 are moved relative to one another to vary the focal length
of the zoom lens system, and is also moved as a focusing lens group. The
fourth lens group L4 is moved along the optical axis O by rotation of a
pulse motor 23 (see FIGS. 5 and 14). The pulse motor 23 is provided with a
rotary screw shaft 23a. A nut member 23b is screwed on the rotary screw
shaft 23a to be prevented from rotating relative to the stationary barrel
11. The nut member 23b is continuously biased by an extension coil spring
S in a direction to contact with a leg portion 22a which projects radially
outwards from the fourth lens group support frame 22 (see FIGS. 5 and 15).
The fourth lens group support frame 22 is prevented from rotating by guide
bars 22b, which extend in direction parallel to the optical axis
direction, which are slidably engaged with radial projecting followers 22c
which extend radially outwards from the fourth lens group support frame 22
(see FIGS. 2 and 15). Accordingly, rotations of the pulse motor 23 forward
and reverse cause the fourth lens group support frame 22 (the fourth lens
group L4) to move forward and rearward along the optical axis O,
respectively. Rotations of the pulse motor 23 are controlled in accordance
with information on focal length and/or information on object distance.
Accordingly, in the above described embodiment of the zoom lens barrel,
rotating the cam/helicoid ring 12 by rotation of the drive pinion 13
causes the first lens group moving ring 15, the exterior ring 16 and the
second lens group moving ring 17 to move along the optical axis O in
accordance with contours of the set of three first cam grooves C15, the
set of three third cam grooves C16 and the set of six second cam grooves
C17, respectively. When the first lens group moving ring 15 moves forward
from the retracted position, firstly the three linear moving keys 18b
contact the rear ends of the three hanging grooves 15e, respectively, and
subsequently the third lens group moving ring 18 moves together with the
first lens group moving ring 15 with the three linear moving key 18b
remaining in contact with the rear ends of the three hanging grooves 15e,
respectively. The position of the fourth lens group L4 is controlled by
the pulse motor 23, whose rotations are controlled in accordance with
information on focal length, to make a slight focus adjustment to the
vari-focal lens system to adjust a slight focal deviation thereof. As a
result, reference moving paths as shown in FIG. 1 for performing a zooming
operation are obtained. Rotations of the pulse motor 23 are also
controlled in accordance with information on object distance to perform a
focusing operation.
As described above, the present embodiment of the zoom lens barrel includes
the first lens group L1, the second lens group L2, the third lens group L3
and the fourth lens group L4, in that order from the object side. The
first through third lens groups L1 through L3 are moved along the optical
axis O to vary the focal length of the zoom lens system. During this
variation of focal length, the first lens group L1 and the third lens
group L3 are integrally moved (i.e., with a constant distance
therebewteen) along the optical axis O. In addition, the three cam
followers 15a of the first lens group moving ring 15, which is positioned
around the cam/helicoid ring 12 and supports the first lens group L1, are
respectively engaged in the set of three first cam grooves C15 of the
cam/helicoid ring 12, while the six cam followers 17c of the second lens
group moving ring 17, which is positioned inside the cam/helicoid ring 12
and supports the second lens group L2, are respectively engaged in the set
of six second cam grooves C17 of the cam/helicoid ring 12. The three cam
followers 15a, the three first cam grooves C15, the six cam followers 17c
and the six second cam grooves C17 are elements of the cam mechanism of
the zoom lens barrel 10 to which the present invention is applied.
In addition, the first lens group moving ring 15 is linearly guided along
the optical axis O by the engagement of the set of three linear guide
projections 15b, which project radially outwards from the outer ring
portion 15X of the first lens group moving ring 15, with the set of three
linear guide grooves 14c of the linear guide ring 14, which is linearly
guided along the optical axis O by the stationary barrel 11.
The second lens group moving ring 17 is linearly guided along the optical
axis O by the engagement of the set of three linear guide projections 15f,
which project radially inwards from the inner ring portion 15Y of the
first lens group moving ring 15, with the set of three linear guide slots
17a of the second lens group moving ring 17.
The third lens group moving ring 18 is linearly guided along the optical
axis O by the second lens group moving ring 17; specifically, by the
engagement of the set of three linear guide projections 18a of the third
lens group moving ring 18 with the set of three linear guide slots 17a of
the second lens group moving ring 17. Additionally, the third lens group
moving ring 18 is linearly guided along the optical axis O by the first
lens group moving ring 15 by the engagement of the set of three linear
moving keys (stop projections) 18b, each of which projects radially
outwards from the front end of the associated linear guide projection 18a,
with the set of three hanging grooves 15e, each of which is formed on the
associated linear guide projection 15f. Namely, opposite edges of each
linear guide projection 15f of the inner ring portion 15Y guide the second
lens group moving ring 17 linearly along the optical axis O via the set of
three linear guide slots 17a, while a central portion of each linear guide
projection 15f (i.e., each hanging groove 15e) guides the third lens group
moving ring 18 linearly along the optical axis O. This structure
miniaturizes the linear guide mechanism for guiding the second lens group
moving ring 17 and the third lens group moving ring 18 by effectively
using three peripheral surfaces of each linear guide projection 15f. In
addition, each linear guide slot 17a is formed to be slidably fitted on
opposite side edges of the associated linear guide projection 15f and
opposite side edges of the associated linear guide projections 18a so that
the radial thickness of each linear guide projection 15f and the radial
thickness of the associated linear guide projection 18a are substantially
accommodated within the wall thickness of the second lens group moving
ring 17. This structure makes it possible to increase the strength of the
zoom lens barrel so that each of the second lens group moving ring 17 and
the third lens group moving ring 18 can be reliably guided linearly along
the optical axis O without requiring an increase in diameter of the zoom
lens barrel 10. Moreover, the zoom lens barrel 10 has been miniaturized to
be smaller than a conventional similar zoom lens barrel due to the above
described structure wherein the outer ring portion 15X of the first lens
group moving ring 15 is linearly guided along the optical axis O by the
linear guide ring 14 while each of the second lens group moving ring 17
and the third lens group moving ring 18 is linearly guided along the
optical axis O by the inner ring portion 15Y of the first lens group
moving ring 15. Accordingly, since the third lens group moving ring 18 is
linearly guided along the optical axis O by two members: the first lens
group moving ring 15 and the second lens group moving ring 17, the third
le
