U.S. patent application number 09/771936 was filed with the patent office on 2001-09-06 for zoom lens barrel and camera.
Invention is credited to Inoue, Norihiro, Shintani, Dai, Uno, Tetsuya.
Application Number | 20010019456 09/771936 |
Document ID | / |
Family ID | 18548237 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010019456 |
Kind Code |
A1 |
Uno, Tetsuya ; et
al. |
September 6, 2001 |
Zoom lens barrel and camera
Abstract
A zoom lens barrel which is an integrated zoom and focus drive
type zoom lens barrel that moves lens units on a single zoom line
having plurality of focusing sections and plurality of zooming
sections, wherein the single zoom line has characteristic that the
"rate of change of the relative distance of the two lens units with
regard to a barrel rotation angle" in each focusing section becomes
smaller in the focusing sections of the telephoto side.
Inventors: |
Uno, Tetsuya; (Osaka,
JP) ; Shintani, Dai; (Osaka, JP) ; Inoue,
Norihiro; (Kashiba-shi, JP) |
Correspondence
Address: |
MCDERMOTT, WILL & EMERY
600 13th Street, N.W.
Washington
DC
20005-3096
US
|
Family ID: |
18548237 |
Appl. No.: |
09/771936 |
Filed: |
January 30, 2001 |
Current U.S.
Class: |
359/694 ;
359/745; 359/822; 359/823 |
Current CPC
Class: |
G02B 7/10 20130101; G02B
15/142 20190801 |
Class at
Publication: |
359/694 ;
359/745; 359/822; 359/823 |
International
Class: |
G02B 015/14; G02B
013/02; G02B 007/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 2000 |
JP |
2000-021882 |
Claims
What is claimed is:
1. A camera comprising: a first lens unit; a second lens unit; a
cam mechanism which moves the first lens unit and the second lens
unit on a single zoom line consisted of plurality of focusing
sections and plurality of zooming sections; wherein a rate of
change of the relative distance of the first lens unit and the
second lens unit with regard to a barrel rotation angle in each
focusing section becomes smaller in the focusing sections of the
telephoto side.
2. A camera according to claim 1, wherein said each focusing
section has a constant movement amount of the focus position with
regard to the barrel rotation angle.
3. A camera according to claim 1, wherein said each focusing
section has a constant value which is the amount of movement of the
focus position relative to the barrel rotation angle divided by the
zoom lens F value
4. A lens barrel comprising: a first lens unit; a second lens unit;
a cam mechanism which moves the first lens unit and the second lens
unit on a single zoom line consisted of plurality of focusing
sections and plurality of zooming sections; wherein a rate of
change of the relative distance of the first lens unit and the
second lens unit with regard to a barrel rotation angle in each
focusing section becomes smaller in the focusing sections of the
telephoto side.
5. A lens barrel according to claim 4, wherein said each focusing
section has a constant movement amount of the focus position with
regard to the barrel rotation angle.
6. A lens barrel according to claim 4, wherein said each focusing
section has a constant value which is the amount of movement of the
focus position relative to the barrel rotation angle divided by the
zoom lens F value
7. A lens drive method which moves a plural lens unit on a single
zoom line consisted of plurality of focusing sections and plurality
of zooming sections, the method comprising: moving the lens units
at a first rate of change of the relative distance of the lens
units with regard to a barrel rotation angle in a first focusing
section; moving the lens units at a second rate of change of the
relative distance of the lens units with regard to the barrel
rotation angle in a second focusing section which positioned in the
telephoto side than the first focusing section, wherein the second
rate is smaller the first rate.
Description
[0001] This application is based on Patent Application No.
2000-21882 filed in Japan, the content of which is hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a lens barrel which
accomplishes zooming and focusing by a single drive mechanism, and
a camera provided with the lens barrel.
[0004] 2. Description of the Related Art
[0005] Integrated zoom and focus drive mechanisms are known which
move various lens units on a single zoom line including alternating
zooming intervals and focusing intervals as a construction for
reducing cost and achieving compactness of the zoom lens barrel. An
example of such a construction is described below with reference to
FIGS. 1A and 1B.
[0006] FIGS. 1A and 1B are examples of zoom charts of a two-section
zoom lens barrel which accomplishes focusing by a single lens unit
(first section). This zoom lens barrel includes "a stationary
barrel which does not move relative to the camera body", "a cam
barrel which advances and retracts relative to the stationary
barrel" and "first and second lens units which advance and retract
relative to the cam barrel" identically to an embodiment of the
present invention which is described later.
[0007] In FIG. 1A, straight line 1 presents the extension lead of
the cam barrel relative to the stationary barrel, straight line 3
represents the relative extension lead of the first lens unit
(first section) with regard to the cam barrel, and step line 2
represents the relative extension lead of the second lens unit
(second section) with regard to the cam barrel. Accordingly, the
amount of extension of the first lens unit relative to the
stationary barrel is the combination of the straight lines 1 and 3,
and is represented by the straight line 13 in FIG. 1B. Similarly,
the amount of extension of the second lens unit relative to the
stationary barrel is the combination of the straight line 1 and the
step line 2, and is represented by the step line 12 in FIG. 1B.
[0008] This zoom lens barrel utilizes four middle steps M1, M2, M3
and M4 between telephoto end (tele) and wide angle end (wide),
i.e., accomplishes zooming in a total of six steps, so as to
accomplish focusing (focusing section F) using the part
corresponding to the flat portions of the step line 12, and
accomplish zooming (zooming section) using the other parts. In this
way in an integrated zoom and focus drive mechanism, each lens unit
moves on a single zoom line including alternating plurality of zoom
sections and plurality of focus sections.
[0009] The curve 2' in FIG. 1A represents the extension lead of the
second lens unit (second section) relative to the cam barrel in the
case of continuous zooming. Accordingly, the amount of extension of
the second lens unit relative to the stationary barrel is
represented by the curve 12' in FIG. 1B. During continuous zooming,
focusing at each zoom position is accomplished by changing the
relative distance of both lens units using another drive
mechanism.
[0010] As shown in FIG. 1B, the first section normally moves
linearly along the zoom line 13 across all zoom regions, and the
second section does not move in the optical axis direction in the
horizontal parts (focusing section F) of the step-like zoom line
12. That is, the "rate of change of the relative distance between
the first lens unit and the second lens unit" with regard to a
rotation amount (rotation angle) is the same in all focusing
sections.
[0011] In general, it can be said that, in the zoom lens barrel,
there is a large amount of movement of the focus position from the
wide side to the tele side even when the change in the relative
distance between the first section and the second section is the
same. Accordingly, in a conventional integrated drive type zoom and
focus zoom lens barrel wherein the rate of change of the relative
distance between the first section and second section with regard
to a barrel rotation angle (a constant rotation amount) is
identical for all focusing sections, the amount of movement of the
focus position increases relative to the same barrel rotation angle
toward the tele side, as shown in FIGS. 1A and 1B, such that the
focus precision disadvantageously decreases toward the tele
side.
[0012] To eliminate this problem, consideration has been given to
increasing the focusing resolution on the tele side as the total
amount of rotation of the lens barrel increases, or increasing the
amount of barrel rotation in the focusing section as the length of
the zooming section becomes shorter. However, when the total amount
of rotation of the barrel is increased, the total length of the cam
channel (e.g., cam channel 210 shown in FIGS. 2-4) formed on the
cam barrel also increases, and the strength of the barrel is
reduced in that part, and the analogous cam channel overlap.
Furthermore, when the number of zooming sections is reduced, the
pressure angle increases in each zooming section, and as a result
the smooth rotation of the barrel is hindered so as to produce
another problem in that a large drive force is required for barrel
rotation.
SUMMARY OF THE INVENTION
[0013] An object of the present invention is to provide a zoom
mechanism using an integrated zoom and focus drive method which
does not increase the total rotation of the barrel, does not
increase the pressure angle in the zooming section, and does not
adversely affect focus precision on the tele side.
[0014] The present invention attains these objects by providing a
zoom camera having the characteristics describe below.
[0015] The zoom camera of the present invention has an integrated
zoom and focus drive type zoom lens barrel which moves on a single
zoom line and includes alternating plurality of focusing sections
and plurality of zooming sections. With regard to the "adjoining
two lens units whose relative distance unit change most greatly
affects the amount of movement of the focus position", the "rate of
change of the relative distance of the two lens units with regard
to a barrel rotation angle" in each focusing section becomes
smaller in the focusing sections of the tele side.
[0016] In general, "the amount of movement of the focus position
with regard to the change in the relative unit distance of the two
opposing lens units" increases from the wide side to the tele side.
On the other hand, "the amount of movement of the focus position
relative to a barrel rotation angle" is expressed as the sum of
"the amount of movement of the focus position (with regard to the
change in the relative unit distance of the two opposing lens
units" and "the rate of change of the relative distance of the two
lens units with regard to the barrel rotation angle." Accordingly,
"the amount of movement of the focus position relative to the
barrel rotation angle" can be fixed in the entire zoom range by
setting the rate of change of the relative distance of the two lens
units with regard to the barrel rotation angle" to be smaller in
conjunction with the advance to the tele side. That is, the focus
precision is not adversely affected with the advance to the tele
side.
[0017] When there are only two lens units, the "rate of change of
the relative distance of the two lens units with regard to the
barrel rotation angle" may be reduced in conjunction with the
advance to the tele side in observation of these two lens units.
When there are three or more lens units, similar setting is
accomplished in observation of "the amount of unit change of the
relative distance of the two opposing lens units to affect the
greatest influence on the movement of the focus position". Among
the two opposing lens units, the two opposing lens units affecting
the greatest influence on the movement of the focus position
differs depending on the specific lens construction, but the
present invention includes all such lens units.
[0018] According to the present invention, the two opposing lens
units wherein the amount of unit change in their relative distance
most greatly influences the movement of the focus position in the
aforesaid zoom lens camera are constructed such that the rate of
change of the relative distance of the two lens units with regard
to a barrel rotation angle in each focusing section becomes smaller
advancing to the tele side, and thereby provides a method whereby
the amount of movement of the focus position is near constant
relative to the throughout the entire zoom region.
[0019] The zoom camera of the present invention is constructed such
that "the amount of movement of the focus position is near constant
relative to the barrel rotation angle throughout the entire zoom
region" and each lens unit moves on the zoom line. In this case the
consideration is not given to the rate of change of the relative
distance of only the two specific lens units among a plurality of
lens units, but rather consideration is given to the change in
relative distance between several groups of opposed lens units
(desirably all groups).
[0020] In the present invention, "the amount of movement of the
focus position relative to a barrel rotation angle is the amount
obtained by dividing by the zoom lens F value", but each lens unit
moves on the zoom line such that the amount of such change remains
constant throughout the entire zoom region. Since the focus width
determined from the diameter of the allowable circle of confusion
permitted at each focal length is proportional to the F value,
consideration of the change not only in the amount of movement of
the focus position but also in F value is advantageous from the
perspectives of rotation angle and cam optimization. In this case
also consideration is given to the change in relative distance
between several groups (and desirably all groups) of lens
units.
[0021] These and other objects, advantages and features of the
invention will become apparent from the following description
thereof taken in conjunction with the accompanying drawings which
illustrate specific embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] In the following description, like parts are designated by
like reference numbers throughout the several drawings.
[0023] FIGS. 1A and 1B are zoom line charts of a conventional
integrated zoom and focus drive type camera showing the focusing by
a first lens unit and zooming by a second lens unit;
[0024] FIG. 2 is a cross section view of the zoom lens barrel in
the camera of the present invention at the collapsed position;
[0025] FIG. 3 is a cross section view of the zoom lens barrel of
FIG. 2 at the wide position;
[0026] FIG. 4 is a cross section view of the zoom lens barrel of
FIG. 2 at the tele position;
[0027] FIG. 5 is a development view showing the exterior surface
shape of the cam barrel included in the zoom lens barrel of FIG.
2;
[0028] FIG. 6 is a zoom line chart of the camera of a first
embodiment of the invention;
[0029] FIG. 7 is a zoom line chart of the camera of a second
embodiment of the invention;
[0030] FIG. 8 is a zoom line chart of a modification of the zoom
line chart of FIG. 7;
[0031] FIG. 9 is a zoom line chart of the camera of a third
embodiment of the invention; and
[0032] FIG. 10 is a zoom line chart of the camera of a fourth
embodiment of the invention;
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] A first embodiment of the present invention is described in
detail hereinafter with reference to the accompanying drawings.
[0034] FIG. 2 is a cross section view of a lens barrel at the
collapsed position. In the drawing, reference number 90 refers to
an external shell forming the front surface of the camera body. A
stationary barrel 100 is fixedly attached to the camera body so as
to be unmovable, and a cam barrel 200 is housed in the interior
side of the stationary barrel 100. The cam barrel 200 has a
helicoid gear 201 on its exterior surface on the end on the
photographer side, as shown in the development view of FIG. 5. The
helicoid gear 201 comprises "a band gear 201a formed across the
entire surface of the cam barrel 100" and "a female helicoid 201b
formed at a traverse inclination to the gear 201a". The cam barrel
200 is rotated within the stationary barrel 100 by a drive force
from a drive gear 150 received by the gear 201a.
[0035] The female helicoid 201b engages a male helicoid 101 formed
on the interior surface of the stationary barrel 100. Accordingly,
when the cam barrel 200 is rotated within the stationary barrel
100, the cam barrel 200 extends out toward the anterior direction
relative to the stationary barrel 100 (i.e., relative to the camera
body). The cam barrel 200 passes through the wide angle end (wide)
shown in FIG. 3, and reaches the telephoto end (tele) shown in FIG.
4. In this way the cam barrel 200 advances across the stationary
barrel 100 in the optical axis direction, and the total length of
the drive gear 150 is approximately equal to the length of the
stationary barrel 100 such that a drive force can be transmitted
even when the cam barrel 200 is at any position relative to the
stationary barrel 100. Since the male helicoid 101 is formed at a
fixed (constant) lead angle across the entire zoom area, the amount
of extension of the cam barrel 200 is linear relative to the
rotation angle.
[0036] As shown in FIGS. 2-4, a combined rectilinear guide barrel
400 and advance barrel 300 are accommodated within the cam barrel
200. Although the rectilinear guide barrel 400 is relatively
rotatable with regard to the cam barrel 200, it is also connected
by a bayonet connector 401 so as to be relatively unmovable in the
optical axis direction. The rectilinear guide barrel 400 is
provided with a part 402a of a flange 402 provided on the end on
the photographer side which extends to the exterior side in the
radius direction, and this part 402a engages a rectilinear guide
channel 102 provided on the interior surface of the stationary
barrel 100. For this reason the rectilinear guide barrel 400 is
relatively unrotatable with regard to the stationary barrel 100,
and is relatively movable in the optical axis direction.
[0037] Accordingly, when the cam barrel 200 rotates within the
stationary barrel 100, the rectilinear guide barrel 400 advances in
the optical axis direction together with the cam barrel 200, and at
this time the rectilinear guide barrel 400 rotates relative to the
cam barrel 200, but does not rotate relative to the stationary
barrel 100. The rectilinear guide channel 102 and the flange
projection 402a only appear once in each of the FIGS. 2-4, they are
actually provided in plurality in the circumferential
direction.
[0038] The advance barrel 300 is relatively advancable in the
optical axis direction with regard to the rectilinear guide barrel
400, but relative rotation is not possible. That is, since the
rectilinear guide barrel 400 is relatively unrotatable with regard
to the stationary barrel 100, as a result the advance barrel 300
also is relatively unrotatable with regard to the stationary barrel
100. However, a specific helicoid 350 is formed on the exterior
surface of the advance barrel 300, and this helicoid 350 engages a
specific helicoid 230 formed on the interior surface of the cam
barrel 200. Accordingly, when the cam barrel 200 is rotated within
the stationary barrel 100, the advance barrel 300 is guided by the
rectilinear guide barrel 400 via the interaction between these
helicoids 350 and 230, and advances in specific movement in the
optical axis direction relative to the cam barrel 200. The amount
of relative movement of the advance barrel 300 with regard to the
stationary barrel 100 is expressed as the sum of "amount of
movement in the optical axis direction of the cam barrel 200
relative to the stationary barrel 100" and "the amount of movement
in the optical axis direction of the advance barrel 300 relative to
the cam barrel 200". As shown in FIGS. 2-4, since the advance
barrel 300 integratedly holds a first lens unit 500 through a
support frame 501 (focus lens unit support frame), the movement of
the advance barrel 300 is the movement of the first lens unit
500.
[0039] The movement of a second lens unit 600 (second section) is
described below. A cam follower pin 602 protruding radially from
lens frame 601 holding the second lens unit 600 engages the
interior of a cam channel 210 having a specific shape formed on the
interior surface of the cam barrel 200. Although only a single cam
follower pin 602 is represented in each cross section of FIGS. 2-4,
actually three cam follower pins protrude from the surface of the
ring-shaped lens frame 601. On the other hand, three rectilinear
guide slots 301 corresponding to the cam follower pins extend
linearly in the optical axis direction on the wall of the advance
barrel 300. As with the cam follower pins 602, only a single
rectilinear guide slot 301 is shown in the cross section views of
FIGS. 2-4.
[0040] As described previously, the advance barrel 300 does not
rotate relative to the stationary barrel 100 even when the cam
barrel 200 rotates relative to the stationary barrel 100. In other
words, the cam barrel 200 and the advance barrel 300 rotate
relatively. Accordingly, the follower pin 602 engaged with both the
linear guide slot 301 formed on the advance barrel 300 and the cam
channel 210 formed on the interior surface of the cam barrel 200
moves in the optical axis direction relative to the cam barrel 200
guided by the advance guide slot 301 when the cam barrel 200 is
rotated. Since the cam barrel 200 itself also moves relative to the
stationary barrel 100, the result is that the amount of relative
movement of the second lens unit 600 held by the lens frame 601
provided with a follower pin 602 with regard to the stationary
barrel 100 is expressed as the sum of "the amount of movement in
the optical axis direction of the cam barrel 200 relative to the
stationary barrel 100" and "the amount of movement in the optical
axis direction of the lens frame 601 relative to the cam barrel
200".
[0041] As can be understood from the description above, the amount
of movement of the first lens unit 500 relative to the stationary
barrel 100 can be determined by "the shape of each helicoid 230 and
350 determining the amount of relative movement of the cam barrel
200 and the advance barrel 300". Furthermore, the amount of
movement of the second lens unit 600 relative to the stationary
barrel 100 can be determined by "the shape of the cam channel 210
determining the amount of relative movement of the cam barrel 200
and the lens frame 601". In other words, A zoom lens barrel having
various zoom lines can be constructed by suitably changing the
shape of each of the aforesaid helicoids and cam channel. The
present invention suitably selects these shapes to set the amount
of relative movement of each lens unit (shape of zoom line chart)
as described below, and in this way sets the amount of movement of
the focus position relative to a barrel rotation angle so as to be
equal in all zoom sections, and so as to be proportional to the F
value of the zoom lens. Conversely, in the present invention, the
shape of the zoom line chart itself is important as described
below, and, therefore, and although specific examples of shapes of
helicoids and cam channels are used, the present invention is not
limited to these examples. Each zoom line described below is
dependent on the helicoids and cam channel formed on the plurality
of parts comprising the barrel, and the total amount of movement of
each lens unit is expressed relative to the camera body.
[0042] FIG. 6 shows the zoom line chart of a first embodiment of
the invention. In the example of FIG. 6, the zoom lens barrel has a
first and second lens units, wherein the first lens unit moves
along zoom line 21, and the second lens unit moves along the zoom
line 22. In this zoom lens barrel, the zoom line 22 becomes
horizontal in focusing sections F at WIDE, M1, M2, M3 and TELE.
That is, during focusing, the second lens unit does not move in the
optical axis direction, and only the first lens unit performs
focusing between infinity .infin. and shortest S.
[0043] A characteristic of the zoom line chart of FIG. 6 is that
the slope of the zoom line 21 in each focusing section becomes
smaller in advancing through the focusing sections to the tele
side. That is, since the zoom line 22 is horizontal in each
focusing section, when "the rate of change of the relative distance
of both lens units with regard to a barrel rotation angle" is
designated A (A1, A2, A3, A4, A5), the value of A becomes smaller
advancing through the focusing sections toward the tele side
(A1<A2<A3<A4<A5).
[0044] On the other hand, generally when "the amount of movement of
the focus position relative to the change in the relative unit
distance of both lens units" is designated B (B1, B2, B3, B4, B5),
the value of B increases toward the tele side
(B1>B2>B3>B4>B5). Since "the amount of movement of the
focus position relative to a barrel rotation angle" can be
expressed as A.times.B, the value of A.times.B can be fixed in all
zoom regions by setting the value of A so as to become smaller in
conjunction with the advance to the tele side. When strictly
considering "the amount of movement of the focus position relative
to a barrel rotation angle" not only is it desirable to consider
the change in the value of B, but it is also desirable to change in
the Fno (F value) of the zoom lens. In this case when designating
B'=B/Fno, the value of B' often becomes greater with the advance to
the tele side. Accordingly, the value of A.times.B' can be set so
as to be equal in all zoom regions by setting the value of A to
become smaller in conjunction with the advance toward the tele
side. In contrast, in the conventional zoom lens barrel shown in
FIGS. 1A and 1B wherein the value of A is fixed in all zoom
regions, the value of A.times.B (or A.times.B') becomes greater in
conjunction with the advance to the tele side.
[0045] FIG. 7 shows the zoom line chart of a second embodiment of
the invention. In the example shown in FIG. 7, there are two lens
units similar to the example shown in FIG. 6, however, this example
differs from that of FIG. 6 in that both the first lens unit and
the second lens unit move in the optical axis direction during
focusing. The first lens unit moves along the zoom line 31, and the
second lens unit moves along the zoom line 32.
[0046] Since only the first lens unit moves in the optical axis
direction in the focusing sections in the example of FIG. 6, only
"the change in the relative distance of both lens units" influences
the amount of movement on the focus position. In contrast, since
both lens units move in the focusing sections in the example of
FIG. 7, not only does "the change in the relative distance of the
two lens units" but also "the change in distance between the second
lens unit and the film surface" affects the amount of movement of
the focus position. Accordingly, ideally the zoom lines of both
lens units are determined considering both such influences.
However, since the influence produced by "the change in distance
between the second lens unit and the film surface" is small
compared to the influence produced by "the change in the relative
distance of the two lens units" only "the change in the relative
distance of the two lens units" is focused on in the example of
FIG. 7.
[0047] In the example of FIG. 7, since the first lens unit normally
moves linearly across all zoom regions, the zoom line 31 has a
fixed slope. On the other hand, the slope of the zoom line 32 is
zero (horizontal) in the focusing section at the widest angle side.
For this reason the slope of the zoom line 32 in each focusing
section is designed so as to increase with the advance through
focusing sections on the tele side such that the slope of the zoom
line 32 in each focusing section approaches the slope of the zoom
line 31. In this way the difference in the slopes of the zoom lines
31 and 32 becomes smaller with the advance through focusing
sections on the tele side, and the value of the aforesaid rate of
change A consequently becomes smaller. On the other hand, the
contrasting modification shown in FIG. 8 illustrates the case
wherein as the barrel extends, the photographic distance shortest S
to infinity .infin. on each focusing section conversely to the
example of FIG. 7. In this case since the slope of the zoom line
32' is set greater than the slope of the zoom line 31' in the
focusing section on the wide side, such that the rate of change A
becomes smaller with the advance through the focusing sections to
the tele side, and the slope of the zoom line 32' in each focusing
section is designed to become smaller with the advance through the
focusing sections on the tele side
(C1<C2<C3<C4<C5).
[0048] FIG. 9 shows a zoom line chart of a third embodiment of the
invention. In the example of FIG. 9, the zoom lens barrel is
provided with three lens units, i.e., first, second, and third lens
units, wherein the first lens unit moves along the zoom line 41,
the second lens unit moves along the zoom line 42, and the third
lens unit moves along the zoom line 43. In this zoom lens barrel
the zoom line 41 and 43 are horizontal in the focusing sections.
That is, during focusing the first and third lens units do not move
in the optical axis direction, and focusing is accomplished by only
the second lens unit.
[0049] In the case of three lens units, since there are two groups
of opposing lens pairs, ideally the zoom line chart of each lens
unit is set considering the amount of change in F value and the
amount of movement of the focus position relative to the change in
the relative distance of two groups of lens units (this is the same
for four or more lens units). However, for simplicity in the
example of FIG. 9, we focus on "two opposing lens units, and the
maximum influence of the amount of unit change in their relative
distance on the movement of the focus position" and we use an idea
similar to the cases of only two lens units as shown in FIGS. 6-8.
That is, with regard to the two opposing lens units, "the rate of
change A of the relative distance of both lens units with regard to
a barrel rotation angle" becomes smaller with the advance through
the focusing sections on the tele side. Whether "the amount of
change in the relative unit distance of the first lens unit and the
second lens unit" or "the amount of change in the relative unit
distance of the second lens unit and the third lens unit" exerts
the greatest influence on the amount of movement of the focus
position differs depending on the specific construction of each
lens unit. FIG. 9 shows an example wherein the greatest influence
is exerted by the second lens unit and the third lens unit. A
similar idea is appropriate when four or more lens units are used.
The case of only two lens units is thought to be equivalent to the
case of "two opposing lens units, wherein the amount of change in
the relative unit distance between the lens units exerts the
greatest influence on the amount of movement of the focus
position".
[0050] When focusing on the second lens unit and the third lens
unit, the slope of the zoom line 42 in each focusing section must
become smaller with the advance through the focusing sections on
the tele side, similar to the example of FIG. 6. Actually, it is
understood that the zoom line 42 of FIG. 9 has this construction
(D1<D2<D3<D4<D5). In this way the value of A.times.B
(or A.times.B') can be fixed in all zoom regions similar to the
example of FIG. 6.
[0051] FIG. 10 shows the zoom line chart of a fourth embodiment of
the invention. In the example of FIG. 10 there are three lens units
similar to the example of FIG. 9, but this example differs from
that of FIG. 9 in that all the first through third lens units move
in the optical axis direction during focusing. The first lens unit
moves along the zoom line 51, the second lens unit moves along the
zoom line 52, and the third lens unit moves along the zoom line
53.
[0052] In the example of FIG. 9, since only two lens units move in
the optical axis direction in the focusing sections, only "the
change in the relative distance of each lens unit" influences the
amount of movement of the focus position. In contrast, since the
third lens unit also moves in the focusing section in the example
of FIG. 10, "the change in the distance between the third lens unit
and the film surface" also influences the amount of movement of the
focus position. Accordingly, ideally all such influences are
considered when determining the zoom line chart of each lens unit.
However, in this case "the change in distance between the third
lens unit and the film surface" is ignored for the same reason we
ignored "the change in distance between the second lens unit and
the film surface" in the examples of FIGS. 7 and 8. Furthermore,
the change in the relative distance of the second lens unit and the
third lens unit is considered as having a greater effect on the
movement of the focus position similar to the example of FIG.
9.
[0053] In the example of FIG. 10, the third lens unit normally
moves linearly in all zoom regions. Accordingly, the slope of the
zoom line 52 in each focusing section is designed so as to increase
with the advance through focusing sections on the tele side such
that the slope of the zoom line 52 in each focusing section
approaches the slope of the zoom line 53
(E1>E2>E3>E4>E5). For this reason the difference in the
slopes of the zoom lines 52 and 53 becomes smaller with the advance
through focusing sections on the tele side, and the value of the
aforesaid rate of change A consequently becomes smaller.
[0054] Although preferred embodiments of the invention have been
described in the foregoing detailed description and illustrated in
the accompanying drawings, it will be understood that the invention
is not limited to the embodiments disclosed, but is capable of
numerous rearrangements, modifications and substitutions of parts
and elements without departing from the spirit of the invention.
Accordingly, the present invention is intended to encompass such
rearrangements, modification and substitutions of parts and
elements as fall within the spirit and scope of the invention.
* * * * *