Interchangeable objective lens single-lens reflex camera focusing device

A single lens reflex camera includes a vertical open topped U-shaped bracket mounted in the camera body below the pentaprism, a forwardly located lens mount separably coupled to an objective lens and pairs of links mutually pivoted between their ends connected between the bracket arms and corresponding edges of the lens mount to support the latter in a fixed orientation for linear longitudinal movement along the camera optical axis. A light tight collapsible conduit extends between the camera body and lens mounts and includes telescoping members with relatively slidable side and bottom walls and an accordian top wall. A rack carrying slide arm projects rearwardly from the lens mount and is engaged by a motor driven gear to longitudinally shift the lens mount. The motor is controlled manually or in response to a focus detecting device and the lens mount may be motor advanced and retracted or motor advanced and spring retracted. The lens diaphragm is automatically stopped down by a camera housed mechanism and diaphragm control information is transmitted from the lens mount to the camera body.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to improvements in cameras and it 
relates particularly to an improved motor focussed, single-lens reflex 
camera of the interchangeable objective lens type. 
In the conventional objective lens exchangeable single-lens reflex cameras, 
focussing of the objective lens is performed by rotating a focussing ring 
provided on the objective lens barrel. However, when an automatic 
focussing device is incorporated in the single-lens reflex camera and a 
drive device such as an electric motor controlled by the automatic 
focussing device is used to rotate the focussing ring for focussing an 
objective lens, it is almost impossible to control the focus of all types 
of objective lenses, since the distance between the focussing and the 
camera body varies with the type of objective lens, as does the force 
required for rotating the focussing ring. Even if, in such type of camera, 
it is possible to automatically control the focus of all types of 
objective lenses a complex interlocking mechanism must be provided, 
thereby posing the problem of an appreciable increase in the size and 
price of the camera. In an attempt to solve this problem, there has been 
proposed a device in which an entire objective lens is longitudinally 
moved along the camera optical axis for controlling focus (U.S. Pat. No. 
3,798,660 granted Mar. 19, 1979). With such device, however, the lens 
mounting member of the camera to which the exchangeable objective lens is 
mounted, is supported by a ring rotated by a motor within the camera and 
the rotatable ring itself serves as a guide member therefor, or the lens 
mounting member is restricted to movement along the optical axis by a 
guide pin fixed to the camera body. As a result, the length of the 
available lens shift is greatly limited, posing a further problem. 
Increasing the length of the available lens shift in such a device 
requires that the length of a rotatable ring supporting the lens mounting 
member be increased along the optical axis or that the guide pin be 
lengthened. However, such increase in size results in a larger camera 
body, causing much inconvenience. Consequently, the devices heretofore 
proposed possess the drawback that the length of available lens shift 
cannot be increased without an increase in the camera size. 
Furthermore, with the earlier structures, a lens mounting member on which 
an exchangeable objective lens is mounted is formed as a cylindrical 
member, part of which is positioned near the viewer penta prism. In 
addition, the lens mounting member and its support must be thick and 
sturdy enough to withstand the weight of an exchangeable objective lens 
which is coupled to the lens mounting member, thereby necessitating the 
provision of a large space near the penta prism. Therefore, the earlier 
structures have the lens mounting member and the supporting member 
therefore assembled near the camera viewer penta prism, the design freedom 
of which is greatly impeded in terms of the penta prism arrangement. 
SUMMARY OF THE INVENTION 
It is a principal object of the present invention to provide improved 
single lens reflex camera focussing mechanism. 
Another object of the present invention is to provide an improved focussing 
mechanism in an interchangeable objective lens single-lens reflex camera 
with which focussing is effected by moving the entire objective lens along 
its optical axis. 
Still another object of the present invention is to provide an improved 
focussing mechanism in which an increase in the length of the available 
lens shift along the optical axis is achieved without any increase in the 
size of the camera body. 
A further object of the present invention is to provide a focussing 
mechanism which includes almost none of its component parts near the 
camera pentaprism thereby permitting freedom of design without interfering 
with the pentaprism arrangement. 
Still a further object of the present invention is to provide a mechanism 
of the above nature characterized by its reliability, ruggedness, ease and 
efficiency of operation, minimum space consumption, low cost and great 
versatility and adaptability. 
The above and other objects of the present invention will become apparent 
from a reading of the following description taken in conjunction with the 
accompanying drawings which illustrate a preferred embodiment thereof. 
A single lens reflux camera in accordance with the present invention 
comprises a body member having a front aperture and a pentaprism, an 
apertured mounting member having coupling means for separably engaging an 
interchangeable objective lens, a pair of laterally spaced longitudinally 
extendable retractable support members extending between the body member 
and mounting member and supporting the mounting member for longitudinal 
movement only at a fixed orientation, an extendable collapsible light 
tight conduit extending between the mounting and body members in 
registering with the apertures therein and control motor means in said 
body member for longitudinally advancing and retracting the mounting 
member. 
In accordance with a preferred form of the improved camera a laterally 
extending U-shaped bracket is affixed to the body member and includes a 
bottom cross arm and side arms in opposite sides of the body member front 
aperture and is open at its top and the mounting member comprises a plate 
with a bottom and vertical side flanges. Each of the support members 
comprises a pair of levers or links mutually pivoted intermediate their 
ends and each lever being pivotally connected at its ends to the bracket 
side and bottom arms and to a mounting plate flange respectively, one end 
of each lever being vertically slidably coupled to the bracket side arm or 
mounting plate flange. The control motor means includes a motor controlled 
in response to a manual switch or a focus detecting network and coupled to 
the mounting plate by a motion translator defining rack and gear 
arrangement. 
The improved focussing mechanism permits a wide range of axial movement of 
the mounting plate coupled objective lens without interfering with the 
camera components, including the pentaprism, requires no increase in the 
size of the camera, is reliable, rugged and efficient and is of great 
versatility and adaptability.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, particularly FIGS. 1 to 7 thereof which 
illustrated a preferred embodiment of the present invention, the reference 
numeral 2 generally designates an objective lens which is equipped with a 
focussing ring 4, diaphragm setting ring 6, a transmission lug 6a 
extending rearwardly from diaphragm setting ring 6 for the transmission of 
a diaphragm aperture value preset by manually operating diaphragm setting 
ring 6, and a diaphragm preset pin 8. 
A camera body 10, to which objective lens 2 is replaceably mounted, 
includes a pentaprism portion 10a, a film advancing lever 12, a shutter 
speed setting dial 14, a shutter release button 16, a film speed setting 
dial 18, a rewind knob 20 and a cell chamber 22 which also serves as a 
hand grip. Displayed on the top surface of shutter speed setting dial 14 
is a scale of numerals corresponding to shutter speed and a mark "A" for 
automatic shutter speed control. With a numeral on the scale set to index 
14a, a shutter mechanism (not shown) operates at a shutter speed 
corresponding to the set numeral. With mark "A" set to index 14a, 
photography in a diaphragm priority automatic shutter speed control mode 
is established. Moreover, provided beneath pentaprism portion 10a at the 
front of camera body 10, is a fixed housing 24, which is connected through 
a link assembly to a lens mount 26, on which objective lens 2 is 
interchangably mountable, as shown in FIG. 2. Lens mount 26 is box shaped 
and open at its rear and top and slidably telescopes into fixed housing 24 
and includes rearwardly projecting bottom and side walls at the rear of 
lens mount 26 which extend along inside the bottom and sides of fixed 
housing 24, the inner surfaces thereof overlapping the outer surfaces of 
lens mount 26. The top surface of lens mount 26 is connected to fixed 
housing 24 by means of an accordion wall or collapsible bellows 38, so 
that lens mount 26 is joined to fixed housing 24 for external light 
shielding even when moved along the optical axis. Mounted on the front 
wall of lens mount 26 are flange ring or annulus 26a of lens mount 26, 
lens-lock release button 27 which unlocks an objective lens when it is to 
be removed, and transmission ring 28 with interlocking lug 28a which 
interlocks with transmission lug 26a when objective lens 2 is mounted on 
lens mount 26 to thereby transmit the diaphragm aperture value preset by 
the objective lens to mechanism in the camera body 10. 
A changeover switch 30 is arranged on the front face of camera body 10 and 
is manually operable and connected and designed to energize a motor, as 
hereinafter described, for shifting lens mount 26 along the optical axis 
when index 30a on switch 30 is set to a mark "N" and for retracting lens 
mount 26 along the optical axis when index 30a is set to mark " ". When 
index 30a is set to mark ".", the motor is stopped to cease the movement 
of lens mount 26. FIG. 1 shows the condition of lens mount 26 in its fully 
retracted position along the optical axis. 
Disposed within the camera body 10 are a movable mirror 32, a mirror box 34 
and a diaphragm preset ring 36. Diaphragm preset ring 36 is movable along 
the optical axis integrally with lens mount 26 so that it is maintained in 
engagement with diaphragm preset pin 8 of objective lens 2, when lens 
mount 26 is shifted to any position within its overall range of shifting 
along the optical axis. Diaphragm preset ring 36 is rotated clockwise in 
response to the shutter release operation to permit the rotation of preset 
pin 8 which is urged to follow diaphragm preset ring 36 and to stop down 
the diaphragm mechanism. 
FIG. 2 shows the condition of lens mount 26 advanced along the optical axis 
from its fully retracted position as shown in FIG. 1. Referring to FIG. 2, 
the contractable bellows or accordian wall 38 connects fixed housing 24 
and lens mount 26 for external light shielding, the bellows being provided 
only on the top side thereof. The bottom and sides of the bellows or 
contractable conduit are defined by the fixed housing 24 and lens mount 26 
which overlap for external light shielding. Consequently, even when lens 
mount 26 is shifted along the optical axis, as described later, fixed 
housing 24 and lens mount 26 are always connected together to shield 
external light, a light tight expandable chamber being established between 
housing 24 and lens mount 26. X-shaped link assemblies 40, 41 and 42, as 
best seen in FIG. 7, are provided between fixed housing 24 and lens mount 
26, and are longitudinally expandable or extendable along the optical 
axis, each link assembly moving in a plane parallel to the optical axis. 
These link assemblies are provided on the bottom and sides of fixed 
housing 24, not on the top side thereof, i.e., not near pentaprism portion 
10 a since this would restrict or limit the positioning of the pentaprism, 
due to the provision of a link assembly on the top side. It is to be noted 
that although link assemblies provided on the bottom and one side alone 
are sufficient, their provision along three quadrilateral surfaces, as in 
the present embodiment, increase the over rigidity and strength of the 
structure. 
With reference to FIGS. 3 and 4 which show the lens mount 26 in its fully 
retracted and advanced positions respectively, a light transmitting 
portion is formed in the center of movable mirror 32, on the rear of which 
is mounted an auxiliary mirror 32a for rotation therewith. With this 
construction, scene light passing through objective lens 2 is reflected on 
movable mirror 32 and is directed toward a viewfinder optical system 
comprising focussing screen 44, condenser lens 46, pentaprism 48 and 
eyepiece 50. Part of the scene light is transmitted through the center of 
movable mirror 32 and is reflected by auxiliary mirror 32a, and is 
directed toward a light receiving element 52 arranged at a position 
optically equivalent to the film surface for the detection of the focus 
condition. A light sensing or responsive element 54 for automatic exposure 
control is arranged at the upper rear face of pentaprism 48. Also shown in 
the drawings are shutter mechanism 56, film 58 and film pressure plate 60. 
The focus condition of objective lens 2 is detected by light responsive 
element 52 for the detection of focussing and is indicated within a 
viewfinder. As shown in FIG. 7, the output signal of light responsive 
element 52 is transmitted as an input to a focus detecting circuit 53, 
which detects an in-focus or out-of-focus condition which is displayed by 
LEDs 55,57 and 59 provided inside the viewfinder. When, in the case of the 
present embodiment, objective lens 2 is focussed closer than an object to 
be photographed, LED 55 is energized when the lens is focussed at a 
greater distance than the object, LED 59 is energized and when the object 
is in proper focus, LED 57 is energized. 
A motor 62 is selectively rotated in forward and reverse directions when 
changeover switch 30 is correspondingly manually operated. Motor 62 which 
is mounted in the camera body is connected through a pinion and gear 64 to 
a rack portion 66a, a slide or drive arm or lever 66. Slide arm 66 is 
restricted to only longitudinal movement parallel to the optical axis by a 
guide pin 68 carried by mirror box 34 and a guide shaft 70 slidably 
engaging an elongated longitudinal slot in side arm 66, as hereinafter 
described. Formed at the rear of side arm 66 is rack portion 66a, and the 
front end of side arm 66 is connected to the central connecting pivot 42a 
of link assembly 42. With the above construction, motor 62 is rotated to 
advance or retract slide arm 66 along the optical axis, whereby link 
assemblies 42, 40 and 41 are respectively expanded or contracted, so that 
lens mount 26 is correspondingly shifted along the optical axis under the 
guidance of the link assemblies. 
As shown in FIGS. 5 and 6 which illustrate lens mount 26 in its fully 
retracted and advanced positions respectively, a sprocket 72, a spool 74 
and a cell 76 are housed in and proximate grip 22. Cell 76 is a power 
supply source for motor 62 to move lens mount 26. A switch S is 
electrically transferred by manually operated changeover switch member 30, 
and is provided with one movable contact piece a and two fixed contact 
pieces b and c. When index 30a of changeover switch 30 shown in FIGS. 1 
and 2 is set to mark " ", contact pieces a and b of switch S are 
inter-engaged to deliver power from cell 76 to motor 62, which is thus 
driven to retract lens mount 26 along the optical axis to the condition 
shown in FIG. 5. On the other hand, when index 30a is set to mark "N", 
contact pieces a and c of switch S are inter-engaged, energizing motor 62 
to rotate in the reverse direction, whereby lens mount 26 is shifted along 
the optical axis toward its forwardmost position. 
As best seen in FIG. 7, a fixed mounting frame 78 is secured to mirror box 
34 by four inwardly directed pins 78a through 78d, and is of open topped 
approximately U-shaped configuration with a lateral bottom cross arm and 
vertical laterally spaced side arms laterally offset from the pentaprism. 
Furthermore, provided between fixed frame 78 and mirror box 34 is guide 
pin 70, engaging and guiding slide arm 66. Guide pin 70 also serves as a 
fastener to secure fixed frame 78 to mirror box 34. The respective side 
and bottom arms of fixed frame 78 are connected with the ends of the 
individual link bars in X-shaped link assemblies 40, 41 and 42 which are 
all expandable and contractable in directions parallel to the optical 
axis. A movable vertical rectangular base plate 80 is provided with a 
central circular opening and is provided along its side and bottom edges 
with rearwardly directed flanges 80a, 80b and 80c, to which the other ends 
of the link bars in the link assemblies are connected, respectively. In 
other words, the other ends of the link bars or levers of link assembly 40 
are rotatably connected to flange 80a, those of link assembly 41 to flange 
80b and those of link assembly 42 to flange 80c, respectively. 
Furthermore, formed on flanges 80a, 80b and 80c are rearwardly projecting 
tabs 80d and 80e and a tab 80f (not shown), to which lens mount 26 is 
bonded or secured by screws. Fixed to central connection pivot 42a of link 
assembly 42 is the front end of slide arm 66 which is longitudinally 
slidable parallel to the optical axis. When motor 62 is energized and 
driven through control circuit 82 by the manual operation of changeover 
switch 30, slide arm 66 is longitudinally moved parallel to the optical 
axis, whereby link assembly 42 is longitudinally expanded or contracted 
parallel to the optical axis, and link assemblies 40 and 41 are also 
expanded or contracted in directions parallel to the optical axis. 
Another flange member 26a is secured to four fastener pins 84a through 84d 
projecting forwardly from movable base plate 80. 
Provided between flange member 26a and movable base plate 80 are 
transmission ring 28, sliding resistor element 86 described hereinafter, 
lens mount 26 and diaphragm preset ring 36. Transmission ring 28 is 
rotatably supported between flange member 26a and lens mount 26, and is 
biased counterclockwise by a spring 88. Interlocking lug 28a formed on 
transmission ring 38 press engages transmission lug 6a of objective lens 
2, as shown in FIG. 1, whereby the angular position thereof is set. In 
addition, a sliding brush 28b is fixed to and projects rearwardly from 
ring 28, and is in slidable engagement with sliding resistor element 86 
fixed to movable base plate 80. With the above construction, rotated 
angular the position of transmission ring 28 is set depending on the 
rotated angular position of the diaphragm ring of objective lens 2, and in 
response thereto, a positional relationship is set between sliding brush 
28b and sliding resistor 86, whereby the present aperture value 
information of the objective lens is transmitted to an exposure control 
circuit (not shown) in the camera body in the form of a resistance 
responsive signal. 
Diaphragm preset ring 36 includes four circumferentially spaced peripheral 
slots respectively slidably engaged by pins 84a through 84d. Accordingly, 
diaphragm preset ring 36 is rotatable for the length of the peripheral 
slots, and is biased in a clockwise direction by a spring 90. Formed on 
diaphragm preset ring 36 is a rearwardly offset radially inwardly 
projecting lug 36a positioned so that it is engaged by diaphragm preset 
pin 8 of objective lens 2, when objective lens 2 shown in FIG. 1 is 
mounted on lens mount 26. Furthermore, diaphragm preset ring 36 is 
provided with arm 36b supporting tab 36a and extending rearwardly parallel 
to the optical axis, and a longitudinal slot 36c is formed in arm 36b. 
Slidably engaging longitudinal slot 36c is a pin 92a provided at the end 
of a diaphragm preset lever 92, the movement of which is controlled by a 
well-known diaphragm preset mechanism (not shown) located inside camera 
body 10. The lengths of arm 36b and slot 36c of diaphragm preset ring 36 
are set so that follower pin 92a of diaphragm preset lever 92 engages slot 
36c within the overall range of longitudinal movement of lens mount 26. A 
stop lever 94 engages diaphragm preset lever 92, to prevent the rotation 
thereof and disengages lever 92 in response to the shutter release 
operation to release the diaphragm preset lever from its stop condition, 
thereby allowing it to be rotated. With the above construction, the 
diaphragm of an objective lens is aperture presettable in the overall 
movable range of lens mount 26 by means of the diaphragm preset mechanism 
provided inside a camera body. Lens mount 26 is secured to tabs 80d, 80e 
and 80f of movable base plate 80. 
Considering now the operation of the improved mechanism described above, 
with the objective lens 2 being mounted on lens mount 26 of camera body 10 
and being focussed at infinity, the lens mount 26 is fully retracted along 
the optical axis as shown in FIGS. 1, 3 and 5. Under this condition, the 
objective lens is in focus when an object is located at infinity, and this 
condition is indicated in the viewfinder by the illumination of LED 57. 
Moreover, under the aforesaid condition, the objective lens is out of 
focus on an object at a close distance, and this is observed in the 
viewfinder with the illumination of LED 59. While looking through the 
viewfinder, a photographer sets index 30a of changeover switch 30 to mark 
"N". This energizes and drives motor 62 to expand or extend link 
assemblies 40, 41 and 42, whereby lens mount 26 with objective lens 2 
mounted thereon is guided and advanced by the link assemblies along the 
optical axis. While observing the focus condition displayed inside the 
viewfinder, the photographer sets index 30a of changeover switch 30 to 
mark "." when objective lens 2 is focussed on a desired object, i.e., when 
LED 57 lights up. This stops motor 62 and any further movement of lens 
mount 26 whereby their stop and focussed condition is maintained. 
When lens mount 26 is at a forward position and the focussing position of 
objective lens 2 is set at a greater distance than that of the desired 
object, LED 55 lights up inside the viewfinder, advising the photographer 
to retract lens mount 26 along the optical axis by setting index 30a of 
changeover switch 30 to mark " ". Thus, the focussing position of 
objective lens 2 is retracted toward the camera, and when it corresponds 
to the distance of the desired object, LED 57 momentarily illuminates to 
indicate the in-focus condition. At this time, the photographer sets index 
30a of changeover switch 30 to mark "." to stop the movement of objective 
lens 2. 
With shutter release button 16 then depressed, the diaphragm of objective 
lens 2 is stopped down to the preset diaphragm aperture value by means of 
a diaphragm preset mechanism, movable mirror 32 and auxiliary mirror 32a 
are retracted outside the photographic optical path, and thereafter 
shutter 56 is opened for the time set by shutter speed setting dial 14. 
With mark "A" on shutter speed setting dial 14 set to index 14a, diaphragm 
aperture information on objective lens 2 set by sliding resistor 86 and 
ring 28, film speed information set by film speed setting dial 18 and the 
light measurement information output at light responsive element 54 are 
transmitted as inputs to an automatic exposure control circuit, and the 
exposure time is controlled by the automatic exposure control circuit. 
Thus, in accordance with the embodiment of the present invention described 
above, focusing of objective lens 2 may be performed without using 
focusing ring 4, and focus control changeover switch 30 is arranged near 
shutter release button 16, thus allowing focusing and shutter release 
operations to be accomplished with one hand. In addition, all mechanisms 
necessary for focusing can be assembled into a camera body, and no 
focusing interlocking mechanism between the camera body and objective lens 
is required, resulting in a simple, inexpensive construction. Moreover, 
according to the present embodiment, the flange back of a camera is 
changeable by shifting lens mount 26 forward, whereby the closest 
photographic distance of an objective lens is further shortened by setting 
the shift of lens mount 26 to an appropriate length to make close-up 
photography without the use of an extension bellows or close-up ring. In 
addition, link assemblies 40, 41 and 42 are simple and compact in 
construction, yet strong enough to withstand high external forces, thereby 
assuring the movement and positioning of objective lens 2 along and 
coaxial with the optical axis. At the same time, the link assemblies 
require a minimum of applied force for their expansion and contraction and 
are capable of guidance over great lengths thereby minimizing the required 
output of the drive device such as a motor, whereby shifting over a longer 
length is efficiently achieved. 
It should be understood that while the mechanism of the present embodiment 
is constructed such that the drive device is driven in response to a 
manual operation to control the movement of the objective lens, the 
present invention is not limited thereto, and the drive device may be 
automatically controlled by a focus detection device. In this latter case, 
there are numerous known methods and devices available for focus 
detection. These include a method utilizing the space frequency of an 
image formed by an objective lens, that utilizing contrasts, that 
utilizing a split image, that utilizing the phase difference between the 
outputs of two light receiving elements disposed symmetrically to the 
optical axis behind the plane optically equivalent to the film plane by 
scanning such planes vertically to the optical axis using a grid or the 
like. 
When, moreover, a focus detection method detects a direction in which an 
objective lens may be moved for focusing a desired object, the rotation 
direction and speed of motor 62 are controllable based on the output of 
the focus detection device. With the above construction, changeover switch 
30 may be connected and employed as the main switch of the focusing 
mechanism. Furthermore, when the main switch is constructed and associated 
such that it is closed upon depression of shutter release button 16, 
focusing and photography are initiated by shutter release button 16, 
thereby requiring that shutter release button 16 only be depressed by a 
photographer. 
In addition, with the present embodiment, lens mount 26 is shifted 
forwardly and rearwardly along the optical axis in response to the forward 
and reverse rotations of motor 62. However, the improved mechanism may be 
so construed that link assemblies 40, 41 and 42 are biased toward their 
contracted conditions by springs, against whose influence lens mount 26 is 
shifted forward by the drive device, such as a motor, and lens mount 26 is 
retracted to its fully retracted position under the action of the springs 
after its disconnection from the drive devices. 
FIG. 8 illustrates another embodiment of the present invention, in which 
the above construction is achieved. The same reference numbers are used 
for members corresponding to those in the first embodiments in order to 
simplify the description. Springs 100, 101 and 102 are provided between 
the camera body and the respective pivoted intersecting point of paired 
link bars constituting each of the link assemblies 40, 41 and 42. These 
link assemblies are biased by springs 100, 101 and 102 in the direction of 
their contraction. In the present embodiment, an automatic focusing 
mechanism is provided for automatically focusing objective lens 200. The 
automatic focusing mechanism includes light receiving element 52, focus 
detection circuit 103, power supply source 104, start switch 105, motor 
control circuit 106 and motor 62 connected as illustrated. Motor control 
circuit 106 supplies power to rotate motor 62 when start switch 105 is 
manually closed externally of the camera, and cuts off power when 
receiving an in-focus signal from focus detection circuit 103 to thereby 
stop motor 62. On the other hand, focus detection circuit 103 receives a 
signal from light receiving element 52 to detect an in-focus or 
out-of-focus condition of objective lens 200, and sends an in-focus signal 
to motor control circuit 106 when objective lens 200 is focused on a 
desired object. Drive gear 107 drive coupled to motor 62 is connected 
through a one-way clutch mechanism 108 to gear 64. Clutch mechanism 108 
includes a first clutch gear or member 109 connected to drive gear 107 and 
second clutch gear or member 110 connected to gear 64, second clutch gear 
110 being axially movable together with gear 64 and biased by a spring 
(not shown) into engagement with first clutch gear 109. Clutch mechanism 
108 is constructed such that it transmits only the one-way rotation of 
drive gear 107, i.e., only the counterclockwise rotation of drive gear 107 
under the present embodiment, to gear 64. A clutch control lever 111 is 
rotated counterclockwise by an exposure completion signal, e.g., a signal 
responsive to the completion of travel of the trailing shutter curtain in 
the case of focal-plane shutter camera, and is reset to the position shown 
in FIG. 8 in response to the film advance operation. 
With the above construction, focusing is enabled by the external manual 
closing of start switch 105 first to be closed manually and when start 
switch 105 is closed, drive motor 62 is energized and rotates drive gear 
107 counterclockwise, which rotation is transmitted through clutch 
mechanism to gear 64, causing rack carrying slide arm 66 engaged therewith 
to be shifted along the optical axis. As slide arm 66 is shifted 
forwardly, link assemblies 40, 41 and 42 are expanded, causing lens mount 
26 to be linearly shifted along the optical axis at a fixed vertical 
orientation. On the other hand, focus detection circuit 103 detects the 
in-focus or out-of-focus condition by a signal from light receiving 
element 52 during the shift of objective lens 200, and generates an 
in-focus signal when objective lens is focussed on a desired object. With 
the input of an in-focus signal, motor control circuit 106 interrupts the 
supply of power to drive motor 62, which, in turn, stops. Upon the shutter 
being released when the infocus condition is reached, the film is exposed 
in the well-known manner, and after exposure with a lapse of a 
predetermined period of time, clutch control lever 111 is swung 
counterclockwise by a mechanism (not shown). With clutch control lever 111 
swung counterclockwise, gear 64 is retracted to a position out of 
engagement with rack portion 66a of slide arm 66. In addition, second 
clutch gear 110 formed integrally with gear 64 is moved to a position 
where it is disengaged from first clutch gear 109. With these clutches 
thus disengaged, the link assemblies are immediately contracted under the 
action of springs 100, 101 and 102, respectively, and lens mount 26 is 
rapidly shifted to its fully retracted position along the optical axis. 
With the film advance operation, clutch control lever 111 is rotated 
clockwise to reset gear 64 and second clutch gear 110 to the positions 
shown in FIG. 8 in readiness for focusing in the above manner. 
It is to be noted that a camera in accordance with the last described 
embodiment uses an objective lens 200 equipped with an electrical 
diaphragm mechanism unlike the camera according to the first embodiment. 
That is, objective lens 200 is provided with a common transparent 
electrode and ring-shaped transparent electrodes 201a.sub.1, 201a.sub.2 . 
. . 201an, each different in diameter and being concentrically arranged to 
overlap each other. Liquid crystal plate 201 is disposed between lenses 
202 and 203, and pins 204a, 204b, 204c and 204d electrically connected to 
these transparent electrodes, respectively, projected rearwardly from the 
rear edge of the lenses. On the other hand, movable base plate 80 is 
provided with contact pieces 205a, 205b, 205c and 205d which engage 
respective pins 204a, 204b 204c and 204d when objective lens 200 is 
mounted on lens mount 26. 
A diaphragm setting dial 206 is rotatably mounted on camera body 10, and 
the brush 207 of a slide resistor is connected thereto. A diaphragm 
control circuit 208 is arranged to actuate a corresponding number of 
contact pieces 205a through 205d in response to the adjusted resistance 
value of the slide resistor. Moreover, the diaphragm control circuit 
receives an exposure termination signal and a shutter release signal, 
thereby actuating the preceding contact pieces only when receiving a 
shutter release signal, and, in contrast, deactuating the contact pieces 
when receiving an exposure termination signal. 
Consequently, when the shutter is released with objective lens 200 mounted 
on lens mount 26, a selected plurality of the specified contact pieces 
205a through 205d are turned on in response to preset position of 
diaphragm setting dial 206. When an electrical signal applied to the 
contact pieces is transmitted as an input to objective lens 200 through 
signal pins 204a through 204d, the common electrode and the specified 
ring-shaped electrodes are energized, whereby the transparent electrodes 
form opaque rings. As a voltage is sequentially applied to the selected 
successive ring-shaped electrodes 201a.sub.1 through 201an, the round 
transparent portion in the center of liquid crystal plate 201 gradually 
decreases in diameter. This is equivalent to the diaphragm being stopped 
down. 
As described above, the camera of the present invention is constructed such 
that a lens mount on which an exchangeable objective lens is mounted is 
supported by expandable and contractable link assemblies on a camera body 
for shifting along the camera optical axis and the link assemblies are 
expanded and contracted by drive means provided inside the camera body, 
whereby the entire mount coupled objective lens is moved for focusing. 
Consequently, all the component parts required for the focusing mechanisms 
are assembled in the camera body, and as a result, it is possible to 
eliminate any special interlocking mechanism which interlocks the camera 
body and an exchangeable objective lens for focusing, thereby achieving a 
simple and inexpensive construction. In addition, as the objective lens 
need only be mounted on the lens mount, conventional interchangeable 
objective lenses may be employed, including objective lenses equipped with 
no focusing mechanism. Furthermore, the flange back of a camera is 
changeable by expanding the lens mount, and thus close-up photography is 
possible without using any special attachment for close-up photography, 
such as bellows or a close-up ring. Furthermore, with the mechanism of the 
present invention, link assemblies are provided to guarantee that the 
objective lens shifts along and is maintained coaxial with the optical 
axis. The link assemblies are simple and compact in construction and 
sufficiently withstand external forces so that the lens mount ensures the 
accurate shift of the objective lens parallel to the optical axis. In 
addition, the link assemblies require a minimum of applied force for 
expansion and contraction and are capable of guidance over a long distance 
so that great freedom of drive means and other mechanism design is 
available. 
Moreover, when a drive means is arranged for manual control, manual 
focusing is possible without turning a focusing ring. With the drive means 
automatically controlled in response to the output of a focus detection 
device, the earlier focusing operations are unnecessary. 
When a diaphragm control mechanism provided inside a camera body is 
arranged to control the diaphragm of an objective lens within the overall 
shift range of the lens mount, the diaphragm of the objective lens is 
controllable based on the information supplied from the camera, although 
the objective lens is shifted by the drive means to any desired position. 
In addition, when the link assemblies are disposed on the three sides other 
than that of the pentaprism side, the link assemblies are more durable 
under external forces so that the construction and positioning of the 
pentaprism and other camera components are not restricted. 
While there have been described and illustrated preferred embodiments of 
the present invention, it is apparent that numerous alterations, additions 
and omissions may be made without departing from the spirit thereof.