Lens barrel automatic focalization device

A lens barrel automatic focalization device for a camera in which the camera body furnishes a focalization operational force in which the rotational resistance force produced by the focalization operation is made constant over various lenses so that the response time of the focalization operation is made uniform. The camera body includes a mount and a rotary member rotatably mounted on the camera body on a shaft perpendicular to the optical axis of the camera at the lower center portion of the mount. The focalization device includes a rotary member positioned so as to be rotatable by the rotary member of the camera body with the rotational force of the rotary member being coupled to a rotary cylinder having threads engaged with the threads of a movable sleeve or cylinder. The rotary cylinder is mounted within a stationary cylinder with ball bearings being provided therebetween. Rotational movement of the movable cylinder is restrained by a regulating cylinder fixed to the supporting cylinder and having guide pins which extend into corresponding longitudinal guide slots on the outer surface of the moving cylinder.

BACKGROUND OF THE INVENTION 
The present invention relates to a device which is provided for an 
interchangeable lens barrel whose focalization operation is automatically 
controlled through the camera body. 
In order to automatically carry out lens focalization a variety of devices 
have been proposed in the art which, for instance, are provided either 
outside of the lens barrel or integral with the camera. However, the 
conventional devices have not been found suitable for cameras which use 
interchangeable lenses as they require a relatively great focalizing force 
and accordingly are bulky in construction. Additionally the rotational 
resistance force involved in the focalizing operation is not uniform among 
different lenses. 
In order to alleviate these problems an object of the invention is to 
provide a lens barrel automatic focalization device in which a drive force 
transferring means which receives a focalizing operation force from a 
camera body is disposed at a position in the mount adapted to permit a 
lens barrel to engage with the camera body. It is desired that the device 
only minimally interfere with the optical paths of the optical system and 
that the rotational resistance force which is generated in the focalizing 
operation and is variable with different lenses is controlled so as to 
make uniform the response time of the focalizing operation. It is also 
desireable that the automatic focalization device be suitable for 
miniaturizing the drive source in the camera. 
SUMMARY OF THE INVENTION 
Accordingly, the primary and other objects of the present invention are met 
by a lens barrel automatic focalization device for a camera in which the 
camera body thereof produces a focalizing operational force with a rotary 
member for transfering the focalizing operational force rotatably mounted 
on the camera body on a rotary shaft which is perpendicular to the optical 
axis of the camera and which is disposed in the vicinity of an extension 
of a line connecting the centers of the long sides of an image viewed 
through the lens in a mount adapted to permit the lens barrel to engage 
with the camera body. In accordance with the invention, there is provided 
a lens mount, a supporting cylinder fixedly secured to the lens mount, a 
rotary member rotatably mounted on the lens mount which is adapted to be 
rotated by the rotary member of the camera body, a movable cylinder which 
is movable along the optical axis in accordance with movement of the 
rotary member, a rotary cylinder having one end face thereof formed with 
threads which are adapted to be engaged with threads formed on the movable 
cylinder, the rotary cylinder being supported rotatably around the optical 
axis by the supporting cylinder. 
Further in accordance with the invention, a plurality of male-threaded 
portions of the movable cylinder are cut away to form a plurality of 
surfaces each having a longitudinal axis disposed parallel to the optical 
axis and with a central portion of a female-threaded portion of the rotary 
cylinder cut away to form a cylindrical surface. The rotary cylinder, in 
preferred embodiments, is supported rotatably around the optical axis of 
the supporting cylinder by ball bearing members. The ball bearing members 
are provided in two sets of balls disposed respectively at forward and 
center portions of the rotary cylinder. There is preferably also provided 
a regulating cylinder which is mounted to the supporting cylinder with at 
least one guide pin extending from the regulating cylinder. Each of the 
guide pins is positioned in a corresponding longitudinal groove on the 
outer surface of the movable cylinder thereby to prevent its rotation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An automatic focalization device constructed according to the invention 
will be described with reference to the accompanying drawings. In FIG. 3, 
reference numerals 1-12 designate components of a lens barrel. Reference 
numeral 1 designates a movable cylinder which is adapted to hold an 
optical system and is movable along the optical axis by means of threads 
1a and 2a guided by guide pins 5 and straight grooves 1c which are 
parallel to the optical axis. Reference numeral 2 designates a rotary 
cylinder which has threads 2a engaged with the threads 1a and a sleeve 
part 2c cooperates with a drive force transferring rotary member 10 which 
receives a focalizing operational force from a drive rotary member 14 
which is provided in a camera body 22. 
In order to decrease the rotational resistance force between the threads 1a 
and 2a in the focalizing operation, several portions of the region of the 
movable cylinder 1 where the threads 1a have been formed are cut away in 
such a manner that plural surfaces 1b, which have a longitudinal axis 
parallel to the optical axis, are formed at equal intervals. The surfaces 
1b may if desired be trapezoidal in shape. Also, the central portion of 
the region of the rotary cylinder 2 where the threads 2a have been formed 
is cut away to form a cylindrical portion 2b. That is, only a necessary 
minimum contact area through the threads is provided between the two 
cylinders although the overall thread engaging length is retained. 
Accordingly, it is possible to reduce the size of the drive source which 
is provided in the camera body 22. Furthermore, as the rotational 
resistance force which is provided during the focalization operation and 
which varies in accordance with the optical system in the lens barrel can 
be controlled by suitably adjusting the size of the surfaces 1b and the 
cylindrical portion 2b, the response time of the focalization operation 
can be made uniform. 
Reference numeral 3 designates a supporting cylinder which supports the 
rotary cylinder 2 rotatably around the optical axis and which in turn is 
held integrally by a lens mount which connects to the mounting surface of 
the camera body (FIG. 1) in a well-known manner. Reference numeral 4 
designates a regulating cylinder which is fixedly secured to the 
supporting cylinder 3 by means of a fixing screw 8 which is inserted into 
the hole 3b of the supporting cylinder 3 and screwed into the tapped hole 
4a of the regulating cylinder. Movement straight along the axis of the 
rotary cylinder 2 is thus maintained when the rotary cylinder 2 is 
rotatably supported by the supporting cylinder 3. 
In order to decrease the frictional force which is generated when the 
rotary cylinder 2 is turned, the rotary cylinder 2 is held by balls 6 
provided between the inner wall of the supporting cylinder 3 and the end 
face of the regulating cylinder 4 and the rotation of the rotary cylinder 
2 is made adjustable by means of an adjusting screw 9 and with the aid of 
balls 7 which are rotatably inserted in the supporting cylinder 3. This 
also makes compact the drive source provided in the camera body and makes 
uniform the focalization response speeds for interchangeable lenses as the 
rotational resistance force which is generated in the focalization 
operation is varied. 
The aforementioned drive force transferring rotary member 10 is adapted to 
transfer the focalizing operation force from the camera body 22 as 
described before. It is made of an elastic material having a suitable 
hardness. The drive force transferring rotary member 10 is formed 
integrally with a bearing 11. The drive force transferring rotary member 
10 may also be provided with teeth in the form of a gear in which case the 
teeth should be formed so as to correspond with those 2c of the rotary 
cylinder 2. The drive force transferring rotary member is rotatably 
mounted on a shaft 12 by a screw 13. All of components 1-12 and the lens 
mount comprise the lens barrel. 
Reference numeral 14 designates a drive force rotary member which is 
provided in the camera body 22. The drive force rotary member 14 is made 
of an elastic material having a suitable hardness and constructed 
integrally with a bearing 15. In the case where the drive force 
transferring rotary member 10 is provided with teeth in the form of a 
gear, the drive force rotary member 14 should have corresponding teeth. 
The drive force rotary member 14 is rotatably mounted in the camera body 
22 upon a rotary shaft so that the drive force rotary member 14 and a gear 
16 are rotated as one unit. Furthermore, a gear 17 engaging the gear 16 
and a gear 18 are also mounted in the camera body 22 upon a second rotary 
shaft (not shown) so that the gears 17 and 18 are rotated as one unit. A 
gear 19 is so arranged that it is coaxial with a gear head 20 and a motor 
21 and is engaged with the gear 18. 
The preferred arrangement of the drive force transferring rotary member 10 
of the lens barrel and the drive force rotary member 14 of the camera body 
in the mount will be described. With reference to FIG. 1, the drive force 
rotary member 14 is rotatably mounted on a rotary shaft (not shown) at the 
lower portion of the mount of the camera body 22, the rotary shaft being 
perpendicular to the optical axis. Referring back to FIG. 3, in 
association with the drive force rotary member 14, the drive force 
transferring rotary member 10 is mounted on the shaft 12 in the lens 
barrel mount section with the shaft 12 perpendicular to the optical axis. 
That is, these rotary shafts are positioned on the extension of a line (L 
in FIGS. 2 and 3) connecting the centers of the long sides of a picture. 
The optical paths extending from an optical system E (only the last 
component thereof shown) to the short side A, the long side B and the 
diagonal line C of an image on an image forming plane D (or an image 
plane) are, in general, as shown in FIG. 2. As the drive force 
transferring rotary member 10 and the drive force rotary member 14 are so 
arranged that they do not interfere with the optical path extending to the 
short side, very little interference occurs with various optical systems. 
That is, the position of the rotary member 10 and 14 makes possible the 
use of the invention with nearly all interchangeable lenses. It goes 
without saying that, depending on the arrangement of the optical system of 
an interchangeable lens, it is not always necessary to position the rotary 
shafts of the drive force transferring rotary shaft 10 and the drive force 
rotary shaft 14 on the extension at the mount side of the lines connecting 
the centers of the long sides of the picture. That is, the rotary shafts 
may be positioned at points which are closer to the center of the long 
side and, on the extension, toward the mount side, of the line. 
The focalization operation with the invention will be described. When an 
instruction signal is outputted by a focalization detecting device (not 
shown) in the camera body 22, the motor 21 is rotated in a direction as 
specified to generate a focalizing operational force. The rotation of the 
motor 21 is transmitted through the gear head 20 and the train of gears 
19, 18, 17 and 16 to the drive force rotary body 14. As a result, the 
drive force rotary body 14 is rotated in the specified direction. The 
rotation of the drive force rotary body 14 is transmitted to the drive 
force transferring rotary member 10 to rotate the rotary cylinder 2. In 
this case, although the threads 1a are engaged with the threads 2a, 
rotation of the movable cylinder 1 is restrained by the guide pins 5 and 
the grooves 1c. Accordingly, the movable cylinder 1 is displaced along the 
optical axis to the correct focalization position. 
As is apparent from the above description, in the device according to the 
invention, the focalization operation force transferring means is provided 
at the position in the mount adapted to engage and disengage the lens from 
the camera body where it interferes very little with the optical paths of 
the optical system. Therefore, the device according to the invention can 
be applied to various optical systems, specifically, various 
interchangeable lenses. Furthermore, the rotational resistance force which 
is generated in the focalization operation is minimized. The size of the 
drive source in the camera body can be decreased over that required for 
use with prior art systems. In addition, the resistance force which is 
caused by the lens barrel during a focalization operation is made constant 
and accordingly the response time of the focalization operation is made 
uniform.