Focus adjusting device for camera

The present invention is to provide a focus adjusting device for a camera, particularly a focus adjusting device capable of fine adjustment of the position of the focal plane with ease. One of the characteristic features of the present invention is that the lens barrel is provided with an adjusting member such as a screw in screw-threaded relation thereto, so that all that is necessary to effect a fine adjustment of the initial position of the lens barrel relative to the camera body is to rotate the screw to adjust the length of that portion of the screw which projects outwardly of the lens barrel.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to focus adjusting devices and more particularly to 
a device for axially moving a lens barrel. 
2. Description of the Prior Art 
It is known to provide a lens barrel moving device in the form of a 
helicoid thread on the lens barrel. The arrangement of the helicoid thread 
groove in the lens barrel is, however, very difficult from the point of 
view of machining and the formation of the helicoid thread directly in the 
lens barrel gives rise to a problem in that when the lens barrel is 
axially moved, it is caused to rotate about the optical axis thereof 
simultaneously. For this reason, the conventional device for axially 
moving the lens barrel by the use of the helicoid thread necessitates a 
supplementary mechanism for constraining the lens barrel from rotative 
movement. This calls for a large increase in the complexity of the 
structure of the control device for the lens barrel and the bulk and size 
thereof. 
SUMMARY OF THE INVENTION 
With the foregoing in mind, an object of the present invention is to 
eliminate the above-described drawbacks of the conventional device and to 
provide a focus adjusting device using a cam ring in controlling the axial 
movement of the lens barrel and capable of performing a fine adjustment of 
the focus very easily. 
Another object of the present invention is to provide a focus adjusting 
device capable of performing a fine adjusting operation of the focus 
adjustment by adjusting the amount of projection of a screw-threaded in 
the lens barrel. 
These and other objects of the invention will become apparent from the 
following detailed description of an embodiment taken in conjunction with 
the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A focus adjusting device of the present invention will next be described in 
greater detail. FIG. 1. is an exploded perspective view showing the 
construction and arrangement of the main parts of the focus adjusting 
device of the present invention as applied to a photographic camera. In 
the figure, 1 is a casing of a mechanical mounting for a lens barrel; 2 is 
a distance adjusting member having an extension 2a for charging in 
engagement with a lever 13 when in a set position as shown in FIG. 1, a 
gear 2b engaging with a governor to be described more fully later, a gear 
2c engaging with a stop wheel, contacts 2d functioning as an actuator 
switch for a distance dependent signal processing circuit (not shown), a 
cam 2e for control of axial movement of the lens, a flash-auto cam 2f and 
a stop pawl lever charging cam 2g of FIG. 6. The distance adjusting member 
2 is rotatably fitted on a guide portion 1b of the casing 1. A spring 3 is 
tensioned between a pin planted on the above-described gear 2 b and a pin 
on the casing 1, urging the adjusting member 2 to turn in a 
counterclockwise direction. The governor 9 comprises a gear engaging with 
the gear 2b, an escape wheel and anchor and functions to maintain the 
speed of rotation of the adjusting member 2 at an almost constant level. 
The stop wheel 10 formed in unison with that of the gears which engages 
with the gear 2c rotates as the member 2 rotates. This stop wheel 10 has a 
protuberance formed in a portion of the outer periphery thereof and 
arranged to be engageable with a pawl 11c of the stop lever to be 
described later, so that rotation of the member 2 is stopped against the 
force of spring 3. 4 is a lens barrel holding a photographic objective 
lens 4a as shown in FIGS. 2 and 3. This lens barrel 4 has a carrier 4c to 
which is fixedly connected a guide shaft 4b in parallel relation to the 
optical axis thereof as shown in FIGS. 2 and 3. This guide shaft 4b is 
arranged to be axially movable past a guide hole 1a in the casing 1 and a 
guide hole 6a in a front base plate 6 fastened to the casing 1 by screw 
fasteners. This shaft 4b is urged to move in a direction indicated by the 
arrow (FIG. 1) by a spring 7 between a washer 4d fixed thereto and an 
abutment plate 8. 5 is a focus adjusting screw threaded in the carrier 4c 
of the lens barrel 4, and the amount of projection of the screw 5 from the 
carrier 4c defined by d (FIG. 3) can be varied by rotating the screw 5. 
Since the spring 7 urges the shaft 4b to move in the direction indicated 
by the arrow as has been mentioned above, the front end of the screw 5 is 
in abutting engagement on the cam 2e of the member 2 as shown in FIG. 4. 
The camming surface of the distance adjusting member 2 is configured to 
have three distinct sections, of which the first 2e' is made so steep that 
the load on the adjusting member 2 is lessened at the start of rotation 
from the initial position, and the second 2e" is made so gentle as to 
provide a preparatory stroke which does not contribute substantially to a 
distance adjusting operation. It is noted that just when the screw 5 
transits from the first to the second section, the contacts 2d are 
switched on to start power supply to the distance dependent signal 
processing circuit. This is because the processing circuit generally takes 
an adequate time before it is stabilized. The provision of the camming 
surface portion 2e" as creating the preparatory stroke operates to 
increase the accuracy and reliability of focus adjustment, as the distance 
detecting operation has been stabilized when the camming movement of the 
screw 5 transits from the second to the third surface portion 2e'". It is 
further noted that another advantage of the provision of the gentle 
camming surface 2e" is to make it possible to shorten the width of the 
adjusting member 2 and therefore, to facilitate the compactness of the 
camera. With such cam mechanism, as the adjusting member 2 rotates, the 
screw 5 is driven to move by the camming surface 2e, whereby the lens 
barrel 4 is axially moved forwardly with the resultant position of the 
lens barrel depending upon the amount of rotation of the adjusting member 
2, that is, the camera-to-object distance. 11 is a stop pawl lever with an 
armature 11b fixedly mounted at the tail end thereof as shown in FIG. 6, 
the head of which is configured as a pawl 11c. This lever 11 is provided 
with a leaf spring 11a and a hair spring 14 urging the lever 11 to turn in 
a counterclockwise direction. 12 is an electromagnet arranged upon 
energization to attract the armature 11b, whereby stop pawl 11c is 
maintained out of engagement with any one of the teeth of the stop wheel 
10. Since the stop wheel is provided with the protuberance 10a, as the 
object is located at infinity, when the processing circuit does not 
produce a detection signal in a time interval necessary for the 
protuberance 10a to come in contact with the stop pawl 11c, the adjusting 
member is stopped by the stop lever 11 in engagement at its pawl 11c with 
the protuberance 10a. The base plate 6 in addition to the above-described 
guide hole 6a has holes 6d for the shafts of the governor 9, and a tubular 
portion 6e on which a film speed presetting ring 20 is rotatably fitted. 
Next explanation is given to the focus adjusting operation of the focus 
adjusting device illustrated above. As has been mentioned above, the 
protuberance 10a of the stop wheel 10 is arranged so that when the 
distance dependent signal processing circuit produces no actuating signal, 
that is, when the object distance sensed is infinite or in a panfocus 
range, the adjusting member 2 gets stopped from further rotation by the 
pawl 11c of the stop lever 11. In this stopped position, therefore, the 
lens barrel 4 assumes the forward terminal end of axial movement which 
represents the infinitely distant position or pan-focus position (near 15 
meters). With the stop pawl 11c and the protuberance 10a left engaged with 
each other, when the adjusting screw 5 is rotated so as to adjust the 
amount of projection, d, thereof, the sharp image plane of the 
photographic lens 4a for the infinitely distant object can be made to lie 
in coincidence with the film plane. Thus, it is made possible to 
manufacture focus adjusting devices with the advantage that the fine focus 
adjustment can be made with very much ease. 
The operation of the mechanical mounting for the lens is as follows: The 
mounting mechanism is assumed to be previously set in the shutter cocked 
position of FIG. 1. Then, when a release button (not shown) is depressed, 
the latching lever 13 is taken out of engagement with the extension 2a, 
permitting the member 2 to turn in the counterclockwise direction under 
the action of the spring 3, while the camming surface 2e is pushing the 
screw 5. Since, as mentioned above, the screw 5 is threadedly fixed to the 
lens barrel 4, and since the guide shaft 4b is arranged to be slidingly 
movable in the axial direction, the lens barrel 4 is driven by the camming 
surface 2e to move forwards. On the other hand, the start of movement of 
the member 2 causes the contacts 2d to start current supply to the signal 
processing circuit (not shown). Then, as the member 2 turns in the 
effective focusing range, when a condition of sharp focus is detected, an 
actuating signal is produced and applied to the electromagnet 12, whereby 
the electromagnet 12 is deenergized. In more detail, the object distance 
is photoelectrically sensed, while simultaneously measuring the amount of 
rotation of the member 2. When the outputs of the light sensor and the 
position sensor coincide with each other, the duration of energization of 
the magnetic winding 12 is terminated. Then, the lever 11 is turned in the 
counterclockwise direction by the action of spring 14, whereby the stop 
pawl 11c is brought into engagement with one of the teeth of the stop 
wheel 10 to stop the stop wheel from further rotation. Since, as has been 
mentioned above, the gear on the stop wheel 10 meshes with the gear 2c on 
the member 2, when the stop wheel 10 is arrested, the member 2 no longer 
moves forwards, thus the focusing operation of the lens barrel 4 is 
completed. 
As has been described in greater detail, in the focus adjusting device of 
the present invention, when assembling the parts thereof, only adjustment 
of the amount of projection of a single member screw-threaded in the lens 
holder suffices to achieve the fine adjustment of the position of the 
sharp image plane. This screw-threaded member also serves as a cam 
follower for controlling the axial movement of the lens. Therefore, the 
control mechanism for the lens holder can be constructed in a very simple 
form with a great advantage to the focus adjusting device for cameras.