Fixed focus camera shooting hyperfocal distance

A fixed focus camera is arranged to shorten the minimum object distance for shooting by moving a lens section to a hyperfocal distance position. The camera is arranged to mount the objective lens system and the diaphragm member on the same tube, the lens system being formed to provide fixed focus, the diaphragm member being provided with a rotating member which is rotated to reduce light from the lens system, and to connect the tube to the body with a helicoid screw so that the rotation of the tube opens and closes the diaphragm member, and moves the lens system back and forth. Then, when the diaphragm opening is reduced by the rotations of the tube, the objective lens system is moved forward to a position where the subject is captured at a hyperfocal distance. This enables it to perform shooting at a hyperfocal distance, whereby the minimum object distance for shooting can be shortened when the diaphragm opening is reduced.

BACKGROUND OF THE INVENTION 
This application claims the priority of Japanese Patent Application No. 
8-156001 filed on May 27, 1996 which are incorporated herein by reference. 
1. Field of the Invention 
The present invention relates to a fixed focus camera, and, more 
particularly, to an arrangement of camera for adjusting focus with 
diaphragm opening in a micro-camera or the like. 
2. Description of the Prior Art 
Conventionally, a micro-camera (TV camera) called a small finger camara or 
the like is configured to have a single focal distance (fixed focus) 
because it should have a small size. However, when it has a variable 
diaphragm, the focal distance can be moved to near distance by reducing 
opening of the diaphragm. 
FIG. 5 shows an example of arrangement of a micro-camera. Disposed at the 
front end 1 of the camera shown in the figure is an objective lens system 
2 behind which a diaphragm member 3 opening of which can be varied is 
provided. The diaphragm member 3 is linked with a diaphragm adjusting ring 
4. A plurality of blades mounted on the diaphragm member 3 are moved by 
rotating the diaphragm ring 4, whereby the diaphragm opening 100 is 
varied. 
Mounted behind the objective lens system 2 is an imaging device, for 
example, a CCD (Charge Coupled Device) 5 as an imaging element the imaging 
plane (front plane) of which is positioned at the far end focal distance 
(.infin.) of the objective lens system 2. With such arrangement, if the 
minimum blur circle in the objective lens system 2 is assumed to have a 
diameter of 6 as shown in the figure, the depth of focus becomes a range 
of Do1 when the diaphragm opening 100 (amount) of the diaphragm member 3 
is at the maximum. Thus, a subject can be well captured if it is focused 
within this depth of focus. In addition, when the diaphragm opening 100 is 
the minimum, the depth of focus is within the range Dc1 on the principle 
that the depth becomes deeper when the diaphragm is reduced. A subject can 
be shot by the CCD 5 if it is focused within this depth of focus Dc1. 
Therefore, the shooting distance can be shifted to near distance by 
reducing the diaphragm opening 100. In this case, the minimum object 
distance (MOD) for shooting would be determined by the depth of focus Dc1 
or at the position NO shown in the figure. If exposure needs to be 
adjusted, it would be performed by controlling brightness of video signals 
obtained by CCD 5 or converting the illuminating light. 
BRIEF SUMMARY OF THE INVENTION 
However, the conventional micro-camera is frequently required to perform 
shooting at a short distance (close distance), and the minimum object 
distance MOD for shooting is demanded to be shorter. Particularly, since 
it is difficult to incorporate a focus lens in the objective lens system 2 
of such camera, it is requested to further shorten the minimum object 
distance assuming a fixed focus lens system. In addition, it is convenient 
also in a fixed focus camera such as a camera with a lens that shooting 
can be performed at a distance shorter than the current minimum object 
distance. 
The present invention is invented in view of the above, and intended to 
provide a fixed focus camera with a fixed focus lens system which can 
shorten the minimum object distance for shooting, whereby shooting is 
performed at a hyperfocal distance. 
To attain the above object, the present invention comprises a lens section 
formed to provide fixed focus, a diaphragm member provided with a rotating 
member which is rotated to reduce light from the lens section, and drive 
means for extending and retracting the diaphragm member in interlocking 
with rotation of the rotating member of the diaphragm member to move the 
lens section back and forth so that a subject is captured at a hyperfocal 
distance when the diaphragm opening is reduced. The hyper focal distance 
means a distance to the subject when the focus is adjusted so that the 
farthest point of depth of field extends to the infinite point. 
In addition, it is preferable to mount the lens section and the diaphragm 
member on the same tube, and to connect the tube to the body with a 
helicoid screw so that the rotation of the tube opens and closes the 
diaphragm member, and moves the lens section back and forth. 
With the above arrangement, when the diaphragm opening (amount) becomes 
larger, the objective lens system is positioned at the rear position so 
that the imaging plane of CCD is positioned at the shooting position, for 
example, at the focal distance of the lens system. Then, when the becomes 
smaller, the objective lens system is extended forward. In this case, the 
objective lens system is positioned at the hyperfocal distance, or at a 
position where the depth behind the depth of field is set at the infinite 
point. Moving the objective lens system to this hyperfocal point means 
that the depth of focus (depth of field) is extended independent of the 
diaphragm opening, so that the range allowing shooting is shifted to the 
near distance. Thus, the minimum object distance of shooting is made 
shorter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 (A) and (B) through FIGS. 4 (A) and (B) show the arrangement of the 
front end of a micro-camera as one embodiment of fixed focus camera. 
Components are described by referring to FIG. 1 (A) and (B)-FIG. 3. In the 
figures, the camera body 10 is provided with a CCD 11 as an imaging 
element. The CCD 11 is connected to a signal processing section through 
signal lines (not shown). The camera body 10 is screwed and connected to a 
separate front section (tube) 12 with a helicoid screw section 13. A male 
screw 13A is formed on the front end of the body 10, and a female screw 
13B screwed in the male screw 13A is formed on the rear end of the front 
section 12. The front section 12 is rotated by the connection of male 
screw 13A and female screw 13B. During the rotation, the front section 12 
is moved forward by a predetermined length L by the screw pitch of the 
helicoid screw section 13 as shown in FIG. 1 (B). The front section 12 is 
mounted with a fixed focus objective lens system 15 with a focal distance 
f which may consist of a plurality of lenses. A diaphragm member 16 is 
mounted behind the objective lens system 15. 
FIGS. 2 (A) and (B) show the arrangement of the diaphragm member 16. In the 
embodiment, as shown in FIG. 2 (A), a plurality of blades 17 (four blades 
in the figure) are supported by a shaft 18 for adjusting the opening 100 
of the diaphragm. Each blade 17 has a drive pin 19. 
A rotating plate 21 with an opening 21A is placed in parallel in front of 
the blade 17 as shown in FIG. 2 (B). The rotating plate 21 is formed with 
a guide groove 22 extending toward the center of circle in which groove 21 
the drive pin 19 on the blade 17 engages. Accordingly, when the rotating 
plate 21 is rotated to the right (or rotating the blade support to the 
left), four blades 17 move to the center so that the diaphragm opening 100 
is reduced. On the other hand, when the rotating plate 21 is rotated in 
the reverse direction, the four blades 17 move outward so that the 
diaphragm opening 100 is enlarged. 
In addition, a connecting rod 23 is mounted on the rotating plate 21, and 
inserted into a hole 24 formed in a cylindrical wall of the camera body 10 
so that it can move back and forth as shown in FIGS. 1 (A) and (B). 
Accordingly, the rotating plate 21 constrains the rotation of the front 
section 12 when it is rotated, whereby, in the diaphragm member 16 of the 
embodiment, the size of the diaphragm opening 100 would be variably 
controlled by rotating the support supporting the blade 17. 
Then, the CCD 11, the objective lens system 15 and the diaphragm member 16 
described above are arranged in the relationship as shown in FIGS. 4 (A) 
and (B). That is, while both FIGS. 4 (A) and (B) show the state where the 
diaphragm opening 100 is reduced to a predetermined value, the CCD 11 is 
placed so that the subject is imaged on the imaging plane at the focal 
distance (fixed focus) f of the objective lens system 15 as the diaphragm 
opening 100 is maximized by the blades 17 as in the case of FIG. 4 (A). 
The focal distance f of the embodiment is set at the far distance. 
In this case, the depth of field at the subject H is as shown in the 
figure. When the diaphragm opening 100 is reduced, the objective lens 
system 15 is extended forward so that the depth behind the depth of field 
is set at the infinite (.infin.) point. Therefore, the subject H is 
positioned at the hyperfocal distance. Thus, the depth of focus D can be 
made deeper as shown in FIG. 4 (B) by shooting the subject H at the 
hyperfocal distance. 
In other words, when FIG. 4 (A) is assumed to be a state where the diagram 
opening 100 is reduced by the conventional arrangement of FIG. 5, and FIG. 
4 (B) is assumed to be a state where the diaphragm opening 100 is reduced 
by the same amount by the present invention, the depth of focus Dc1 (a 
region contained in the minimum blur circle with the diameter 6) of FIG. 4 
(A) obtained by shooting at the ordinary focal distance becomes as deep as 
the depth of focus Dc2 of FIG. 4 (B) by setting the rearward depth at the 
infinite point. Generally, when the subject H is set at the hyperfocal 
distance, it is said that the forward depth is one half of the hyperfocal 
depth, and the depth of field contains a distance one half the hyperfocal 
depth to the infinite point. This means that it does not depend on the 
size of diaphragm opening 100, so that, when the diaphragm opening 100 is 
reduced, the depth of focal is made further deep. 
In addition, as shown in FIG. 3, marked on the outer surface of the front 
section 12 are a mark .infin. (far distance) in the rotating direction for 
maximizing the diaphragm opening 100, and a mark N (near distance) in the 
rotating direction for minimizing the diaphragm opening 100. 
The embodiment is arranged as above. Its operation is briefly described in 
the following. First, when the front section 12 is rotated until it stops 
at the far distance position (.infin.) as shown in FIG. 3, the diaphragm 
opening 100 is maximized with the blades 17 as shown in FIG. 1 (A), and 
the objective lens system 15 is retracted to be positioned at a position 
nearest to the CCD 11. At the moment, the relationship between the imaging 
plane of the CCD 11 and the objective lens system 15 is same as that of 
the prior art shown in FIG. 5, so that, at this far distance position, a 
subject at any distance where an object is imaged in the range of depth of 
focus Do1 can be imaged well. In this case, the shortest distance where 
shooting can be performed is the position of N1. 
Then, when the front section 12 is rotated to the near distance (N) from 
the far distance, the diaphragm opening 100 is reduced with the blades 17, 
and the objective lens system 15 is extended forward. When the front 
section 12 is rotated until it stops, the diaphragm opening 100 is 
maximized as shown in FIG. 1 (B), and the objective lens system 15 is 
positioned at a position nearest to the CCD 11 (only moved by a length L). 
At the moment, as described in conjunction with FIG. 4 (B), the rearward 
depth is set at .infin., the forward depth becomes one half the hyperfocal 
distance, and the depth of focus is within a range from one half the 
hyperfocal distance to .infin.. Then, at this near distance, it is 
possible to shoot a subject H at a distance where it is imaged within the 
depth of focus Dc2. The nearest distance where shooting can be performed 
is a position N2 which is closer than the position N1 FIG. 1 (B)!. That 
is, since the above range Dc2 is deeper than the conventional range Dc1 
shooting can be performed at a distance which is nearer than the 
conventional distance by that amount. Thus, in the embodiment, the minimum 
object distance (MOD) for shooting would be shorter than the prior art. 
While, in the above embodiment, the objective lens system 15 is 
incorporated with the diaphragm member 16, these components can be 
separately arranged to attain the same operation. In addition, while the 
objective lens system 15 can be constituted by a plurality of lenses, the 
diaphragm member 16 may be displaced in the lens group. 
As described, since the present invention is arranged in such a manner, 
when the diaphragm opening is reduced for a camera having a fixed focus 
objective lens system and a diaphragm member, the objective lens system is 
extended forward interlocking with rotation of the rotating member of the 
diaphragm member, shooting can be performed at the hyperfocal distance, 
whereby the minimum object distance for shooting can be shortened than 
that of the prior art by the focus control with the diaphragm. 
In addition, since the objective lens system and the diaphragm member are 
mounted on the same tube which is rotated by a helicoid screw to open or 
close the diaphragm and to move the objective lens system back and forth, 
opening or closing of the diaphragm and movement of the lens system can be 
performed with single operation of the tube, whereby the arrangement can 
be simplified.