Camera with active optical range finder

In the disclosed camera, an optical arrangement projects substantially collimated light rays from a light emitter toward an object through an objective system in a finder, and a light receiver produces a signal that determines the relationship between the object and the camera by detecting the light from the objective system after reflection by the object.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to cameras, and particularly with view finders that 
also serve as light projection arrangements for distance measurements 
between the camera and an object. 
2. Description of the Prior Art 
Cameras with conventional automatic focusing mechanisms use triangulation 
systems in which imaging optics at one end of the base line cooperate with 
a movable mirror with other imaging optics at the other end of a base line 
such that moving the mirror to make the two images coincide allows one to 
obtain the distance to the object from the angle of the mirror. In another 
known system, a signal is emitted from the camera and the distance to the 
object is obtained from the angle of the signal returned from the object. 
Other than ultrasonic systems, such range finding mechanisms or automatic 
focusing mechanisms need two optical windows, one for projecting light and 
another for sensing returned light. Furthermore, aside from the window for 
a taking lens, one more window would be needed for an Alberda view finder, 
or two more windows for a mark system view finder. Thus, altogether four 
or five windows must be provided in autofocus blade-shutter cameras. 
Recently, very compact cameras have been brought on the market. The space 
on these cameras is so limited that it is difficult to provide four or 
five windows on their front surfaces. Moreover, when the base line of the 
automatic focusing device is made short, the accuracy of the distance 
measurement is decreased. Therefore, it is difficult to manufacture 
compact cameras with built in automatic focusing devices. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a view finder which 
also acts as a light projection optics for a distance measurement system. 
It is another object of the present invention to provide a view finder with 
autofocus optical system which needs less optical windows and smaller 
space, and is suitable for a ultra-compact camera. 
This invention is characterized in that the view finder and the light 
emitting optics have a common objective optics. The view finder consists 
of an objective optics and an eye piece arranged behind the objective 
optics. The light emitting optics for a distance measurement consists of 
the same objective optics, a reflecting mirror which is provided slantly 
between the objective optics, the eye piece, and a light source positioned 
outside the optical path of the view finder. 
A part of the light emitted from the light source is reflected by the 
reflecting mirror and directed through the objective optics toward the 
object to be photographed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be explained in detail in accordance with the 
drawings of the embodiments hereof. In FIG. 1, an objective lens 1 
consisting of a concave lens and an eye piece lens 2 consisting of a 
convex lens are arranged coaxially with the optical axis C1 of the view 
finder so as to constitute the so called Alberda view finder. Between the 
object lens 1 and the eye piece lens 2, a concave mirror 3 consisting of 
for example a dichroic mirror reflecting the infrared ray but allowing the 
transmission of the visible light is arranged slantly to the optical axis 
C1 of the view finder. The concave mirror 3 is preferably a portion of the 
ellipsoidal mirror which has a focal point P outside of the optical axis 
C1 and another focal point Q on the optical axis C1. At the point P above 
the concave mirror 3, a light source consisting of an infrared light 
emitting diode 4 for the distance measuring signal is arranged so as to 
emit the light toward the concave mirror 3. Further, a light sensing 
optics is arranged in parallel to the view finder optics, whereby the 
optical axis C1 of the view finder optics is almost parallel to that C2 of 
the light sensing optics. In the light sensing optics at the position of 
the focal point F of the light sensing lens 5, a light sensing element 6 
is provided. The light sensing element 6 is arranged near the focal point 
F in such a manner that angle .theta. of the reflected light beam L2 of 
the distance measuring signal is converted into a length .delta. from the 
optical axis C2 of the light sensing element 6. 
When the light is emitted through the window of the finder optics in this 
way, the distance can be measured as follows. The infrared light emitted 
from the light source 4 at the point P is reflected by the concave mirror 
3 and converged toward the point Q, whereby due to the negative power of 
the objective lens, the light is emitted outside of the objective lens 1 
as the distance measuring light beam L1, which is converged 2-3 m in front 
of the objective lens or parallel or diverged with small angle, for 
example about 5.degree.. The light beam L1 is reflected from the object 
and incident upon the light sensing optics. When the reflected light beam 
L2 is imaged at a position by .delta. distant from the optical axis C2 on 
the light sensing element 6, the distance D between the camera and the 
object can be obtained from the relation D=L.multidot.f/.delta., whereby 
.delta. is the distance from the optical axis C2 of the light sensing 
element 6, L is the distance between the optical axis C1 and C2, and f is 
the focal length of the light sensing lens 5. Hereby, because the concave 
mirror 3 reflects the infrared light but transmits the visible light, the 
object to be photographed can be observed through eye piece with enough 
visible light. Further, if the mirror 3 is made of very thin glass plate, 
the quality of the image to be observed is protected from deterioration. 
In the following, the second embodiment of the view finder optics will be 
explained with reference to FIG. 2. The arrangement of the present 
embodiment is almost similar to that of the first embodiment, whereby the 
concave mirror 3a is sandwiched between the transparent blocks consisting 
of glass or plastics. Though the function of the concave mirror 3a is same 
as that of the concave mirror 3 of the first embodiment, the concave 
mirror 3a can easily be produced in case of the present embodiment. 
Furthermore, by making the surface of the block to be semi-reflective for 
visible light, and providing the reflecting pattern, for example the 
distance measuring field mark or field frame, on or near the eye piece 
lens, such pattern can be observed superimposed in the object field. 
Because, through the eye piece lens 2, the vertual image of such pattern 
is observed with the aid of the reflection of the imaging beam by the half 
permeable mirror. Further, by giving a refracting power to a part of the 
block 7, it is possible to collect the light beam of the light source 4 
effectively to the objective lens 1. 
FIG. 3 shows the third embodiment. In case of the present embodiment, the 
objective lens 1b is supposed to have a positive power and instead of the 
above concave mirror 3a, a reflecting mirror such as a plane or a convex 
mirror is used. Hereby, in the same way as in case of the above concave 
mirrors 3 and 3a the reflecting mirror 3b reflects the infrared light but 
allows the transmittance of the visible light. Further, in case the 
objective lens 1b is a convex lens, by constituting the eye piece lens 
with a convex lens the object field is observed by the eye E of the 
photographer as an inverted image, so that it is necessary to convert the 
image to the erecting image by the optics corresponding to the eye piece 
lens. Further, it must be arranged a negative power lens in front of the 
light source 4 so as to balance the positive refracting power of the 
objective lens 1b. 
Below, the fourth embodiment will be explained with reference to FIG. 4. In 
the same way, as in case of the first embodiment, the objective lens 1d is 
a negative power concave lens and the eye piece lens 2 is a convex lens, 
whereby a plane mirror 3d is used as the reflecting mirror. Between the 
LED 4 and the plane mirror 3d, a convex lens 10 is provided, and the light 
beam emitted from the LED 4 is converged by the convex lens 10 and 
reflected by the plane mirror 3d. Then, the reflected convergent light 
beam is compensated by the objective lens 1d consisting of a concave lens 
into an almost parallel light beam L1, and is directed to the object in 
the same way as in case of the previous embodiment. 
As described so far, the present invention can reduce the number of the 
optical windows and realize a compact camera provided with an automatic 
focusing function by building the light projecting system in the view 
finder optics. Although the light beam for the distance measurement may be 
reflected and directed toward the objective lens by providing the 
conventional beam splitter with plane surface slantly across the optical 
axis of the view finder, the light beam emitted from the view finder is 
divergent due to ordinary negative power of the objective lens. 
On the other hand, in the present invention the divergent light beam 
emitted from the light source is converted into convergent beam with the 
refracting or reflecting optics having positive power arranged in the 
projecting optics. The convergent light beam is emitted from the view 
finder in the state of almost parallel beam by the negative power of the 
objective lens. Consequently, as the density of energy in the distance 
measuring beam is increased, the amount of light energy which is reflected 
from the object is also enough to detect the image position by the light 
sensing element. Further, because a part of the view finder optics is made 
use of as the distance measuring optics, i.e., the view finder optics and 
the light projection optics are coaxial, the position of the object whose 
distance is measured can easily be recognized in the finder field without 
parallax.