Photometric device for single-lens reflex camera

The disclosed photometric device measures light from an image formed on a focal plane and permits alterations in the portion of light distribution measured. The device has a hood at least partially disposed before a light receiving element which receives a light from the image formed on the focal plane. The light distribution measurement can be changed by moving the hood back and forth relative to the light receiving element.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a photometric device for a photographic camera of 
the so-called TTL photometric type adapted for measuring a light coming 
from an object to be photographed and passing through a photograph taking 
optical system and more particularly to a photometric device arranged to 
permit alterations in the light distribution measured. 
2. Description of the Prior Art 
Heretofore, to vary the measurement of the light distribution in a TTL 
(through-the-lens) photometry arrangement, either a plurality of optical 
systems were selectively arranged in front of a light receiving element 
and selectively used, or a condenser lens was moved on the optical axis 
thereof to permit an operation called zooming. Such known arrangements 
include, for example, photometric devices of the type using a plurality of 
optical systems as proposed in Japenese Laid-Open Utility Model 
Application No. SHO 53-121833, Japanese Laid-Open Patent Application No. 
SHO 53-98821 and Japanese Patent Publication No. SHO 47-49610. However, 
the use of a plurality of optical systems within a camera body is not 
desirable because they occupy considerable space. Besides, such an 
arrangement has limited capability in respect to the form of the range of 
measuring light distribution and thus generally does not permit arbitrary 
alteration of measuring light distribution. 
SUMMARY OF THE INVENTION 
It is a general object of the invention to provide a photometric device for 
a camera which obviates the abovementioned shortcomings of the 
conventional devices and permits varied measuring light distribution from 
the same photometric device. 
To attain this object, the device according to the invention is provided 
with a hood which is disposed in front of a light receiving element 
receiving a light flux coming from the image formed on an image plane to 
represent an object to be photographed. The hood is made movable back and 
forth relative to the light receiving element to partly restrict the light 
coming from the image of the object. 
The object and features of the invention will become apparent from the 
following description of an embodiment thereof taken in connection with 
the accompanying drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
Referring to FIG. 1 which shows an embodiment of the invention, there are 
provided a photograph taking optical system 1; a film surface 2; a mirror 
3 which is arranged if necessary; a light receiving element 4; and a hood 
5 of a tubular or square cylindrical shape. The hood 5 is arranged to be 
movable along a photometric optical axis A, for example, in the directions 
of arrows as shown in FIG. 1. 
With the embodiment arranged as described above, light from an object to be 
photographed coming through the photograph taking optical system 1 is 
imaged on the film surface 2. Then, diffused light is emitted from the 
film surface. A portion of the diffused light can be eclipsed by the hood 
5 and another portion of diffused light can be received by the element 4. 
The proportion of the eclipsed light to the received light can be changed 
by moving the hood 5 back and forth along the photometric optical axis A. 
In other words, variations of the position of the hood 5 in relation to 
the light receiving element 4 enables the photographer to continuously 
change the measured portion of the light distribution on the film surface. 
The reason for this can be understood from the illustrations of FIGS. 2 
and 3. 
In FIGS. 2 and 3 which illustrate different measuring light distribution, 
the mirror 3 is omitted for the sake of simplification of the 
illustration. With the light receiving element 4 and the hood 5 arranged 
in positions as shown in FIG. 2, the light distribution measured over the 
film surface 2 covers a range B1. 
Then, when the movable hood 5 is moved on the photometric optical axis in 
the direction of the arrow to bring it into the position shown in FIG. 3, 
the measuring light distribution becomes a range B2. This is called 
central area priority photometry. Thus, the measuring light distribution 
can be narrowed to put emphasis on the middle part of a picture in 
carrying out a light measuring operation. Since the position of the 
movable hood 5 is continuously variable, the measuring light distribution 
also can be continuously altered. 
Further, the measuring light distribution over the film surface can be 
altered as desired by varying the position of the hood 5 in a direction 
perpendicular to the photometric optical axis A. The varying operation on 
the hood 5 can be facilitated by providing a pin on the outside of the 
camera and by moving the pin. 
In this particular embodiment, the measuring light distribution is altered 
by moving the hood 5. However, the present invention is not limited to 
this arrangement and it is to be understood that the same effect is 
attainable in accordance with the invention by making the light receiving 
element 4 movable and the hood 5 stationary or by making both of them 
movable. 
Further, while the embodiment of the invention has been described to 
measure the light on the film surface, the invention is not only 
applicable to the film surface light measurement but also applicable in 
the same manner to the general arrangement of measuring a light on the 
focal plane of a single-lens reflex camera. 
As described in the foregoing, the photometric device according to the 
invention enables the photographer to continuously vary the measuring 
light distribution over the film surface. Therefore, it is an advantage of 
the invention that the device enables the photographer to selectively make 
averaged light measurements, make light measurements placing emphasis on 
the central area thereof or make mixed light measurements, so that a 
photometric operation can be accomplished in a satisfactory manner.