Exposure Meter

1. Field of the Invention

This invention relates to an exposure meter for cameras.

2. Description of the Prior Art

An exposure meter having the ability to display in a finder, a preset stop value or a shutter speed and employing a so-called point-follower, is known. In this construction, a pointer for an ammeter indicates, with the aid of an output from a photometering circuit, a shutter speed or a stop value which is a proper exposure value corresponding to the brightness of an external field, the sensitivity of the film etc., and a movable pointer to be moved in interlocking relationship with a stop ring of a camera lens or shutter dial are provided on the same scale plate.

It has also been known to provide a plurality of indicating elements, such as illuminating diodes instead of the ammeter, for an exposure meter, and in accordance with an output of a photometering circuit, one or two of the illuminating elements are turned on so as to indicate the state of photometry.

The two types of exposure meter mentioned above indicate in a finder a present stop value or shutter speed with a pointer-follow system using the indicating elements. Thus:

1. An exposure meter in which a plurality of indicating elements are arranged in a row facing the scale plate in the finder, some of the elements being selectively turned on in accordance with the output of the photometering circuit to indicate a stop value or shutter speed which represents a proper exposure, and in the vicinity thereof a pointer is provided which is movable in interlocking relationship with a stop ring of a lens or shutter dial of the camera; and

2. An exposure meter in which a plurality of indicating elements are arranged in two rows facing the scale plate in the finder, one row of which will be selectively turned on in accordance with the output of the photometering circuit so as to indicate a stop value or shutter speed which represents a proper exposure value, and the other row will be selectively turned on in interlocking relationship with the stop ring of the lens or shutter dial of the camera.

So far as the first type of exposure meter is concerned, it requires a complex interlocking mechanism to move the pointer in interlocking relationship with the stop ring or the shutter dial. In the second type of exposure meter, the interlock mechanism may be a simple switch, but the number of indicating element is very large resulting in high cost and lack of space economy.

I contribute by my invention an exposure meter by which I am able to overcome the foregoing difficulties and disadvantages and to provide an exposure meter able to perform the two functions of the prior art mentioned above, but with a simple structure and using the minimum necessary number of the indicating elements.

There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated.

There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures for carrying out the several purposes of the invention. It is important therefore that the claims be regarded as including such equivalent constructions as do not depart from the spirit and scope of the invention.

Specific embodiments of the invention have been chosen for purposes of illustration and description, and are shown in the accompanying drawings, forming a part of the specification, wherein:

FIG. 1 shows a circuit diagram of an embodiment of the present invention;

FIG. 2 shows an arrangement of the indicating elements in the finder of the camera; and

FIG. 3 shows a circuit diagram of a second embodiment of the invention.

In FIG. 1, which shows a circuit diagram of one embodiment of the invention, the photometry circuit 2 includes a photoelectric element (not shown) and calculates a proper exposure on the basis of the brightness of the external field, a preset stop value and a film sensitivity and makes selectively conductive one output terminal on n number output terminals 2-1, 2-2, 2-3, 2-4 . . . 2-n corresponding to the calculated shutter speed. The light illuminating diodes 4-1, 4-2, 4-3, 4-4 . . . 4-n are arranged facing the shutter speed scale 14 at lower side of the field of the finder, as shown in FIG. 2, and anode terminals of the diodes are commonly connected to the positive terminal of the electric source battery 1, while the cathode terminals thereof are connected to the corresponding output terminals 2-1, 2-2 . . . 2-n through corresponding protective resistors 3-1, 3-2 . . . 3-n . A changeover switch 5 consists of a brush 5a, collective element 5b, and taps 5-1, 5-2 . . . 5-n, the brush 5a moving in interlocking relationship with the shutter dial of the camera, so that one of the taps 5-1, 5-2 . . . 5-n, corresponding to the set shutter speed is selected to be connected to the collective element 5b. Such tap is connected to the junction of the cathode of a corresponding illuminating diode and its corresponding protective resistor. For example, the tap 5-1 is connected to the junction of the cathode of the diode 4-1 and the protective resistor 3-1. The collective element 5b is connected to the collector of the transistor 8 through the resistor 7. The emitter of the transistor 8 is connected to the negative terminal of the battery 1, and the base thereof is connected through a resistor 9 to the output terminal of an astable multivibrator producing a pulse signal of a definite period and consisting of inverters 10 and 11, resistor 13 and condenser 12 connected as shown.

According to the above described structure, when the camera is directed toward an object to be photographed after presetting the stop value of the lens and the sensitivity of the film, the photometry circuit 2 will turn on the illuminating diode corresponding to the proper shutter speed in response to the brightness of the object. If 1/125 second is the shutter speed for a proper exposure value, only the output terminal 2-4 of the photometry circuit 2 becomes conductive so that the illuminating diode 4-4 is turned on. Then the shutter dial is rotated to set the shutter speed to 1/500 second, the brush 5a of the switch 5 connects the tap 5-2 with the collective element 5b. Since the astable multivibrator consisting of the inverters 10 and 11 and the resistor 13 produces pulses of the definite period, the transistor 8 repeats ON and OFF with the same period. Consequently, the pulse current having the same period flows into the illuminating diode 4-2 through the resistor 7 and the switch 5, so that the diode 4-2 will be turned on and off to indicate in the finder the shutter speed being set by the shutter dial. In this instance, in the finder, the diode 4-4 is turned on and the diode 4-2 repeats on and off. By this means, the photographer can see that the shutter speed necessary to obtain the proper exposure value is 1/125 second and the presently set shutter is 1/500 second. Therefore, when the shutter speed dial is rotated to change the shutter speed from 1/500 second to 1/125 second, the brush 5a of the switch 5 will connect the tap 5-4 to the collective element 5b. At this time, the current flowing through the illuminating diode 4-4 is the current determined by the resistance of the protective resistor 3-4 and in addition to this current, the pulse current flowing therethrough via the resistor 7 due ot the transistor is overlapped. Therefore, in the finder, the diode 4-4 will be alternately turned on with the two intensities of brightness, respectively, one of which corresponds to the current determined by the protective resistor 3-4 and the other of which corresponds to the current determined by the resistor 7 in addition to the current due to the protective resistor 3-4. Thus, the photographer can verify that the shutter speed for obtaining the proper exposure indicated by the photometry circuit 2 coincides with the shutter speed being set by the shutter dial and this shutter speed is 1/125 second, which shows that the shutter speed set by the shutter dial is that giving the proper exposure.

The second embodiment will be explained with reference to FIG. 3. In the first embodiment shown in FIG. 1, the illuminating diode is turned on by the output of the photometry circuit 2, and is turned on and off by the output signal from the switch 5. In the second embodiment, the structure is reversely designed so that the diode is turned on by the output signal from the switch 5 and is turned on and off by the output of the photometry circuit. In FIG. 3, one of the input terminals of AND gate circuit 15-1, 15-2 . . . 15-n is connected to one of the output terminals 2-1, 2-2 . . . 2-n, and the other input terminal thereof is connected to one of the output terminals 16-1, 16-2 . . . 16-n of the pulse generating circuit 16, and the output terminal of the AND gate circuits is connected to one of the protective resistors 3-1, 3-2 . . . 3-n. The collective element 5b of the switch 5 is connected to the negative pole of the battery 1 through the resistor 7.

By this arrangement, only the AND gate circuit connected to the conductive output terminal of the photometry circuit 2 is operated and the illuminating diode connected to this AND gate through the protective resistor will turn on and off; and the terminal of the switch 5 corresponding to the manually set shutter speed is connected to the negative pole of the source 1 so that only the diode connected to this terminal will turn on.

In FIG. 2, the illuminating diodes are arranged facing the shutter speed scale 14. However, it is possible to overlap the diodes on the scale plate so that the scale plate can be seen by illuminating the diodes.

Further, in the above described embodiments the diodes indicate the shutter speed, but it is also possible to use diodes to indicate the stop value set by the stop ring and the stop value to obtain the proper exposure, or to use diodes to indicate the combination of the stop value and the shutter speed in case of a program shutter.

In case the camera has an automatic exposure control device and is provided with a switching device for enabling a manual set, the lighting of the illuminating diode will indicate the proper exposure stop value or the shutter speed when the exposure is automatically controlled, and the on and off operation of the diode will indicate the shutter speed or the stop value set manually when the exposure is switched to manual operation; and this will also indicate whether the exposure is automatically controlled or manually controlled.

As explained in the foregoing description, according to this invention, I contribute a simple structure using a minimum number of necessary indicating elements, the preset shutter speed or the stop value is indicated in the finder and the pointer-follow up function is performed. Moreover, by the use of illuminating diodes as the indicating elements, I provide strong resistance against mechanical shock, and the overall reliability of my exposure meter is greatly improved.

I believed that the construction and operation of my novel exposure meter will now be understood, and that the advantages thereof will be fully appreciated by those persons skilled in the art.