Photography – With exposure objective focusing means – focusing aid – or... – Having auxiliary illumination
Reexamination Certificate
1999-10-07
2001-02-13
Perkey, W. B. (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Having auxiliary illumination
C356S003040
Reexamination Certificate
active
06188844
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rangefinder apparatus for measuring the distance to an object to be measured; and, in particular, to an active type rangefinder apparatus suitably used in a camera or the like.
2. Related Background Art
In active type rangefinder apparatus used in cameras and the like, an infrared light-emitting diode (IRED) projects a luminous flux toward an object to be measured, the reflected light of thus projected luminous flux is received by a position sensitive detector (PSD), a signal outputted from the PSD is arithmetically processed by a signal processing circuit and an arithmetic circuit and then is outputted as distance information, and the distance to the object is detected by a CPU. In general, since errors may occur when the distance is measured upon a single light-projecting operation, light is projected a plurality of times so as to obtain a plurality of distance information items, which are then accumulated at predetermined intervals by an integrating circuit so as to be integrated and averaged.
In such a rangefinder apparatus, it is preferred that the period of each accumulating operation and the number of accumulating operations in the integrating circuit be set to values corresponding to the external light luminance. Namely, from the viewpoint of improving the accuracy in distance measurement, it is preferable that the period of each accumulating period be elongated when the external light luminance is lower than when it is higher.
SUMMARY OF THE INVENTION
However, the period of each accumulating operation set by the CPU is limited to integral multiples of a predetermined time (e.g., 2 microseconds) and cannot be set to an arbitrary time. Therefore, if the period of each accumulating operation and the number of accumulating operations in the integrating circuit are set to values corresponding to the external light luminance, then the integration time (=period of each accumulating operation×number of accumulating operations) may vary depending on the external light luminance. Hence, for accurately computing the measured distance value from the result of integration, it is necessary to carry out the computation in conformity with different converting expressions depending on the integration time. In this case, since a plurality of converting expressions are needed, the program in the CPU increases its size, whereby storage means such as electrically erasable and programmable read-only memory (EEPROM) and the like necessitate a larger storage capacity.
In order to overcome the problem mentioned above, it is an object of the present invention to provide a rangefinder apparatus which can compute the measured distance value from the result of integration according to a single converting expression even when the period of each accumulating operation and the number of accumulating operations in the integrating circuit are changed.
A first rangefinder apparatus in accordance with the present invention comprises: (1) light-projecting means for projecting a luminous flux toward an object to be measured; (2) light-receiving means for receiving reflected light of the luminous flux projected to the object at a light-receiving position on a position sensitive detector corresponding to a distance to the object, and outputting a signal corresponding to the light-receiving position; (3) arithmetic means for carrying out an arithmetic operation according to the signal outputted from the light-receiving means, so as to output an output ratio signal corresponding to the distance to the object; (4) integrating means for accumulating and integrating the output ratio signal, so as to output an integrated signal corresponding to the result of integration; (5) adjusting means for adjusting a period of each accumulating operation and the number of accumulating operations in the integrating means such that an integration time which is the sum of respective periods of the accumulating operations becomes a constant value; and (6) detecting means for detecting the distance to the object according to the integrated signal outputted from the integrating means.
In this rangefinder apparatus, a luminous flux is outputted from the light-projecting means toward the object to be measured, and is reflected by the object. The light-receiving means receives the reflected light at a light-receiving position on the position sensitive detector corresponding to the distance to the object, and outputs a signal corresponding to the light-receiving position. The arithmetic means arithmetically operates the signal outputted from the light-receiving means, and outputs an output ratio signal corresponding to the distance to the object. The integrating means accumulates and integrates the output ratio signal outputted from the arithmetic means, and outputs an integrated signal corresponding to the result of integration. According to the integrated signal outputted from the integrating means, the detecting means detects the distance to the object. Here, even when the period of each accumulating operation and the number of accumulating operations in the integrating means are changed according to the external light luminance, for example, they are adjusted by the adjusting means such that the integration time, which is the sum of respective periods of the accumulating operations, becomes a constant value. As a consequence, the distance to the object is detected by the detecting means in conformity with a single converting expression. In this rangefinder apparatus, it is preferred that, when adjusting the period of each accumulating operation so as to make it longer than a predetermined time, the adjusting means adjust the period of an accumulating operation within a range not shorter than the predetermined time, such that the integration time in the integrating means becomes the above-mentioned constant value.
A second rangefinder apparatus in accordance with the present invention comprises: (1) light-projecting means for projecting a luminous flux toward an object to be measured; (2) light-receiving means for receiving reflected light of the luminous flux projected to the object at a light-receiving position on a position sensitive detector corresponding to a distance to the object, and outputting a signal corresponding to the light-receiving position; (3) arithmetic means for carrying out an arithmetic operation according to the signal outputted from the light-receiving means, so as to output an output ratio signal corresponding to the distance to the object; (4) integrating means for accumulating and integrating the output ratio signal, so as to output an integrated signal corresponding to the result of integration; (5) adjusting means for adjusting a period of each accumulating operation and the number of accumulating operations in the integrating means such that an integration time which is the sum of respective periods of the accumulating operations lies within a constant range including a predetermined value; and (6) detecting means for detecting the distance to the object according to the integrated signal outputted from the integrating means in conformity with a converting expression for a case where the integration time in the integrating means is at the predetermined value.
This rangefinder apparatus operates substantially similarly to the first rangefinder apparatus except for the following points. Namely, in this rangefinder apparatus, even when the period of each accumulating operation and the number of accumulating operations in the integrating means are changed according to the external light luminance, for example, they are adjusted by the adjusting means such that the integration time, which is the sum of respective periods of the accumulating operations, lies within a constant range including a predetermined value. Then, for detecting the distance to the object in the detecting means, a converting expression for the case where the integration time is at the predetermined value is used. Preferably, in this r
Fuji Photo Optical Co., Ltd.
Leydig , Voit & Mayer, Ltd.
Perkey W. B.
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