Photography – With exposure objective focusing means – focusing aid – or... – Ambient light compensating
Reexamination Certificate
1999-10-07
2001-02-13
Perkey, W. B. (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Ambient light compensating
C396S106000, C356S003040
Reexamination Certificate
active
06188842
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 central processing unit (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.
Also, in such a rangefinder apparatus, since the light received by the PSD includes not only the above-mentioned reflected light component but also a steady-state light component, the latter is eliminated as follows in order to take out only the reflected light component from the light received by the PSD. Namely, the luminous flux is projected from the IRED in a pulsing fashion, and the steady-state light component received by the PSD during the period when the luminous flux is not projected from the IRED is stored in the steady-state light eliminating capacitor in the signal processing circuit. Then, the steady-state light component stored in the steady-state light eliminating capacitor is subtracted from the reflected light component and steady-state light component received by the PSD during the period when the luminous flux is projected from the IRED, whereby only the reflected light component is outputted from the signal processing circuit.
SUMMARY OF THE INVENTION
However, as the steady-state light component stored in the steady-state light eliminating capacitor is subtracted from the reflected light component and steady-state light component received by the PSD, the voltage of the steady-state light eliminating capacitor gradually decreases. Consequently, the steady-state light component stored in the steady-state light eliminating capacitor gradually increases its error, and the output of the reflected light component outputted from the signal processing circuit also gradually increases its error. In particular, such an error would be greater when the external light luminance is higher. If such an error occurs, the accuracy in distance measurement will worsen.
In order to overcome the problem mentioned above, it is an object of the present invention to provide a rangefinder apparatus exhibiting an excellent accuracy in distance measurement even when the external light luminance is high.
The rangefinder apparatus in accordance with the present invention comprises: (1) luminance measuring means for measuring an external light luminance; (2) light-projecting means for projecting a luminous flux in a pulsing fashion toward an object to be measured; (3) light-receiving means for storing a steady-state light component received by a position sensitive detector when the luminous flux is not projected from the light-projecting means, receiving reflected light of the luminous flux projected to the object at a light-receiving position on the position sensitive detector corresponding to a distance to the object, and eliminating the stored steady-state light component, so as to output a signal corresponding to the light-receiving position; (4) 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; (5) integrating means for accumulating and integrating the output ratio signal, so as to output an integrated signal corresponding to the result of integration; (6) adjusting means for adjusting a period of each accumulating operation in the integrating means according to the external light luminance measured by the luminance measuring means; and (7) 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 in a pulsing fashion, and is reflected by the object. The resulting reflected light is received by the light-receiving means at a light-receiving position on the position sensitive detector corresponding to the distance to the object. The light-receiving means eliminates the steady-state light component received by the position sensitive detector when the luminous flux is not projected from the light-projecting means, 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, the period of each accumulating operation in the integrating means is adjusted by the adjusting means according to the external light luminance measured by the luminance measuring means. Specifically, the period of each accumulating operation in the integrating means is adjusted so as to become shorter when the external light luminance is higher than when it is lower.
In this rangefinder apparatus, the light-receiving means receives with the position sensitive detector, of the luminous flux outputted from the light-projecting means, the light reflected by the object to be measured, eliminates the steady-state light component, and outputs a signal corresponding to the light-receiving position. Upon eliminating the steady-state light component, the stored steady-state light component may decrease. The decrease in the steady-state light component is greater when the external light luminance is higher. In the present invention, however, since the adjusting means adjusts the period of each accumulating operation in the integrating means so as to make it shorter when the external light luminance is higher, the decrease in the steady-state light component during this period is small. Consequently, even when the external light luminance is higher, the accuracy in distance measurement would be excellent. Here, the period of each accumulating operation in the integrating means is set according to the external light luminance measured by the luminance measuring means, such that the decrease in the steady-state light component during this period lies within a permissible range.
Also, in the rangefinder apparatus in accordance with the present invention, the light-projecting means may project light in a pulsing fashion with a substantially constant duty cycle. In this case, the light-emitting intensity of pulses can be kept substantially constant without damaging the light-emitting device (e.g., infrared light-emitting diode) in the light-projecting means.
In the rangefinder apparatus in accordance with the present invention, the adjusting means may also adjust the number of accumulating operations in the integrating means such that the product of the period of pulse light projection in the light-projecting means and the number of accumulating operations is substantially constant among distance measuring actions. In this case, since the sum of respective periods of accumulating operations for each distance measuring action becomes greater when the external light luminance is lo
Fuji Photo Optical Co., Ltd.
Leydig , Voit & Mayer, Ltd.
Perkey W. B.
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