Photography – With exposure objective focusing means – focusing aid – or... – Having auxiliary illumination
Reexamination Certificate
2000-07-27
2002-02-05
Gray, David M. (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Having auxiliary illumination
C396S120000, C356S003040
Reexamination Certificate
active
06345153
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a distance measuring equipment for measuring a distance up to a target to be measured in distance in such a manner that light is projected and light reflected on the target and returned is detected, and a camera incorporated thereinto such a distance measuring equipment.
2. Description of the Related Art
Hitherto, there is widely spread a camera incorporating thereinto an automatic focusing (AF) device, which is generally referred to as an active type. Such an active type of automatic focusing device adopts a system for measuring a distance up to a camera subject in such a manner that an AF light projection unit and an AF photo detection unit are disposed at intervals of a predetermined base length, light is projected from the AF light projection unit to the camera subject, and light reflected on the camera subject is detected by the AF photo detection unit.
As a photo detector element for focusing, for example, a PSD element, is used. As an arithmetic device for performing an arithmetic processing in accordance with photo-current from the PSD element, for example, there is used an AF-dedicated photo detector IC for performing a ratio arithmetic processing.
To perform a photography using such a camera, first, a shutter button is subjected to a half-push operation. Then, light for focusing is projected from the AF light projection unit ahead of the camera, and light for focusing, which is reflected on the camera subject and returned, is detected on a detection surface of the PSD element so that a photo-current is generated. The photo-current thus generated is separated into two photo-currents (a photo-current at the short distance side and a photo-current at the long distance side) in accordance with the respective distances between a projection position on the detection surface of the PSD element and both ends of the detection surface. And signals representative of those two photo-currents are fed to the AF-dedicated photo detector IC. In the AF-dedicated photo detector IC, a ratio arithmetic processing is performed in accordance with the signals representative of those two photo-currents. A distance up to the camera subject is determined in accordance with a result of the ratio arithmetic processing, and an image taking lens is moved to the distance thus determined. In this manner, a focusing is performed, and then the shutter button is subjected to a full-push operation to perform a photography.
Generally, as a distance up to the camera subject is far, a photo-current from the PSD element is smaller. Thus, S/N ratio of a signal representative of a photo-current, particularly a signal of a long distance side, is lowered, and it is difficult to exactly determine the distance up to the camera subject by the AF-dedicated photo detector IC.
In view of the foregoing, Japanese Patent Application Laid Open Gazette Hei.4-48208 discloses a technology of enhancing accuracy in focusing for both the short distance and the long distance in such a manner that in case of the short distance for the camera subject, values wherein ratio arithmetic values of the photo-currents outputted from the PSD element are integrated by a predetermined number of times, are given as focusing data, and in case of the long distance for the camera subject, values wherein addition values (light quantity) of the photo-currents outputted from the PSD element are integrated by a predetermined number of times, are given as focusing data.
Further, in view of the foregoing, Japanese Patent Application Laid Open Gazette Hei.7-260475 discloses a technology of enhancing accuracy in focusing for both the short distance and the long distance in such a manner that control data, which are different for each camera, are written beforehand, and the optimum short distance side signal and long distance side signal are determined in such a way that the control data are utilized, when a focusing program is effected, to equally operate first and second amplifiers connected to a pair of output terminals of a PSD element, so that that the short distance side signal and the long distance side signal are fed to ports of a microcomputer for controlling a camera to perform an arithmetic operation.
However, according to the technology proposed in Japanese Patent Application Laid Open Gazette Hei.4-48208, there are individually needed a circuit for computing addition values and a circuit for computing ratio arithmetic values, and thus a circuit scale of a photo detector is enlarged. This causes the cost of the equipment or the device to be increased.
According to the technology proposed in Japanese Patent Application Laid Open Gazette Hei.7-260475, there is associated with such a problem that the number of input ports of the microcomputer is increased.
In view of the foregoing, it is considered that an AF-dedicated photo detector IC, which is capable of performing both the ratio arithmetic processing and the operating processing based on light quantity, is developed to adopt the same. In this case, however, it takes much cost for a development of the new IC per se. And in addition, the development of the new IC cannot bring about a merit in low cost caused by a mass production of the AF-dedicated photo detector IC performing only the ratio arithmetic processing. Thus, also in this case, there is associated with such a problem that the cost is increased.
This problem occurs also in the event that an SPD element having a divided detection surface is used as a photo detector for focusing, not restricted to a case where a PSD element is used as the photo detector for focusing.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide a distance measuring equipment capable of performing focusing with greater accuracy, suppressing the cost up, and a camera incorporating thereinto such a distance measuring equipment.
To achieve the above-mentioned object, the present invention provides a distance measuring equipment for measuring a distance up to a target to be measured in distance in such a manner that light is projected and light reflected on the target and returned is detected, said distance measuring equipment comprising:
a semiconductor photo detector element having a detection surface generating a photo-current upon receipt of irradiation of light;
a ratio arithmetic circuit, having two input terminals each for receiving associated one of current signals, for performing a ratio arithmetic operation in accordance with the current signals fed from the two input terminals;
a current source for generating fixed current signal; and
a first signal transmission path wherein the photo-current obtained through irradiation of light onto the detection surface of said semiconductor photo detector is lead to one input terminal of the two input terminals of said ratio arithmetic circuit and the fixed current signal from said current source to another input terminal of the two input terminals of said ratio arithmetic circuit.
According to the distance measuring equipment of the present invention, the photo-current generated on the detection surface of the semiconductor photo detector is fed to one input terminal of the two input terminals of the ratio arithmetic circuit, and the fixed current signal is fed to another input terminal of the two input terminals of said ratio arithmetic circuit, so that a ratio arithmetic processing is performed. This feature makes it possible to perform an arithmetic operation based on light quantity through adopting an algorithm referred to as a ratio arithmetic operation as it is. That is, it is possible to perform an arithmetic operation based on light quantity through adopting the conventional ratio arithmetic circuit as it is.
In the distance measuring equipment according to the present invention as mentioned above, it is preferable that said current source generates fixed current signal of an optional current value.
The use of such a current source makes it possible to control the focusi
Ishii Shuichi
Kotani Takaaki
Ushiro Seimei
Blackman Rochelle
Fuji Photo Film Co. , Ltd.
Gray David M.
Sughrue & Mion, PLLC
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