Distance measuring equipment and camera

Photography – With exposure objective focusing means – focusing aid – or... – Reliability of focus/distance signal

Reexamination Certificate

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Details

C396S106000, C396S120000

Reexamination Certificate

active

06516150

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 semiconductor photo detector, such as an SPD element and a PSD element, is used. By way of example, Japanese Patent Application Laid Open Gazette Sho. 57-22508 discloses a system in which a PSD element is used to perform a focusing.
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 detecting surface of a semiconductor photo detector so that a photo-current is generated. A distance up to the camera subject is determined in accordance with the generated photo-current, and a photographic lens is moved to the distance thus determined. In this manner, a focusing is performed by the AF device, 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 semiconductor photo detector is smaller. Thus, S/N ratio of a signal representative of a photo-current is lowered, and it is difficult to exactly determine the distance up to the camera subject. 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, using a PSD element as the semiconductor photo detector, in such a manner that in case of the short distance there is adopted a focusing algorithm in which the ratio arithmetic value of photo-currents I
1
and I
2
outputted from the PSD element is integrated by a predetermined number of times so that a distance is calculated, and in case of the long distance there is adopted a focusing algorithm in which the addition value of photo-currents I
1
and I
2
outputted from the PSD element is integrated by a predetermined number of times so that a distance is calculated.
However, in the event that it is unclear as to whether a distance up to the camera subject is within an area of the short distance, it is a problem as to which one of the above-mentioned two algorithms is adopted to determine the distance.
According to the technology disclosed in Japanese Patent Application Laid Open Gazette Hei. 4-48208, arithmetic operations based on a plurality of focusing algorithms are simultaneously performed, and then it is decided as to which one of the operation results is adopted. In this case, the dedicated-arithmetic operation units are needed for the plurality of focusing algorithms, respectively. This is associated with a problem of increment of a circuit scale. Further, in this case, while the plurality of focusing algorithms are adopted, it is restricted to the use of plurality of focusing algorithms under such a condition that a photo sensor and a circuit unit directly relating to the photo sensing are in a certain fixed state. This is associated with a problem that a degree of freedom of selection of the focusing algorithms is low. For example, in the event that a detected signal derived by a photo sensor is amplified and transmitted to an arithmetic unit, there is a need to fix an amplification factor of an amplifier for amplifying the detected signal to a certain factor. Thus, it is impossible to adopt both the focusing algorithm wherein the amplification factor is set up to a lower factor and the focusing algorithm wherein the amplification factor is set up to a higher factor.
Alternatively, it is considered that an approximate distance, which is recognized by an operator of a camera through eye measurement, is taught to the camera. In this case, however, there is a need to provide an operation button and the like for performing such an operation, and the operation is troublesome per se. Further, it is considered that an operator forgets the operation and performs a photography. This is not preferable.
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 efficiently a greater accuracy of focusing without troubling an operator, and a camera incorporating thereinto such a distance measuring equipment.
To achieve the above-mentioned object, the present invention provides a first 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,
wherein said distance measuring equipment has a plurality of focusing algorithms for measuring a distance up to the target to be measured in distance, any one of the plurality of focusing algorithms is used to perform a first focusing, and a number of times of focusing is determined in accordance with the first focusing.
According to the first distance measuring equipment, any one of the plurality of focusing algorithms is used to perform a first focusing, and a number of times of focusing is determined in accordance with the first focusing. This feature makes it possible to perform a focusing with greater accuracy without troubling an operator.
To achieve the above-mentioned object, the present invention provides a second 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,
wherein said distance measuring equipment has a plurality of focusing algorithms for measuring a distance up to the target to be measured in distance, any one of the plurality of focusing algorithms is used to perform a first focusing, and a focusing algorithm to be used for a second focusing and subsequent focusing is determined in accordance with the first focusing.
According to the second distance measuring equipment, any one of the plurality of focusing algorithms is used to perform a first focusing, and a focusing algorithm to be used for a second focusing and subsequent focusing is determined in accordance with the first focusing. This feature makes it possible to perform a focusing with greater accuracy without troubling an operator.
For example, the embodiments, which will be described later, relate to an embodiment in which both the embodiment of the first distance measuring equipment of the present invention and the embodiment of the second distance measuring equipment of the present invention are compounded. According to such an embodiment, a sort of the focusing algorithm and the number of times of focusing are determined in accordance with a distance to be measured in such a manner that in the first focusing the focusing algorithm according to the ratio arithmetic procedure is used to determine focusing data, and in the event that the focusing data thus determined is sufficiently reliable, that is, in the event that the focusing data is involved in the short distance area wherein a value of a noise component included in the photo signal for focusing is relatively small, the subsequent focusing is not carried out

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