Photography – With exposure objective focusing means – focusing aid – or... – Reliability of focus/distance signal
Utility Patent
1999-05-11
2001-01-02
Perkey, W. B. (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Reliability of focus/distance signal
C396S121000
Utility Patent
active
06169855
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a distance measuring apparatus, and more particularly, to a passive distance measuring apparatus which does not emit light, such as infrared light, but instead utilizes ambient light to measure a subject distance and which can be used in, for example, a camera.
2. Description of Related Art
Some lens-shutter type cameras are provided with an autofocusing system provided with a passive distance measuring apparatus. This passive distance measuring apparatus includes a pair of image forming lenses (i.e., distance measurement optical system) and a pair of line sensors or light receiving sensors on which subject images are respectively formed through the pair of image forming lenses so as to calculate a subject distance based on triangulation. In cameras of this type, a photographing optical system, a finder optical system and the distance measurement optical system are provided which are independent of each other. In some cameras of this type, the distance measuring apparatus is constructed as a single unit, i.e., a distance measuring unit consisting of the pair of image forming lenses, the pair of line sensors each comprised of an array of a large number of light receiving elements (i.e., photodiodes) on which a plurality of subject images of a common subject are projected, and an arithmetic operating portion for calculating a subject distance based on triangulation in accordance with the data outputted from the pair of line sensors. In the distance measuring unit, the optical axis of the distance measurement optical system does not coincide with either the optical axis of the photographing optical system nor the optical axis of the finder optical system.
In conventional cameras of this type, in the case where the photographing optical system is a zoom lens and the finder optical system is a zoom finder whose magnification varies in accordance with the varied focal length of the zoom lens, the relationship among the finder view formed through the finder optical system, the AF frame which is observed in the finder view and the distance measuring unit will now be described.
When zooming is effected towards the telephoto extremity, a subject image observed in the finder view is magnified due to a variation in the magnification of the zoom finder. However, the distance measuring unit always receives on its pair of line sensors subject images of constant magnification due to the magnification of the pair of image forming lenses of the distance measuring unit being fixed, and not varied in accordance with the varied focal length of either the zoom lens or the zoom finder, and furthermore, the size of the AF frame does not change in the finder view. Due to this, on the telephoto extremity side, the focus measuring area indicated by the AF frame, superimposed on a magnified or close-up subject image in the finder view, becomes smaller than the actual focus measuring area determined by the light receiving area of each line sensor in the distance measuring unit.
Accordingly, there is a difference in size between the AF frame in the finder view and the light receiving area of each line sensor in the distance measuring unit. Due to this difference, in conventional cameras of this type, it is often the case that a subject or subjects, observed out of the AF frame, but close to the AF frame, are sometimes erroneously brought into focus through the distance measuring unit as a main subject or subjects, especially when the zoom lens is on the telephoto side- As a result, the main subject is blurry in the resulting picture.
Furthermore, in conventional cameras of the type in which the optical axis of the distance measurement optical system of the distance measuring unit is not aligned with the optical axis of the photographing optical system nor the finder optical system, the optical axis of the distance measurement optical system in the distance measuring unit and the optical axis of the photographing lens are not always arranged to be precisely parallel to each other in an assembling process. If so, a common subject may not always be captured at the same time by both the distance measuring optical system in the distance measuring unit, and the photographing lens. It is not necessary to adjust the position of the distance measuring unit in the case where a deviation from an optimum arrangement between the optical axis of the distance measurement optical system in the distance measuring unit and the optical axis of the photographing lens is small, i.e., within an acceptable limit. However, if the deviation falls outside the acceptable limit, it is necessary to adjust the distance measuring unit by moving or swinging it so that both the optical axes may be placed parallel to each other to eliminate the deviation. In an adjustment of this kind, the distance measuring unit is moved or swung mechanically relative to the camera body.
After the distance measuring unit has been moved or swung for adjustment, data outputted from the distance measuring unit is checked to find out if it corresponds to predetermined reference data. If the data does not correspond to the reference data, the distance measuring unit is readjusted. Therefore, the adjusting operation, in which the distance measuring unit is firstly moved and data is subsequently checked, has to be repeated until such a time that the checked data corresponds to the predetermined reference data, thus resulting in a troublesome, time consuming operation.
Furthermore, in conventional cameras where the camera has a macro photographing mode for close-up photography in which the optical axis of the distance measurement optical system of the distance measuring unit is not aligned with the optical axis of the photographing optical system nor the finder optical system, such that the optical axis of the distance measurement optical system of the distance measuring unit deviates from that of the photographing lens by a large distance in left and right directions of the camera, a deviation occurs between the two positions. In other words, the position of a light receiving area on the line sensor on which subject images are projected in regular photography where a distance of a subject located on the optical axis of the photographing lens beyond a predetermined distance from the camera is measured, and another position of a light receiving area on the line sensor on which subject images are Projected in macro photography for a close-up where a distance of a subject close to the camera is measured within a certain distance range. As a result, the AF frame in the finder view and the light receiving area of each line sensor of the distance measuring unit do not correspond to each other in macro photography, thereby the subject distance cannot be precisely measured.
In a known lens-shutter type camera which has an autofocusing system provided with a distance measuring apparatus including a pair of image forming lenses, a pair of left and right line sensors each comprised of an array of a large number of light receiving elements used to define a single light receiving area, and an arithmetic operating portion for calculating a subject distance based on triangulation in accordance with the data outputted from the pair of line sensors, so that the subject distance can be calculated areas. However, in the measurement of the subject distance using one light receiving area at each line sensor, as mentioned above, there is only one measurement of the subject distance to be effected, and hence, if no optimum value is obtained by the single measurement or calculation, no focusing can be carried out, thus leading to a missed photographic opportunity.
To solve this problem, it is also known to divide the light receiving elements of each line sensor into a plurality of blocks or groups (i.e., a plurality of light receiving areas), so that the subject distance can be calculated based on sensor data obtained from the pairs of corresponding light receiving areas of the line sensors. However,
Kosako Kosei
Nakahara Naoto
Sato Takuma
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Berstein P.L.C.
Perkey W. B.
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