Photography – With exposure objective focusing means – focusing aid – or... – Optical detail with photoelement system
Reexamination Certificate
1999-03-03
2001-08-07
Perkey, W. B. (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Optical detail with photoelement system
Reexamination Certificate
active
06272291
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a focus detecting device adapted for a photographic camera, a video camera and an observation apparatus, or an optical apparatus using the focus detecting device, and more particularly to a focus detecting device arranged to divide the pupil of an objective lens (photographic lens) into a plurality of areas, to obtain a plurality of light distributions relative to an object image by using light fluxes passing through the divided areas and to detect the relative positional relationship of the plurality of light distributions, so that the focusing state of the objective lens can be advantageously detected for a plurality of areas within a photo-taking range.
2. Description of Related Art
Focus detecting devices of a light receiving type called an image-deviation type (phase-difference detecting type) utilizing a light flux passing though an objective lens have been popularly employed as automatic focus detecting devices for photographic cameras, video cameras and the like. Each of these image-deviation type focus detecting devices has optical means arranged on the image-plane side of the objective lens to obtain a plurality of light distributions relative to an object image by using light fluxes passing through the different areas of the pupil of the objective lens. Then, the relative positional relationship of the light distributions is obtained by a photo-electric conversion element composed of a plurality of pixel arrays. The focusing state of the objective lens is thus detected by using signals obtained from the photo-electric conversion element.
Further, some of the focus detecting devices of the image-deviation type area rranged to make a multi-point distance measurement having its distance measuring range cover not only a central area of the viewfinder field, i.e., a photo-taking range, but also some other areas located away from the central area in the vertical or horizontal direction. Each of such multi-point distance measuring focus detecting devices is arranged to have a plurality of focus detecting means, as disclosed, for example, in U.S. Pat. No. 5,005,041.
In the case of such focus detecting devices that are severely required to have a high degree of focusing precision, as in the case of a single-lens reflex camera, an image forming light flux obtained by the objective lens is led to a pair of reimaging lenses. Then, light distributions relative to an object image obtained by the pair of reimaging lenses must be very accurately formed on the pixel arrays of the photo-electric conversion element.
Generally, the arrangement for setting the distance measuring (focus detecting) areas not only in a central area of the photo-taking range but also in other areas located vertically and horizontally away from the central area necessitates use of many focus detecting members. The increase in number of focus detecting members incurs an increase in size of the focus detecting device. Particularly, the increase in size of a sensor chip used for forming the pixel arrays of the photo-electric conversion element causes an increase in cost.
Further, in the arrangement having a plurality of focusing detecting means, images formed on the sensor chip by reimaging lenses include not only images required for focus detection but also as many images as the product of the number of reimaging lenses and the number of focus detecting areas. That arrangement thus results in a drop in focus detecting accuracy caused by unnecessary light or in a further increase in size of the apparatus for eliminating the unnecessary light.
BRIEF SUMMARY OF THE INVENTION
It is an object of the invention to provide a focus detecting device which is arranged to be capable of accurately detecting a focusing state of each of a plurality of focus detecting areas located in vertical and horizontal directions within a photo-taking field, by appositely setting the various optical elements of focus detecting optical means disposed on the image-plane side of an objective lens (photo-taking lens), or an optical apparatus using the focus detecting device.
To attain the above object, in accordance with an aspect of the invention, there is provided a focus detecting device for detecting a focusing state of an objective lens, which comprises a field lens disposed adjacent to a prescribed image forming plane of the objective lens and having lens surfaces which differ in shape from each other correspondingly with a plurality of focus detecting areas, a reimaging lens disposed behind the field lens and having a pair of lens parts for forming a pair of light distributions for each of different pupils of the objective lens, and a light receiving sensor arranged to receive the pair of light distributions so as to detect the focusing state of the objective lens, wherein a first area of the field lens has a first field lens part having an optical axis which coincides with an optical axis of the objective lens, and a second area of the field lens which differs from the first area has a second field lens part having an optical axis which does not coincide with the optical axis of the first field lens part.
Further, in accordance with another aspect of the invention, there is provided a focus detecting device for detecting a focusing state of an objective lens, which comprises a field lens disposed adjacent to a prescribed image forming plane of the objective lens and having lens surfaces which differ in shape from each other correspondingly with a plurality of focus detecting areas, a reimaging lens disposed behind the field lens and having a pair of lens parts for forming a pair of light distributions for each of different pupils of the objective lens, and a light receiving sensor arranged to receive the pair of light distributions so as to detect the focusing state of the objective lens, wherein the plurality of focus detecting areas include first and second focus detecting areas which orthogonally intersect each other and a third focus detecting area which is disposed in parallel with and away from the first focus detecting area, the field lens includes a first field lens part which corresponds to the first and second focus detecting areas in common and a second field lens part which corresponds to the third focus detecting area, the reimaging lens includes a pair of first lens parts arranged to receive light from the first and third focus detecting areas and a pair of second lens parts arranged to receive light from the second focus detecting area, and a lens surface, on the side of the light receiving sensor, of each of the first lens parts of the reimaging lens has a curved surface convex toward the light receiving sensor.
The above and further objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in connection with the accompanying drawings.
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patent: 5822627 (1998-10-01), Moriyama
Canon Kabushiki Kaisha
Perkey W. B.
Robin Blecker & Daley
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