1986-08-08
1987-09-08
Perkey, W. B.
354188, 354189, G03B 1910, G03B 2768
Patent
active
046920072
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a professional camera having a rail which forms the base of the camera and having a lens standard and an image standard which are displaceable independently of each other on said rail and on which there are arranged a lens support and image holder respectively which are swingable around at least one axis aligned transversely to the base of the camera, and having a ground glass which is adapted to be attached to the image holder and has at least two focusing lines extending parallel to the swivel axis of said holder.
For the simultaneous sharp focusing of two objects or parts of objects which are at different distances from the photographic lens of a camera, the image plane and/or the principal plane of the lens must be swung in such a manner that their extensions intersect the extension of the line connecting the objects to be photographed at a common point. Since the objects to be photographed are generally at a distance laterally as well as vertically from each other, the lens and image holders of a professional camera are swingable around two axes which are aligned perpendicular to each other and transverse to the base of the camera so that the above-mentioned imaging condition can be complied with. In this connection it must be borne in mind that the swiveling of the lens or image holder around an axis which does not pass through the center of the lens or the image holder produces a change in the optical distance between lens and image holders (the picture width) and that the swiveling around a vertical axis the swivel joint of which is located below the horizontal swivel axis produces a lateral displacement of the image on the image holder. In order to avoid, in particular, the first-mentioned error in focusing and the repeated refocusing necessary to correct it, it is known from Swiss Pat. No. 536 499 to calculate the swing of the image holder necessary for sharp focusing on two objects which are at a different distance away, from that displacement of the image standard along the base of the camera which is necessary for the sharp focusing of each of these objects and from the distance apart, measured at right angles to the swivel axis, of the two objects in the image plane or of the parallel extending lines passing through these imaged objects. The trigonometric formula used for this is, however, only valid if the image holder is at right angles to the base of the camera which determines the direction of displacement. This focusing error greatly limits the possibilities of use of the known focusing method and of the camera intended for the carrying out thereof, since the professional camera must be inclined to the horizontal for most photographs, for instance for architectural photographs in order to avoid so-called convergent lines or, in case of studio photographs, in order to establish preferred photographic angles. A simple calculation shows that, for instance, with an inclination of the camera base by only 15.degree., a distance (measured perpendicular to the swivel axis) of 20 mm between the two objects focused on the image holder and with a displacement of the image holder along the camera base by 40 mm, which is necessary for the sharp focusing of each of these objects, the swivel angle calculated in accordance with this formula gives an error of 11.5.degree.. This error becomes greater the more the base of the camera is inclined and the smaller the distance between the objects focused on the image holder relative to the displacement of the image holder along the camera.
Therefore, the object of the present invention is to create a professional camera in which the swing of the image plane necessary for the sharp focusing of two objects at different distances from the lens is calculated from the longitudinal displacement of the image standard on the camera base and the distance, measured perpendicular to the swivel axis, between the image points on a vertically standing image plane, regardless of the inclination of the camera base.
In accordance with the inventi
REFERENCES:
patent: 2301921 (1942-11-01), Willcox
patent: 3479945 (1969-11-01), Koch
patent: 3825938 (1974-07-01), Koch
patent: 4564277 (1986-01-01), Koch et al.
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