1988-03-30
1991-01-22
Mathews, A. A.
354288, G03B 1702
Patent
active
049874365
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention generally relates to apparatus for controlling the size of the image plane in a camera, and more specifically to apparatus for controlling the size of an image plane in a camera which includes a zoom lens. The present invention further relates to an apparatus for controlling the size of the image plane in a camera, which image plane size is restricted by an aperture.
2. Background Art
Generally, the size of an image plane in a camera is standardized in accordance with a predetermined standard, e.g., ISO or JIS (i.e., the Japanese Industrial Standard). The largest size of an image plane for 35 mm film is as follows: 24.8 mm.about.24.0 mm X (i.e., by) 36.8 mm.about.36.0 mm. The size of the image plane is restricted by the fixed aperture in conventional cameras. Such fixed apertures, which cannot be varied, have not been disadvantageous in present cameras, even those having a zoom lens. This is due to the fact that lens systems including a zoom lens are designed such that the size of the image plane cannot be influenced by the exit pupil, even where the exit pupil most closely approaches the image plane. In conventional cameras, the size of the image plane is restricted in the vertical direction by upper and lower inner rails which virtually come into contact with upper and lower edges of the film; and, in the lateral or horizontal direction, by an aperture formed in an aperture defining or restricting plane which lies in front of the inner rails.
The aperture defining plane is positioned in front of the inner rails in order to minimize damage which would otherwise be caused to the film by virtue of contact between the film and the inner rails. The distance between the aperture defining plane and the inner rails is generally about 0.5 mm. Such type of film plane size restriction mechanism is not disadvantageous in conventional cameras, e.g., even those having zoom lens systems, and therefore is capable of satisfying requirements such as the JIS.
However, it has been found that the size of the image plane can be larger than the standard in a zoom lens developed by the present applicant. This zoom lens has an exit pupil which very closely approaches the film plane at one extreme focal length, so that one or more rays of light will defract outwardly through the aperture. The aperture is restricted along its vertical extent by inner rails which come into contact with the film, and in a lateral direction by frames which have aperture defining surfaces spaced from the film plane, and which serve to define the aperture. Accordingly, because of the separation or spacing of the aperture defining surfaces from the film plane, enlargement of the image plane will occur in the lateral direction.
FIG. 17 illustrates the enlargement of the image plane in the lateral direction. In FIG. 17, Q represents the aperture defining surface, R represents the aperture formed in the aperture defining surface Q, and F represents the film plane. The actual image plane size of an image formed on film plane F, when exit pupil E is located at position L, and the actual image plane size of an image formed on film plane F when exit pupil E is moved to a position S closer to film plane F than position L, are defined by rays of light (a) and (b), respectively. As seen in FIG. 17, the actual size of the image plane is larger than the maximum standard size 36.8 mm when exit pupil E is in a position S which is closer to film plane F. There is a tendency for the exit pupil to more closely approach film plane F when the zoom lens increases magnification and when the size of the lens system is minimized. Conventional fixed apertures cannot solve this problem of enlargement of the actual image plane which arises when the exit pupil so closely approaches the film plane.
The film and, accordingly, film plane F, move within a tunnel-like space defined by and between a pressure plate 10, which ensures that the film plane will be flat, and inner rails 12, which restrict/abut the upper and lower edges of
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Asahi Kogaku Kogyo Kabushiki Kaisha
Mathews A. A.
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