Optical: systems and elements – Prism
Reexamination Certificate
1999-01-12
2001-03-06
Shafer, Ricky D. (Department: 2872)
Optical: systems and elements
Prism
C359S834000, C396S384000, C396S147000, C396S148000
Reexamination Certificate
active
06198581
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a prism of a finder which is used in a camera, in particular a finder prism which is provided with a shoulder portion so that lines are formed so as to be visible within the field of view of the finder.
2. Description of the Related Art
Conventionally, a finder of a camera is formed with some in-finder information formed on itself, such as automatic focus target marks and short range correction marks. Such marks are formed by virtue of special lines formed in predetermined positions on a surface of a certain plate-like element.
A commonly used means for forming such in-finder information has been disclosed in Japanese Patent No. 2629690, which teaches that desired lines may be directly formed on a glass plate (i.e., a reticle) by means of an etching treatment.
Under the above-mentioned condition, however, since lines are formed on a glass plate by means of an etching treatment, when light passes therethrough, some problems occur which are associated with the depth of the etching treatment. Namely, when light passes therethrough, the reflectance from the surface of the glass plate will be different from the reflectance from the etched portions. As a result, it will appear to a person using the finder as if each single line is instead two lines.
In order to solve the above problem, Japanese Patent Publication 5-22890 has disclosed an improved finder prism in which the cross sections of convex portions (i.e., protrusions) and the cross sections of concave portions (i.e., grooves) are semi-circular, and the surfaces of the convex and concave portions are made to include a light dispersing structure.
However, when the cross sections of the convex portions and the concave portions are made into generally semi-circular shapes the corresponding manufacturing process becomes too complex, and thus the production cost is high.
Further, since the cross sections of the convex portions and the concave portions are substantially circular and since it is these cross sections that are then etched so as to be made visible to the user, it becomes difficult to avoid a problem of the width of the lines being large.
BRIEF SUMMARY OF THE INVENTION
A first object of the present invention is to provide an improved finder prism in which lines are directly formed on a prism, and said lines are made so as to have a narrow width. A second object of the invention is to enable the prism
1
to be manufactured at low cost.
In order to solve the above problems, according to the present invention, there is provided a finder prism, located between an objective lens and an ocular lens, adapted to transmit an image of an object to a camera user under a condition where an automatic focus target mark and a short distance correction mark are both visible when photographing an object. The prism is made of a resin, and a shoulder portion having a height either higher or lower than the face of the prism from which light from an object exits during a photographing process, thereby forming in-finder information such as an automatic focus target mark and a short distance correction mark on the prism.
Further, the difference in height of the shoulder portion relative to the exit face is in the range of 0.001-0.5 mm. Moreover, either a recessed portion or a protruding portion is formed on the above one surface of the prism by virtue of the formation of the above-mentioned shoulder portion.
With the present invention, it is possible to form in-finder information such as an automatic focus target mark and a short distance correction mark by directly forming lines on the prism. Further, when looking into the finder, the lines of in-finder information such as an automatic focus target mark and a short distance correction mark may be viewed as having an extremely narrow width.
REFERENCES:
patent: 2984145 (1961-05-01), Papke et al.
patent: 3094911 (1963-06-01), Reiche et al.
patent: 3421407 (1969-01-01), Hiruma
patent: 3575095 (1971-04-01), Keck
patent: 3900858 (1975-08-01), McCann et al.
patent: 4047222 (1977-09-01), Moskovich et al.
patent: 4064516 (1977-12-01), McLaughlin et al.
patent: 4106038 (1978-08-01), Kawakita et al.
patent: 4231649 (1980-11-01), Kimura et al.
patent: 4297020 (1981-10-01), Yamada et al.
patent: 4519685 (1985-05-01), Momiyama et al.
patent: 4634223 (1987-01-01), Ishii
patent: 5034764 (1991-07-01), Inabata
patent: 5095326 (1992-03-01), Nozaki et al.
patent: 5233475 (1993-08-01), Ohshita
patent: 5838504 (1998-11-01), Ichikawa et al.
patent: 5-22890 (1993-01-01), None
patent: 2629690 (1997-04-01), None
Inaba Osamu
Ohtake Katsuhiro
Shoji Masao
Arnold Bruce Y.
Arnold International
Fuji Photo Optical Co., Ltd.
Shafer Ricky D.
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