Patent
1980-01-22
1984-01-17
Corbin, John K.
350420, 350453, G02B 702, G02B 1308, G02B 1502
Patent
active
044261357
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a lens attachment used for optical instruments, such as photograph camera, motion-picture cameras, motion-picture projectors and enlargers, when they are employed to form wide-ranging images like those on a cinemascope.
DESCRIPTION OF THE PRIOR ART
When a main lens or lenses of an ordinary type (hereinafter referred to as the master lens) having a projective range of 6.degree. to 7.degree. is employed to form wide-ranging images upon a cinemascope for example, the common practice is to attach an extra lens unit to the master lens, the extra lens unit being commonly called a converter (hereinafter referred to as the converter). The converter consists of cylindrical lenses capable of forming horizontally widened images.
In such cases, however, the converter cannot be directly attached to the master lens because of the large effective diameter and weight of its rear member, thereby requiring the converter to be mounted on a special fixture adapted to be secured to the main instrument body by screws. Under this arrangement, a high degree of skill is required for securing precise centering of the lenses. In addition, attaching and detaching are time-consuming labor. To solve the difficulty of securing precise centering of the lenses through the converter to the master lens, it is previously arranged in the converter that each focal length of the front and rear members is relatively large; however, this means that the lenses in each member are accordingly spaced, thereby resulting in an increased effective diameter of the lenses. Thus, the converter as a whole unavoidably becomes large and heavy.
For a better understanding of the conventional converter system, it will be more particularly explained:
Normally, the tolerance in centering lens axes between the converter and the master lens is .+-.0.02 mm at maximum, and a permissible eccentricity is about 2' in which no appreciable degree of adverse effect will result. Now, let us suppose that an 8 mm motion-picture camera has a master lens having a focal length (f.sub.M) of 25.0 mm; then the permissible eccentricity of the rear member, in terms of focal length, will be: ##EQU1##
In the case of a cinemascope, the magnifying power of the converter (.beta.) may be 0.5; then the focal length of the front member (f.sub.A) will be: ##EQU2##
FIG. 1 shows the conventional arrangement of lenses on the actual scale, in which the front member 1', the rear member 2', the master lens 3' and a film 4 are respectively arranged. As evident from the drawing, the rear member 2' has a relatively large effective diameter compared with that of the master lens 3', and the distance therebetween is also disadvantageously large.
When forming wide-ranging images on a wide screen, the optical instrument requires the provision of cylindrical lenses capable of directional widening, and in order to achieve it, all the lenses must be properly centered, that is, the center of curvature of all the lens surfaces should line on the lens axis, so as to constitute a unitary optical system. However, it is difficult to properly combine these lenses in a mount especially when they are made of glass. In addition, when such a complete set of lenses including cylindrical lenses is attached to the main optical instrument with the use of screws or any other fastening means in the same manner as when a convertible lens or any other attachment is mounted, it may happen that wide-ranging images are projected on the wide screen in their tilting posture although the lenses are properly centered.
DISCLOSURE OF THE INVENTION
A feature of the present invention lies in that:
When the focal lengths of the front member and the rear member of the converter, and of the master lens are f.sub.A, f.sub.B and f.sub.M, respectively, a relationship among them can be established: that the above Formula (1) is satisfied. As a result, the diameter of the rear member is reduced substantially to that of the master lens, and additionally, the diameter of the front member
REFERENCES:
patent: 2752821 (1956-07-01), Cook
patent: 2932236 (1960-04-01), Delano
patent: 2956475 (1960-10-01), Harris et al.
patent: 3002427 (1961-10-01), Schafter et al.
patent: 3511557 (1970-05-01), Lindstedt et al.
patent: 3736049 (1973-05-01), Shimizu
patent: 3761162 (1973-09-01), Hall
Corbin John K.
Shinano Kikaku Co., Ltd.
Sugarman Scott J.
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