JPS6217201B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an optical system used, for example, when photographing a cinemascope film or projecting a cinemascope film, and more specifically, to a converter used in conjunction with a reference lens of an 8mm cine camera. . For example, when projecting CinemaScope film using a normal projection lens (hereinafter referred to as master lens) with a projection angle of 6° to 7°, conventional methods are used to double the horizontal direction of the projection screen. As shown in FIG. 1, a unidirectional magnification converter (hereinafter referred to as a converter) composed of a cylindrical lens was placed in front of a master lens. In such conventional examples, in order to loosen the accuracy of optical axis alignment between the converter and the master lens, the focal lengths of the front and rear lenses of the converter are set large, and the converter is attached to the projector body via a fixture. It was installed and used. Increasing the focal length of the front and rear group lenses in this way means that the distance between the front and rear group lenses becomes longer, and the effective diameter of the lens becomes larger. The drawback was that the entire structure was large and heavy. This will be explained more specifically. Normally, the optical axis alignment accuracy between the master lens and converter is about ±0.2 mm at most, and eccentricity that does not significantly affect performance in a normal optical system is approximately
2′. Now, for example, in an 8mm cine camera,
If the focal length of the master lens is f _M =25.0 mm, then the focal length that can allow eccentricity of the converter rear group lens is f _B =0.2 mm/tan2'≈350 mm. For example, in the case of a cinemascope, the magnification of the converter is β=0.5, so the focal length of the front group of the converter is f _A =-0.5f _B =-175 mm. FIG. 1 shows a lens configuration diagram of this conventional example on an actual scale. In the figure, 1' is the front lens group,
2' is a rear group lens, 3' is a reference lens, and 4 is a film. It is completely impractical to add such a huge converter to an 8mm cine camera. SUMMARY OF THE INVENTION An object of the present invention is to provide a unidirectional magnifying projection lens that has a small effective diameter and a small focal length, and is therefore compact and lightweight in both the lens and barrel, and is suitable for portability. Hereinafter, an embodiment of the present invention will be described in the case of an 8 mm cine camera. In this embodiment, the focal length of the reference lens is f _M =
25.0mm, and the focal length f _B of the converter rear group is
It was set to 100.0mm. Table 1 shows the lens configuration of this example. In the table, R is the radius of curvature (mm), D is the distance from the surface to the next surface (mm), N is the refractive index of the material in front of the surface, and ν is the ν of the material in front of the surface. The value φ indicates the effective diameter (mm) of the lens surface, and the subscripts are numbers sequentially assigned to the lens surface from the front. As is clear from Table 1, the effective diameter of the front lens group of the converter is φ ₁ = 28.0 mm, and the total length of the converter lens barrel is

[Formula] became. FIG. 2 is a lens configuration diagram drawn at the actual scale based on the design data in Table 1. In the figure, 1
2 is a front group lens of the converter, 2 is a rear group lens of the converter, both of which are cylindrical lenses, 3 is a reference lens, and 4 is a film. According to the present invention, for example, in the case of an 8 mm cine camera, the lens diameter of the converter can be reduced compared to the conventional example.
The size has been reduced to less than 1/2, and the length of the converter lens barrel is approximately
The weight of the converter lens is reduced to 1/3 and the weight of the converter lens is approximately 1/8.
The weight of the converter lens barrel has been reduced to approximately 1/12. Note that, as shown in FIGS. 3 and 4, various aberrations are well corrected.

[Brief explanation of the drawing]

FIG. 1 is a diagram of a lens configuration of a conventional example, and FIG. 2 is a diagram of a lens configuration of an embodiment of the present invention. Figures 3 and 4
The figures are aberration curve diagrams of the embodiment of the present invention, in which FIG. 3 shows various aberrations in the vertical direction, and FIG. 4 shows various aberrations in the horizontal direction. 1...Converter front group lens, 2...Converter rear group lens, 3...Reference lens, 4...Film.

【table】

【table】

Claims (1)

[Claims] 1. Consisting of two front group lenses and two rear group lenses, each of the above lenses is a cylindrical lens having magnifying power in only one direction, and the radius of curvature R of each lens surface is The distance D from the lens surface to the next surface,
A unidirectional magnifying projection lens in which the refractive index N of the substance in front of the lens surface and the ν value of the substance in front of the lens surface are values listed in the table below. 【table】