JPH1020383A - Soft focus attachment lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an attachment lens which is mounted on the front side of a normal photographic lens and adaptable to soft focus photographing. SOLUTION: The attachment lens 10 which is attached to the front side of the photographic lens 20 is constituted of two positive and negative lenses L11 and L12 made of materials having a mean dispersive power difference <=30%. The attachment lens 10 is freely attachably/detachably attached to the front side of an objective lens for the camera. Each lens face of both lenses L11 and L12 is formed to a shape so that the center of curvature radius may be positioned on an image field side, and a large spherical aberration is generated as the whole lens system of the camera under the combination of two positive and negative lenses.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soft focus photographic lens, and more particularly, to a soft focus attachment lens which can be detachably mounted on the front of a camera.

[0002]

2. Description of the Related Art Soft focus photography is used for portrait photography and the like. Conventionally, photography is carried out by a specially designed photographic lens or by placing a mesh screen on the front of a camera lens. Was being done.

[0003]

However, the use of a photographic lens dedicated to soft focus is a general demand that the use of this photographic lens is limited to soft focus and that soft focus photography is required less frequently. In view of this, there is a problem that a system requiring an expensive dedicated lens is not so preferable. Although the method of placing the screen in front of the lens is a simple method, the effect as a soft focus photograph is somewhat dissatisfied with only a decrease in the sharpness of the image.

The present invention has been made in view of such a problem.
It is an object of the present invention to provide a soft focus attachment lens that can be used as a detachable attachment to the front of a normal photographic lens, and that allows a soft focus photograph to be taken by mounting the lens.

[0005]

In order to achieve the above object, according to the present invention, there is provided an attachment lens attached to the front side of an objective lens of a camera, wherein the attachment lens is made of a material having an average dispersion ratio difference of 30% or less. The soft-focus attachment lens is configured to be detachably attachable to the front side of the objective lens of the camera by using the two positive and negative lenses. Each lens surface of these two lenses has a shape in which the center of the radius of curvature is located on the image field side, and a large spherical aberration is generated in the entire lens system of the camera in a state where these two lenses are combined.

A positive meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, a convex flat positive lens having a convex surface and a flat surface having a center of curvature on the image field side, and a flat and an image field From the plano-concave negative lens consisting of a concave surface having a center of curvature on the side, it is preferable to select and combine positive and negative lenses one by one to form a soft focus attachment lens consisting of the two positive and negative lenses.

Further, a lens having a positive refractive power is selected in a state where two lenses are combined as described above, and a soft focus attachment lens having a focal length of 800 mm or more can be used. Further, a soft focus attachment lens configuration in which the focal length becomes almost infinite when two positive and negative lenses are combined as described above may be employed.

Further, a soft focus attachment lens configuration having a negative spherical aberration and a weak negative refractive power in a state where two positive and negative lenses are combined as described above can be adopted.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. In general, a soft focus photographic lens is characterized in that spherical aberration is extremely large due to undercorrection or overcorrection. For this reason, in the present invention, an attachment lens that generates a large spherical aberration is mounted in front of a normal photographic lens (camera). However, the lens specifications are set such that the image plane does not change or the chromatic aberration fluctuates due to the mounting of the lens.

Since the attachment lens is detachably mounted on the front surface of a normal camera lens, the focal length of the attachment lens is generally infinite. However, when a negative spherical aberration is generated, an image is not removed. Since it is conceivable that the point moves somewhat negatively, the refractive power may be a slightly negative value.

Further, most of soft focus photographs are portraits or still life photographs, and most of them are photographed at a short distance. Therefore, in practice, the focal length of the attachment lens does not necessarily have to be infinite. For example, when used for portrait photography, when the attachment lens has a positive refractive power, it is considered that the focal length of the attachment lens should be about 800 mm or more.

The entrance pupil of a photographic lens is usually located inside or behind the lens. For this reason, it is required to suppress the fluctuation of the image plane by minimizing the refraction received when the light beam that reaches the image peripheral portion and forms an image passes through the attachment lens. In view of such demands, the soft focus attachment lens of the present invention is configured by combining two positive and negative lenses, and the centers of the radii of curvature of the surfaces of these lenses are all on the image field side or are in a planar shape. It is. That is, a meniscus lens having a convex surface facing the object side, a convex plano lens, or a plano-concave lens is used.

In the attachment lens of the present invention, a large spherical aberration is generated. In the case of generating a positive spherical aberration, the radius of curvature of the positive lens is made larger than the radius of curvature (bending) of the negative lens, and To generate spherical aberration, the radius of curvature of the negative lens is made larger than the radius of curvature of the positive lens. The magnitude of the spherical aberration generated at this time depends on the radius of curvature of each lens.

Further, a spherical aberration may be generated by giving a difference between the refractive indices of the positive and negative lenses. In the case of generating a negative spherical aberration, the refractive index of the negative lens is made larger than that of the positive lens. To generate a positive spherical aberration, the refractive index of the positive lens is made larger than that of the negative lens. However, in order to suppress the occurrence of chromatic aberration, the difference in the average dispersion of the materials of the positive and negative lenses is suppressed to within 30%, that is, the difference in the average dispersion is 3%.
Select a material that is within 0%.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific example of a soft focus attachment lens according to the present invention will be described with reference to the drawings. FIG.
12 to FIG. 12 show a plurality of embodiments, all of which are shown in FIG.
The soft focus attachment lenses 10 to 70 according to the embodiments of the present invention are detachably mounted on the front surface of the photographic lens 20 having the structure shown in FIG. 1 (that is, a camera having the photographic lens 20).

First, the photographic lens 20 will be described. As shown in FIG. 13, this photographic lens 20 is composed of four lenses L21 to L24 arranged in order from the object side on the optical axis 1, and the iris diaphragm 2 is arranged immediately behind the 23rd lens L23. Is established. The specifications of these lenses are set as shown in Table 1, and the focal length is 134.9.
Thus, the photographic lens has a maximum image height of 21.7 at F2.79.

[0017]

Table 1 Lens surface Curvature radius (r) Surface distance (d Refractive index Dispersion ratio L21 S1 59.436 7.2 1.6935 53.7 S2 780.64 0.1 L22 S3 56.991 21.0 1. 5168 64.1 S4 67.482 3.0 L23 S5-320.11 4.0 1.7552 27.6 S6 38.303 28.8 L24 S7 130.0 8.0 1.7170 50.2 S8 -118 .31

FIG. 14A shows the spherical aberration, FIG. 14B shows the astigmatism, and FIG. 14C shows the distortion in the photographic lens 20 having the above configuration. As can be seen from this graph, the aberration of the photographic lens 20 is suppressed to a small value, and a clear image can be obtained by using the photographic lens 20. In FIG. 14A,
The solid line indicates the d line, the dashed line indicates the C line, the one-dot chain line indicates the F line, and the two-dot chain line indicates the g line. In FIG. 14B, a solid line indicates the S image plane, and a dotted line indicates the M image plane. With respect to the aberration diagrams, the following embodiments are also given the same symbols.

FIG. 1 shows a state in which a soft focus attachment lens 10 according to a first embodiment of the present invention is mounted on the front surface of a photographic lens 20 having the above configuration. The attachment lens 10 includes a plano-concave negative lens L11 from the object side and a positive meniscus lens L having a convex surface facing the object side.
And 12. The lens specifications of these two lenses are set as shown in Table 2.

[0020]

Table 2 Lens surface Curvature radius (r) Surface spacing (d Refractive index Dispersion ratio L11 S1 0.0 2.0 1.7130 53.9 S2 100.0 0.1 L12 S3 60.0 6.5 1. 50137 56.4 S4 405.0

FIGS. 2A, 2B, and 2C show the spherical aberration, astigmatism, and distortion of the photographic lens 20 to which the attachment lens 100 is attached. As can be seen from this figure, this lens 10 produces a large negative spherical aberration. Therefore, if photographing is performed using the photographic lens 20 in which the lens 10 is mounted on the front as shown in FIG. 1, it is possible to obtain a good soft focus photograph with little change in the image plane and little chromatic aberration fluctuation.

FIG. 3 shows a state in which the soft focus attachment lens 30 according to the second embodiment is mounted on the front surface of the photographic lens 20 having the above configuration. This attachment lens 30 is a plano-concave negative lens L31 from the object side.
And a positive meniscus lens L32 having a convex surface facing the object side. The lens specifications of these two lenses are set as shown in Table 3.

[0023]

Table 3 Lens surface Curvature radius (r) Surface spacing (d Refractive index Dispersion ratio L31 S1 0.0 2.0 1.7130 53.9 S2 100.0 0.1 L32 S3 70.0 6.5 1. 50137 56.4 S4 13365.0

FIGS. 4 (a), 4 (b) and 4 (c) show the spherical aberration, astigmatism and distortion of the photographic lens 20 equipped with the attachment lens 30, and the lens 30 has a large negative spherical aberration. Generate. Therefore, a good soft focus photograph can be taken using the photographic lens 20 in which the lens 30 is mounted on the front as shown in FIG.

FIG. 5 shows a state in which the soft focus attachment lens 40 according to the third embodiment is mounted on the front surface of the photographic lens 20 having the above-described configuration. The attachment lens 40 is formed by bonding two positive meniscus lenses L41 and L42 with their convex surfaces facing the object side. The lens specifications of these two lenses are set as shown in Table 4.

[0026]

Table 4 Lens surface Curvature radius (r) Surface spacing (d Refractive index Dispersion ratio L41 S1 43.0 6.5 1.5013756.4 L42 S2 70.0 2.0 1.77279 49.5 S3 46. 958

FIGS. 6 (a), 6 (b) and 6 (c) show the spherical aberration, astigmatism and distortion of the photographic lens 20 equipped with the attachment lens 40. The lens 40 has a large negative spherical aberration. Generate. Therefore, a good soft focus photograph can be taken using the photographic lens 20 in which the lens 40 is mounted on the front as shown in FIG.

FIG. 7 shows a state in which the soft focus attachment lens 50 according to the fourth embodiment is mounted on the front surface of the photographic lens 20 having the above-described configuration. This attachment lens 50 is a plano-concave negative lens L51 from the object side.
And a positive meniscus lens L52 having a convex surface facing the object side. The lens specifications of these two lenses are set as shown in Table 5.

[0029]

Table 5 Lens surface Radius of curvature (r) Surface spacing (d Refractive index Dispersion ratio L51 S1 0.0 1.5 1.5168 64.1 S2 84.0 1.0 L52 S3 52.0 6.5 1. 5168 64.1 S4 132.94

FIGS. 8 (a), 8 (b) and 8 (c) show the spherical aberration, astigmatism and distortion of the photographic lens 20 equipped with the attachment lens 50. The lens 50 has a large negative spherical aberration. Generate. Therefore, good soft focus photography can be performed using the photographic lens 20 in which the lens 50 is mounted on the front as shown in FIG.

FIG. 9 shows a state in which the soft focus attachment lens 60 according to the fifth embodiment is mounted on the front surface of the photographic lens 20 having the above-described configuration. This attachment lens 60 is composed of two positive meniscus lenses L61 and L62 with the convex surface facing the object side. The lens specifications of both lenses are set as shown in Table 6.

[0032]

[Table 6] Lens surface Curvature radius (r) Surface spacing (d) Refractive index Dispersion ratio L61 S1 84.0 6.5 1.5168 64.1 S2 150.0 1.0 L62 S3 50.0 1.51 .5168 64.1 S4 38.578

FIGS. 10 (a), 10 (b) and 10 (c) show the spherical aberration, astigmatism and distortion of the photographic lens 20 equipped with the attachment lens 60. The lens 60 has a large positive spherical aberration. Generate. For this reason,
A good soft focus photograph can be taken by using the photographic lens 20 in which the lens 60 is mounted on the front as shown in FIG.

In each of the above embodiments, the focal length of the attachment lens is infinite, but FIG.
A sixth embodiment in which a 9 mm attachment lens 70 is mounted is shown. The attachment lens 70 includes two positive meniscus lenses L71 and L72 having convex surfaces facing the object side.
Consists of The lens specifications of both lenses are set as shown in Table 7.

[0035]

[Table 7] Lens surface Curvature radius (r) Surface distance (d) Refractive index Dispersion ratio L71 S1 40.0 7.5 1.5168 64.1 S2 140.0 1.5 L72 S3 233.0 2.01 .77279 49.5 S4 59.49313

FIGS. 12 (a), 12 (b) and 12 (c) show the spherical aberration, astigmatism and distortion of the photographic lens 20 equipped with the attachment lens 70. The lens 70 has a large positive spherical aberration. Generate. For this reason,
A good soft focus photograph can be taken using the photographic lens 20 having the lens 70 mounted on the front as shown in FIG.

In the above embodiment, the soft focus attachment lens is detachably mounted on the front surface of the photographic lens 20 shown in FIGS. 13 and 14, but the soft focus attachment lens according to the present invention is mounted. Of course, the photographic lens is not limited to this.

[0038]

As described above, according to the present invention,
A soft focus attachment lens made of two positive and negative lenses made of a material with a difference of 30% or less in average dispersion ratio is simply attached to the front of a normal camera (photo lens). Since a large spherical aberration is generated in the lens system as a whole, it is possible to take a soft focus photograph almost equivalent to the case where a dedicated soft focus photographic lens is used.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a lens configuration of a camera equipped with a soft focus attachment lens according to a first embodiment of the present invention.

FIG. 2 is a graph showing spherical aberration, astigmatism, and distortion in the lens system of FIG. 1;

FIG. 3 is an explanatory diagram showing a lens configuration of a camera equipped with a soft focus attachment lens according to a second embodiment of the present invention.

FIG. 4 is a graph showing spherical aberration, astigmatism, and distortion in the lens system of FIG. 3;

FIG. 5 is an explanatory diagram showing a lens configuration of a camera equipped with a soft focus attachment lens according to a third embodiment of the present invention.

FIG. 6 is a graph showing spherical aberration, astigmatism, and distortion in the lens system of FIG. 5;

FIG. 7 is an explanatory diagram showing a lens configuration of a camera equipped with a soft focus attachment lens according to a fourth embodiment of the present invention.

FIG. 8 is a graph showing spherical aberration, astigmatism, and distortion in the lens system of FIG. 7;

FIG. 9 is an explanatory diagram showing a lens configuration of a camera equipped with a soft focus attachment lens according to a fifth embodiment of the present invention.

FIG. 10 is a graph showing spherical aberration, astigmatism, and distortion in the lens system of FIG. 9;

FIG. 11 is an explanatory diagram showing a lens configuration of a camera equipped with a soft focus attachment lens according to a sixth embodiment of the present invention.

FIG. 12 is a graph showing spherical aberration, astigmatism, and distortion in the lens system of FIG. 11;

FIG. 13 is an explanatory diagram showing a lens configuration of a camera to which a soft focus attachment lens according to the present invention is attached.

14 is a diagram showing spherical aberration in the camera lens system shown in FIG. 13;
It is a graph which shows astigmatism and distortion.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Optical axis 2 Iris stop 10, 30, 40, 50, 60, 70 Soft focus attachment lens 20 Photo lens

Claims (5)

[Claims] 1. An attachment lens attached to the front side of an objective lens of a camera, comprising two positive and negative lenses made of a material having an average dispersion ratio difference of 30% or less. Has a shape in which the center of the radius of curvature is located on the image field side, and generates a large spherical aberration as a whole of the lens system of the camera in a state where the two positive and negative lenses are combined. Features a soft focus attachment lens. 2. The two positive and negative lenses are a positive meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a convex surface having a convex surface having a center of curvature on the image field side and a flat surface. 2. The method according to claim 1, wherein a positive and a negative lens are selected and combined one by one from a plano-concave lens and a plano-concave negative lens having a plane and a concave surface having a center of curvature on the image field side. The soft focus attachment lens according to 1. 3. The soft focus attachment lens according to claim 1, wherein the soft focus attachment lens has a positive refractive power in a state where the two lenses are combined, and has a focal length of 800 mm or more. 4. The soft focus attachment lens according to claim 1, wherein a focal length in a state where the two lenses are combined is substantially infinite. 5. The soft focus attachment lens according to claim 1, wherein the soft focus attachment lens has a negative spherical aberration and a weak negative refractive power when the two positive and negative lenses are combined. .