JP2511824B2 - Chromatic aberration correction lens and photographing system using the same - Google Patents

Description

The present invention relates to a chromatic aberration correction lens and an image pickup system using the same, and more particularly to a prism made of a material having a predetermined thickness, for example, a three-color separation prism, on the image plane side. The image of the taking lens for correcting the variation of chromatic aberration that occurs when taking a picture by placing a prism made of a material having a thickness different from the designed value in the taking lens for a television camera designed to be arranged and used. The present invention relates to a chromatic aberration correction lens for arranging on the surface side and a photographing system using the same.

(Prior Art) Conventionally, a color television camera is provided with an image pickup device for three primary colors, and light from a photographing lens is transmitted through a color separation prism to a three-color image sensor.
The primary colors are separated and guided onto each image sensor. The taking lens used in the color television camera is designed so that various aberrations are favorably corrected only when a color separation prism made of a material having a predetermined thickness is arranged on the image side.

Therefore, for example, when a color separation prism made of a material having a thickness different from the designed value is used, a large amount of chromatic aberration occurs, which causes deterioration of image quality.

For example, for a BK7 (nd = 1.51633, νd = 64.1) material with a 65 mm-thick color separation prism, an aberration-corrected shooting lens (hereinafter referred to as "BK7 correction lens") has a material of F5 (n
When a color separation prism (hereinafter referred to as "F5 prism") consisting of a prism with a thickness of 30 mm and a prism with a material of BK7 and a thickness of 20 mm (d = 1.60342, νd = 38.0) is installed, the difference in material and the prism Due to the disagreement of the lengths, a large amount of axial chromatic aberration, particularly spherical aberration, occurs.

Spherical aberration can be relatively easily corrected by inserting parallel plane glass and adjusting the prism length as disclosed in Japanese Utility Model Laid-Open No. 57-71313.

However, it is difficult to correct the axial chromatic aberration simply by inserting the plane-parallel glass. When the BK7 correction lens is attached to the F5 prism via the 15 mm thick parallel plane BK7 glass, the blue image is displaced from the lens in the direction away from the green image, and the red image is compared to the green image. And is displaced to the lens side to form an image. As represented by the Franhofer line, the g line (436 nm) is displaced by 107 μ with respect to the d line (588 nm), and the c line (656 nm) is displaced by −22 μ with respect to the d line.

A taking lens for a television camera is designed in a state close to a so-called telecentric state so that an exit pupil is at infinity in order to prevent color shading caused by displacement of an incident angle of a color separation prism on a dichroic film. Therefore, even if the material of the prism is different from the designed material, the axial chromatic aberration changes but the lateral chromatic aberration does not change at all.

When an image pickup tube is used as the image pickup means, the image pickup tube can be moved back and forth. Therefore, even if some axial chromatic aberration remains in the taking lens, the position of the image pickup tube should be adjusted to the image forming position of each color. .

However, in recent years, the number of color television cameras in which a solid-state image sensor is fixedly used on a prism exit surface has been increasing.
In this case, since the position of the image pickup device cannot be adjusted, if a taking lens having a different prism correction is attached, the axial chromatic aberration is destroyed, and so-called tracking deviation occurs.

Axial chromatic aberration can be corrected by using a lens composed of a doublet lens in which two parallel plane glasses having the same refractive index nd and having different dispersions with matched prism lengths are pasted together.

However, this method has a problem that so-called registration error occurs because the chromatic aberration of magnification changes simultaneously with the correction of the axial chromatic aberration.

(Problems to be Solved by the Invention) The present invention provides a photographing lens designed for a prism of a predetermined material and thickness, for example, a color separation prism for separating three primary colors, and a material different from the design value and having a thickness. The axial chromatic aberration and the magnification aberration that occur when photographing is performed using different prisms can be corrected in good balance. In particular, it is an object of the present invention to provide a taking lens for a color television camera and a chromatic aberration correcting lens suitable for a taking system using the taking lens.

(Means for Solving Problems) (1-1) A chromatic aberration correction lens according to the present invention is provided with (1-1) a prism having a predetermined thickness disposed on the image surface side, which is disposed on the image surface side of a photographing lens to be used. In a chromatic aberration correction lens for correcting chromatic aberration of a system, when the three lenses made of at least two kinds of materials are bonded so that all bonding surfaces are concave toward the image side, When the Abbe numbers of the materials of the three lenses are νa, νb, νc in order from the object side and the radii of curvature of the cemented lens surfaces are Rb, Rc in order from the object side, νa> νb νb <νc | Rb | ≧ | Rc | It is characterized by satisfying the condition.

In particular, at least two lenses among the three lenses have different refractive indexes, and the first lens surface and / or the final lens surface on the object side has a curvature.

(1-2) In a chromatic aberration correction lens in which a prism having a predetermined thickness is arranged on the image surface side and arranged on the image surface side of a photographing lens to be used to correct chromatic aberration of the entire system, at least 2 of the chromatic aberration correction lens is provided. When three lenses made of different materials are laminated so that the cemented surfaces are all concave toward the image side, the Abbe numbers of the materials of the three lenses are νa, νb, νc in order from the object side. , Rb and Rc are the radii of curvature of the cemented lens surfaces in order from the object side, the condition of νa <νb νb> νc | Rb | ≧ | Rc | is satisfied.

In particular, at least two lenses among the three lenses have different refractive indexes, and the first lens surface and / or the final lens surface on the object side has a curvature.

An imaging system using the chromatic aberration correction lens of the present invention is (2-1) smaller than the Abbe number of the material of the prism in an imaging device in which a prism having a predetermined thickness is arranged on the image plane side of the imaging lens. When another prism made of a material of Abbe number is used, a chromatic aberration correction lens for correcting the chromatic aberration of the entire system is arranged on the image plane side of the taking lens, and the chromatic aberration correction lens is composed of at least two types of materials. Are laminated so that all the cemented surfaces are concave toward the image side, and the Abbe numbers of the materials of the three lenses are νa, νb, νc in order from the object side, and the curvature of the cemented lens surface. It is characterized in that when the radii are Rb and Rc from the object side, the condition of νa> νb νb <νc | Rb | ≧ | Rc | is satisfied.

In particular, at least two lenses among the three lenses have different refractive indexes, and the first lens surface and / or the final lens surface on the object side has a curvature.

(2-2) In an image pickup apparatus in which a prism having a predetermined thickness is arranged on the image plane side of a photographing lens and used, when using another prism made of a material having an Abbe number larger than the Abbe number of the material of the prism, A chromatic aberration correction lens that corrects the chromatic aberration of the entire system is arranged on the image side of the taking lens, and three lenses made of at least two kinds of materials are attached to the chromatic aberration correction lens. When the three lenses are bonded so as to face each other, and the Abbe numbers of the materials of the three lenses are νa, νb, νc in order from the object side, and the radii of curvature of the cemented lens surfaces are Rb, Rc in order from the object side, νa <Νb νb> νc | Rb | ≧ | Rc | is characterized by satisfying the condition.

In particular, at least two lenses among the three lenses have different refractive indexes, and the first lens surface and / or the final lens surface on the object side has a curvature.

(Example) FIG. 1 is a schematic view of an optical system of an example when the present invention is applied to a photographing system for a television camera.

In the figure, reference numeral 1 denotes a taking lens, which is composed of a substantially telecentric optical system such as a lens having a single focal length and a zoom lens. 2 is a chromatic aberration correction lens according to the present invention,
Reference numeral 3 is a color separation prism for separating the three primary colors.

The chromatic aberration correction lens 2 is composed of a cemented lens in which three lenses La, Lb, and Lc are bonded together. Of these, the lens La
And the lens Lc are made of the same material, that is, the Abbe numbers νa and ν
c is the same, and the refractive indices na and nc are also the same. Further, although the refractive index nb of the material of the lens Lb is substantially equal to the refractive index of the material of the lenses La and Lc, the Abbe number νb is the Abbe number νa, ν of the lenses La and Lc.
It is made of a material smaller than c. The relationship between the Abbe number and the refractive index of the materials of these three lenses is na ≈ nb ≈ nc νa ≈ νc> νb.

Further, the first lens surface Ra and the final lens surface Rc 'of the chromatic aberration correction lens 2 are flat in this embodiment for simplicity, and the cemented lens surfaces Rb and Rc have substantially the same curvature, and these cemented lens surfaces are Both are configured so that the concave surface faces the image side.

Regarding the d-line, the chromatic aberration correction lens in this embodiment acts as a plane-parallel glass because the three lenses La, Lb, and Lc have substantially the same refractive index, and thus acts as a correction for spherical aberration.

On the other hand, the bonded lens surface Rb acts as a positive refracting power for the g-line having a shorter wavelength than the d-line,
Rc acts as a negative refractive power. The off-axis chief ray travels substantially parallel to the optical axis because the taking lens is configured to be substantially telecentric. Therefore, the incident heights on the cemented lens surfaces Rb and Rc are substantially equal. As a result, the effects of the negative and positive refracting powers are canceled out, so that the lateral chromatic aberration is not affected.

On the other hand, the on-axis rays that focus on the optical axis are the surfaces of the cemented lens.
If the incident heights on Rb and Rc are Hb and Hc respectively, then Hb> Hc.
The axial chromatic aberration is represented by h ² · φ / ν, where h is the height of incidence on the lens surface, φ is the refractive power, and ν is the Abbe number, and is proportional to the square of the incident height h. For this reason, the cemented lens surface Rb has a large effect and positive refractive power acts as a whole, so that the g-line is imaged in the direction approaching the lens, and the image displacement due to the F5 prism can be canceled.

In the present embodiment, when the incident heights Hb 'and Hc' of the off-axis chief ray on the cemented lens surfaces Rb and Rc differ due to the lens thickness of the lens Lb, for example, Hb '<Hc In the case of ', the chromatic aberration of magnification changes slightly. In this case, if the radii of curvature Rb and Rc of the cemented lens surface are set as | Rb |> | Rc |, it is possible to excellently correct the change in lateral chromatic aberration.

As described above, in this embodiment, the front cemented lens surface Rb is insufficiently achromatized, and the rear cemented lens surface Rc is configured to be achromatized excessively, and the incident heights of the axial ray and the off-axis chief ray are increased. By utilizing the difference between the two, both lateral chromatic aberration and axial chromatic aberration are corrected in a well-balanced manner.

Further, by setting each lens shape such that all the cemented lens surfaces are concave toward the image plane side, the chromatic aberration is effectively corrected and the chromatic difference of the spherical aberration is satisfactorily corrected. For example, if the central lens Lb is a biconvex lens, in order to obtain the above-mentioned effect, the Abbe number ν of the material of the lens 3
Since a, νb, νc must be set to νa>νb> νc, and the selection range of glass is limited, it is sufficient if there are many types of glass. If not, the lens Lb is set as in this embodiment. It is better to have a meniscus shape.

In the present embodiment, the case where the refractive indexes na, nb and nc of the materials of the three lenses are na≈nb≈nc is shown for the sake of simplicity, but the refractive indexes of the materials of the three lenses are not necessarily equal. , All may be made of different materials.

For example, if the refractive index nb of the material of the central lens Lb is
It may be configured to have a higher refractive index than the materials of La and Lc. By doing so, it becomes easy to increase the ratio of Abbe number νb and νa or νb and νc to about 2, and it is possible to satisfactorily correct chromatic aberration. If a difference in refractive index occurs, spherical aberration will occur on the surface of the cemented lens, but if the spherical aberration at this time is large and the image quality deteriorates, the refractive index of the material of the lenses La and Lc is na ≈ If it is set to nc, it is possible to cancel out the spherical aberration generated at the front cemented lens surface Rb and the rear cemented lens surface Rc.

In the present embodiment, the first lens surface Ra of the chromatic aberration correction lens
Alternatively, a weak refracting power may be given to at least one lens surface of the final lens Rc 'to correct various aberrations generated from the cemented lens or to control the entire refracting power of the chromatic aberration correcting lens.

Also, when a prism with a large Abbe number is attached to a taking lens whose prism is corrected with a material with a small Abbe number, it is necessary to reverse the magnitude relationship between the materials of the three lenses that make up the chromatic aberration correction lens. The invention can be similarly applied.

That is, when the Abbe numbers of the materials of the three lenses are νa, νb, and νc from the object side, νa <νb νb> νc.

Next, numerical examples of the present invention will be shown. In the numerical example
Ri is the radius of curvature of the i-th lens surface in order from the object side, Di
Is the i-th lens thickness and air gap from the object side, Ni and ν
i is the refractive index and Abbe number of the glass of the i-th lens in order from the object side.

R1 to R33 in Numerical Embodiment 1 are zoom lenses designed by disposing a BK-7, 65 mm thick prism on the image plane side. R34 to R37 are chromatic aberration correction lenses according to the present invention, R38 to R
40 is equivalent to the F5 prism. 2 and 3 are a lens cross-sectional view and aberration diagrams at the wide-angle end in Numerical Example 1. F5 rhythm (R34 to R37) in Numerical Example 1
FIG. 4 shows an aberration diagram when a BK-7, 65 mm-thick prism, which is the original design object, is used instead of the above.

Next, numerical example 2 of the chromatic aberration correction lenses (R34 to R37) and the F5 prism arranged on the image side of the zoom lens shown in numerical example 1 will be shown.

In this embodiment, the Abbe number ratio νa / νb of the cemented lens,
νc / νb is set to a large value of 2.46, and the refractive index difference is set to a relatively large value, so that the chromatic aberration is satisfactorily corrected as a whole. FIG. 5 shows aberration diagrams at the wide-angle end in Numerical Example 2.

(Effects of the Invention) According to the present invention, if a chromatic aberration correction lens having a configuration in which three lenses having a predetermined shape and having a predetermined optical characteristic are attached to each other as described above is attached to the image plane side of the photographic lens, the photographic lens High optical performance with well-balanced correction of axial chromatic aberration, lateral chromatic aberration, spherical aberration, and other aberrations even when a prism with a different thickness from the design value is placed on the image surface side of the It is possible to achieve an imaging system that can be easily obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an optical system of an embodiment when the present invention is applied to a photographing system for a television camera, and FIGS. 2 and 3 are numerical embodiments 1 when the present invention is applied to a zoom lens. 4 is an aberration diagram when the original prism is attached to the zoom lens of Numerical Example 1, and FIG. 5 is a Numerical Example 2 when the present invention is applied to the zoom lens. It is an aberration diagram. In the figure, 1 is a taking lens, 2 is a chromatic aberration correction lens, 3 is a color separation prism, g is g line, c is c line, and Δ is in the aberration diagram.
S is the sagittal image plane, ΔM is the meridional image plane, and Y is the image height.

Claims (8)

(57) [Claims] 1. A chromatic aberration correction lens for arranging a prism having a predetermined thickness on the image surface side and arranging the prism on the image surface side of a photographing lens to be used to correct chromatic aberration of the entire system. When three lenses made of different materials are laminated so that the cemented surfaces are all concave toward the image side, the Abbe numbers of the materials of the three lenses are νa, νb, νc in order from the object side. A chromatic aberration correcting lens, wherein the radii of curvature of the cemented lens surfaces are Rb and Rc in order from the object side, then νa> νb νb <νc | Rb | ≧ | Rc | 2. At least two lenses among the three lenses have different refractive indexes, and the first lens surface and / or the final lens surface on the object side have a curvature. The chromatic aberration correction lens according to claim 1. 3. A chromatic aberration correction lens for arranging a prism having a predetermined thickness on the image surface side and arranging the prism on the image surface side of a photographing lens to be used to correct the chromatic aberration of the entire system. When three lenses made of different materials are laminated so that the cemented surfaces are all concave toward the image side, the Abbe numbers of the materials of the three lenses are νa, νb, νc in order from the object side. A chromatic aberration correction lens, characterized in that when the radii of curvature of the cemented lens surfaces are Rb and Rc in order from the object side, νa <νb νb> νc | Rb | ≧ | Rc |. 4. The refractive index of at least two lenses of the three lenses is different, and the first lens surface and / or the final lens surface on the object side has a curvature. The chromatic aberration correction lens according to claim 3. 5. An image pickup apparatus in which a prism having a predetermined thickness is arranged on the image plane side of a photographing lens and used, when another prism made of a material having an Abbe number smaller than that of the prism is used, A chromatic aberration correction lens that corrects the chromatic aberration of the entire system is arranged on the image side of the taking lens, and three lenses made of at least two kinds of materials are attached to the chromatic aberration correction lens. When the three lenses are bonded so as to face each other, and the Abbe numbers of the materials of the three lenses are νa, νb, νc in order from the object side, and the radii of curvature of the cemented lens surfaces are Rb, Rc in order from the object side, νa An imaging system characterized by satisfying a condition of> νb νb <νc | Rb | ≧ | Rc |. 6. The refractive index of at least two lenses of the three lenses is different, and the first lens surface and / or the final lens surface on the object side has a curvature. The imaging system according to claim 5. 7. An image pickup device in which a prism having a predetermined thickness is arranged on the image plane side of a photographing lens and is used, when another prism made of a material having an Abbe number larger than that of the prism is used, A chromatic aberration correction lens that corrects the chromatic aberration of the entire system is arranged on the image side of the taking lens, and three lenses made of at least two kinds of materials are attached to the chromatic aberration correction lens. When the three lenses are bonded so as to face each other, and the Abbe numbers of the materials of the three lenses are νa, νb, νc in order from the object side, and the radii of curvature of the cemented lens surfaces are Rb, Rc in order from the object side, νa <Νb νb> νc | Rb | ≧ | Rc |, which satisfies the condition. 8. The refractive index of the material of at least two of the three lenses is different, and the first lens surface and / or the final lens surface on the object side has a curvature. The imaging system according to claim 7.