JPH0682691A - Anamorphic converter - Google Patents

Abstract

PURPOSE:To obtain the anamotphic converter which is mounted in front of a main photographing system and can optionally vary the aspect ratio of a photographic picture plane. CONSTITUTION:The anamorphic converter consists of three lenses, i.e., two 1st and 2nd meniscus lenses G1 and G2 in cylindrical shapes which have negative refracting power only horizontally on the basis of the photographic picture plane and are convex to an object side and a 3rd cylindrical lens G3 which has positive refracting power only horizontally and also has convex surfaces as both its surfaces in order from the object side, and satisfies 1.68<N1<N2 and 1.40<N3<(N1+N2)/2, where Ni is a refractive index of an (i)th lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anamorphic converter, and in particular, it is detachably attached to an object side of a main photographing system (master lens) and recorded with various aspect ratios of a photographing screen, and / or a recorded image. The present invention relates to an anamorphic converter suitable for a video camera, a television camera, a photographic camera, etc., in which various aspect ratios are projected.

[0002]

2. Description of the Related Art Conventionally, there is a converter which is detachably attached to the front (object side) or the rear (image side) of a main photographing system to change the aspect ratio (aspect ratio) of a photographing screen to record an image. Various proposals have been made.

In recent years, in the field of video cameras and television cameras, a recorded image with a normal aspect ratio of 3: 4 is widened by using a converter to have an aspect ratio of 9:16 and the recorded image is viewed. Such a system is used.

As a method of viewing an image with an aspect ratio of 9:16, as shown in FIG. 9, a camera with an aspect ratio of 3: 4 is used to partially cut (trim) the up and down direction of the image to display the aspect ratio. Record on the screen of 9:16. Then, there is an electric method for electrically enlarging the screen to obtain a reproduction screen having an aspect ratio of 9:16 when viewing.

In addition to this, as proposed in Japanese Patent Laid-Open No. 2-13916, an anamorphic converter is mounted in front of the main photographing system at the time of photographing to compress the image in the lateral direction to record an image, and to extend the lateral direction at the time of reproduction. Thus, there is an optical method for obtaining a horizontally long image by converting the aspect ratio of 3: 4 to the aspect ratio of 9:16 (see FIG. 10).

In the publication, an afocal converter made of a cylindrical lens is used as a conversion lens. Then, the curvature direction of the afocal converter is aligned with the horizontal direction of the screen and mounted in front of the camera, and the image is obtained by compressing the horizontal direction 0.75 times at the time of photographing. And when playing, the horizontal direction is 1.33
It has doubled. As a result, an image converted from the aspect ratio of 3: 4 to the aspect ratio of 9:16 is obtained.

[0007]

Aspect ratio 9:16
In the electrical method among the methods for obtaining the screen, the number of scanning lines is reduced by 25% at the stage of cutting the shooting screen in the vertical direction, for example, in the case of a television camera. Therefore, there is a problem that the vertical resolution of the image is deteriorated accordingly. Further, in the optical method, if the screen is compressed and expanded using a converter having high optical performance, the deterioration of the image is small.

However, in order to obtain a converter with high optical performance, if the lens configuration is not properly set, the number of lenses will become large and the focus driving force will increase, making rapid focus operation difficult.

According to the present invention, by properly setting the lens configuration, the main photographing system (master lens) has a simple configuration.
It is an object of the present invention to provide an anamorphic converter having high optical performance, which can be mounted on the object side of the device and can record and / or reproduce by arbitrarily changing the aspect ratio of the screen.

[0010]

The anamorphic converter of the present invention is an anamorphic converter that is mounted on the object side of a main photographing system and changes the aspect ratio of a photographing screen. Both the first and second meniscus-shaped first and second lenses, which have a cylindrical shape with convex surfaces facing the two object sides and have a negative refractive power only in the horizontal direction with respect to the screen, and a positive refractive power only in the horizontal direction. When the refractive index of the material of the i-th lens is N, it is composed of three lenses of a cylindrical third lens having a convex lens surface. 1.68 <N1 <N2 (1) 1.40 <N3 <(N1 + N2) / 2 ... (2) is satisfied.

[0011]

Embodiments FIGS. 1A and 1B are numerical embodiments 1 of the present invention.
FIG. 7 is a lens cross-sectional view when the anamorphic converter AC is mounted on the object side of a main imaging system (master lens) ML. In the figure, (A) is a horizontal section (horizontal section), and (B) is a vertical section (vertical section) with reference to the shooting screen F.
Is shown.

2 to 7 show aberration diagrams at the wide-angle end and the telephoto end when the anamorphic converters of Numerical Embodiments 1, 2, and 3 of the present invention are mounted in front of the main photographing system. In the aberration diagrams, (A) shows the horizontal direction and (B) shows the vertical direction.

Anamorphic converter A of this embodiment
C has two lens groups, a first lens unit L1 having a negative refractive power in the horizontal direction and a second lens unit L2 having a positive refractive power in the horizontal direction, and forms an image 0.75 times in the horizontal direction as a whole. It has an optical function as an afocal wide converter with magnification.

The first lens unit L1 is a meniscus-shaped first lens G1 having a cylindrical shape with a convex surface facing the object side, which has a negative refractive power only in the horizontal direction, and the first lens G1.
The second lens G2 has the same shape as the second lens G2.

The second lens unit L2 is composed of a third lens G3 having a cylindrical shape whose both lens surfaces have a positive refractive power only in the horizontal direction and are convex. Incidentally, G in the drawing is a glass block such as a face plate and a filter of the main photographing system ML. F is a shooting screen. Normally, an afocal wide converter is composed of two lens groups, a first group (front group) having a negative refractive power and a second group (rear group) having a positive refractive power.

In this embodiment, the first group having a strong negative refractive power is composed of two lenses having a predetermined shape, and the aberration correction is shared by each lens surface to reduce the amount of aberration generated. In particular, in the horizontal cross section, both the first lens and the second lens having negative refractive power have a meniscus shape with a convex surface facing the object side.

As a result, the incidence angle of the paraxial ray of the pupil on the lens surface becomes close to 90 degrees to reduce the occurrence of various aberrations, especially the distortion aberration. Also, the first lens and the second
The distance between the lens and the lens is shortened to reduce the overall size of the lens system. Then, the lens shapes of the first, second, and third lenses as well as the refractive indexes N1, N2, and N3 of the material are set so as to satisfy the conditional expressions (1) and (2), whereby various aberrations are corrected well. And has obtained high optical performance.

If the lower limit of conditional expression (1) is exceeded and the refractive index N1 of the material of the first lens becomes too low, the curvature of the cylindrical surfaces of the first lens and the second lens becomes strong in order to obtain a predetermined refractive power. However, as a result, astigmatism increases in the peripheral portion in the diagonal direction of the screen, which is not good.

Further, in order to reduce the chromatic aberration of magnification generated in the first lens group, it is better to lower the dispersion of the material of a lens having a higher incidence height of paraxial ray of the pupil. For this purpose, the Abbe number of the materials of the first lens and the second lens constituting the first group is ν1,
When ν2 is set, it is preferable to set ν1> ν2.

Generally, the refractive index of glass is 1.68.
In the larger region, the larger the refractive index, the larger the dispersion (the smaller Abbe number) of the glass.

Therefore, in this embodiment, the refractive index N1 is equal to the refractive index N.
Chromatic aberration is satisfactorily corrected by using glass in a region that is smaller than 2, that is, in a region that satisfies N1 <N2.

Conditional expression (2) is for reducing the Petzval sum of the entire system when the anamorphic converter of the present invention is mounted in front of the main photographing system.

In the reduction type converter of the two-group structure consisting of the first group having the negative refractive power and the second group having the positive refractive power, the negative refractive power of the first group is larger than that of the positive refractive power of the second group. Power becomes stronger.

Therefore, in this embodiment, in order to reduce the Petzval sum on the converter side, the average refractive index ((N1 + N2) / 2) of the materials of the first group is changed to the refractive index N of the materials of the second group.
It is larger than 3, that is, N3 <(N1 + N2) / 2.

If the lower limit of conditional expression (2) is exceeded and the refractive index N3 becomes too small, the curvature of the cylindrical surface of the second lens group becomes too strong, and astigmatism at the peripheral portion in the diagonal direction of the screen is generated. It is not good because it increases.

In the present invention, in order to obtain better optical performance over the entire screen, the radius of curvature in the horizontal direction of the lens surface of the third lens on the object side and the lens surface on the image side are respectively R3a,
When R3b, it is preferable to satisfy the condition of 0.3 <(R3b + R3a) / (R3b-R3a) <0.6.

If the curvature of the cylindrical surface on the object side becomes too loose or too strong beyond the upper limit or the lower limit of conditional expression (3), spherical aberration in the horizontal direction increases in either case. It's not good because it comes.

In the anamorphic converter of the present invention, the first lens and the second lens are moved to the image plane side and / or the third lens is moved to the object side to focus from an object at infinity to a close object. . Usually, when a converter of a magnification in the main photographing system is attached, the object distance is apparently the square of the magnification for the main photographing system.

Since the object distance changes only in the horizontal direction in the anamorphic converter of the present invention, when the anamorphic converter is mounted after focusing in the main photographing system, blurring occurs only in the horizontal direction as shown in FIG.

Therefore, in the present invention, as described above, the first group and the second group
Focusing is performed by changing the distance from the group.

Next, a numerical example 1 in the horizontal direction of the anamorphic converter of the present invention and a numerical example of the main photographing system will be shown. Note that the numerical values in the vertical direction of the anamorphic converter are all infinity, so they are omitted.

In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, and Di is the i-th lens surface from the object side.
The th lens thickness and the air gap, Ni and νi are the refractive index and the Abbe number of the glass of the ith lens in order from the object side.

The main photographing system shows the values from the lens surface R7, assuming that an anamorphic converter is mounted. When the aspherical shape is the X axis in the optical axis direction, the H axis in the direction perpendicular to the optical axis, the traveling direction of light is positive, and R is the paraxial curvature radii B, C, and D, each is an aspherical coefficient.

[0034]

[Equation 1] It is expressed by the formula.

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical example, and Table-2 shows the movement amount of the first group or the second group at each object distance in the numerical example 3. Shown in. Anamorphic Converter (Numerical Example 1) Synthesis f = 0.75 to 5.77 R 1 = 41.544 D 1 = 1.031 N 1 = 1.71300 ν 1 = 53.8 R 2 = 7.813 D 2 = 1.562 R 3 = 12.708 D 3 = 0.796 N 2 = 1.77250 ν 2 = 49.6 R 4 = 6.278 D 4 = 1.362 R 5 = 6.962 D 5 = 1.562 N 3 = 1.58313 ν 3 = 59.4 R 6 = -23.344 D 6 = 1.093 (Numerical Example 2) Synthesis f = 0.75 to 5.77 R 1 = 62.024 D 1 = 1.031 N 1 = 1.69680 ν 1 = 55.5 R 2 = 10.706 D 2 = 1.562 R 3 = 23.161 D 3 = 0.796 N 2 = 1.77250 ν 2 = 49.6 R 4 = 5.878 D 4 = 1.255 R 5 = 6.998 D 5 = 1.562 N 3 = 1.60311 ν 3 = 60.7 R 6 = -16.336 D 6 = 1.093 (Numerical Example 3) Synthesis f = 0.74 to 5.71 R 1 = 27.828 D 1 = 1.031 N 1 = 1.69680 ν 1 = 55.5 R 2 = 9.849 D 2 = 1.562 R 3 = 23.249 D 3 = 0.796 N 2 = 1.77250 ν 2 = 49.6 R 4 = 6.105 D 4 = 1.781 R 5 = 7.669 D 5 = 1.250 N 3 = 1.60311 ν 3 = 60.7 R 6 = -20.199 D 6 = 1.093 Main imaging system f = 1.00 to 7.69 FNO = 1: 1.85 to 2.57 2 ω = 53.1 ° to 7.4 ° R 7 = 4.345 D 7 = 0.156 N 4 = 1.80518 ν 4 = 25.4 R 8 = 2.489 D 8 = 0.843 N 5 = 1.58313 ν 5 = 59.4 R 9 = -12.927 D 9 = 0.031 R10 = 2.245 D10 = 0.304 N 6 = 1.69680 ν 6 = 55.5 R11 = 2.981 D11 = Variable R12 = 2.613 D12 = 0.078 N 7 = 1.88300 ν 7 = 40.8 R13 = 0.850 D13 = 0.468 R14 = -1.003 D14 = 0.078 N 8 = 1.51633 ν 8 = 64.2 R15 = 1.512 D15 = 0.281 N 9 = 1.84666 ν 9 = 23.8 R16 = 28.723 D16 = variable R17 = (aperture) D17 = 0.187 R18 = 2.006 D18 = 0.468 N10 = 1.60311 ν10 = 60.7 R19 = -7.246 D19 = Variable R20 = 2.460 D20 = 0.078 N11 = 1.84666 ν11 = 23.8 R21 = 1.067 D21 = 0.040 R22 = 1.224 D22 = 0.578 N12 = 1.58313 ν12 = 59.4 R23 = -2.335 D23 = 0.734 R24 = ∞ D24 = 0.828 N13 = 1.51633 ν13 = 64.2 R25 = ∞ Aspheric surface R18; B = -8.23 × 10 ^-8 , C = -8.19 × 10 ^-12 , D = -2.94 × 10 ^-15 R23; B =- 4.48 × 10 ^-8 , C = -6.65 × 10 ^-12 , D = -9.95 × 10 ^-14

[0036]

[Table 1]

[0037]

As described above, according to the present invention, by properly setting the lens configuration as described above, the lens is mounted on the object side of the main photographing system (master lens) with a simple configuration to increase the aspect ratio of the screen. It is possible to achieve an anamorphic converter having high optical performance that can be arbitrarily recorded and / or reproduced.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view when an anamorphic converter according to Numerical Embodiment 1 of the present invention is mounted in front of a main photographing system.

FIG. 2 is an aberration diagram in the horizontal and vertical directions at the wide-angle end when the anamorphic converter of Numerical Embodiment 1 of the present invention is attached to the main imaging system.

FIG. 3 is an aberration diagram in the horizontal and vertical directions at the telephoto end when the anamorphic converter of Numerical Embodiment 1 of the present invention is attached to the main imaging system.

FIG. 4 is an aberration diagram in the horizontal and vertical directions at the wide-angle end when the anamorphic converter according to Numerical Example 2 of the present invention is attached to the main imaging system.

FIG. 5 is an aberration diagram in the horizontal and vertical directions at the telephoto end when the anamorphic converter of Numerical Example 2 of the present invention is attached to the main imaging system.

FIG. 6 is an aberration diagram in the horizontal and vertical directions at the wide-angle end when the anamorphic converter according to Numerical Example 3 of the present invention is attached to the main imaging system.

FIG. 7 is an aberration diagram in the horizontal and vertical directions at the telephoto end when the anamorphic converter of Numerical Example 3 of the present invention is attached to the main imaging system.

FIG. 8 is an aberration diagram at the wide-angle end and the telephoto end of the main imaging system.

FIG. 9 is an explanatory diagram of an aspect ratio of a shooting screen

FIG. 10 is an explanatory diagram of an aspect ratio of a shooting screen.

FIG. 11 is an explanatory diagram of a focus state when an anamorphic converter is attached.

[Explanation of symbols]

 AC anamorphic converter L1 1st group L2 2nd group G Glass block ML Main imaging system d d line g g line ΔS Sagittal image plane ΔM Meridional image plane F Image plane (longitudinal and horizontal screens)

Claims (3)

[Claims] 1. An anamorphic converter which is mounted on the object side of a main photographing system and changes the aspect ratio of a photographing screen, wherein the anamorphic converter has negative refraction only in the horizontal direction in order from the object side with respect to the photographing screen. Cylindrical shape with the convex surface facing the two objects that have power,
And a meniscus-shaped first lens and a second lens, and three lenses, a cylindrical third lens having convex surfaces on both lens surfaces having positive refractive power only in the horizontal direction, and a refractive index of a material of the i-th lens. An anamorphic converter that satisfies the following condition: 1.68 <N1 <N2 1.40 <N3 <(N1 + N2) / 2. 2. When the radius of curvature in the horizontal direction of the object-side and image-side lens surfaces of the third lens is R3a and R3b, respectively 0.3 <(R3b + R3a) / (R3b-R3a) <0.6 The anamorphic converter according to claim 1, which satisfies the following condition. 3. The first lens and the second lens are moved to the image plane side and / or the third lens is moved to the object side to focus from an object at infinity to a close object. The anamorphic converter according to claim 1 or 2.