JP2706789B2 - Large aperture ratio lens for close-up photography - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention has a large aperture ratio, an extremely long back focus and an exit pupil, and a shooting magnification of 1 / infinity from an infinite object distance.
The present invention relates to a large-aperture-ratio lens capable of performing close-up photography with aberration correction favorably performed up to twice.

(Prior art) A news TV lens called an ENG TV lens has a very long back focus because a three-color separation prism is inserted into the lens back, and a long exit pupil to prevent color shading. When used in a CCD three-plate camera, various design conditions are required, such as a small chromatic aberration of magnification.

Heretofore, there has been no so-called large aperture ratio macro lens that can perform short-range shooting from infinity at an object distance to a photographic magnification of 1/2, despite being an ENG TV lens satisfying all of these conditions.

(Object of the Invention) It is an object of the present invention that the back focus has a focal length of about 80.
Providing a large aperture ratio lens that can be used as a macro lens for ENG, with aberrations corrected from infinity at an object distance of approx. Is to do.

(Constitution of the Invention) The present invention provides, in order from the light incident side, an I-th lens unit having a positive refractive power, an aperture, a second lens unit having a positive refractive power, and a third lens unit having a positive refractive power. When focusing from infinity to a short distance from the object distance, the first and second lens units and the aperture are extended integrally, and the first lens unit has a concave surface facing the first unit and the image side of the positive lens. The second lens group is composed of a negative lens having a concave surface facing the object side and a positive lens having a convex surface facing the image side. The third lens group is composed of a sixth group, which is a compound lens of at least one concave lens and one convex lens, f: Focal length of the entire system f: Composite focal length of the I-th lens group If: Composite focal length of the II-th lens group II D ₃ : Combination of the third group in the II-th lens group, a cemented lens of a concave lens and a convex lens Thickness Ds ₃ : Distance from the stop to the _third group in the second lens group ν ₁ : Satisfies each condition of the first group, and has a long back focus and a long exit pupil. It is a large aperture ratio lens.

The present invention also includes an I-th lens group having a positive refractive power in order from the light incident side, an aperture, a second lens group having a positive refractive power, and a third lens group having a positive refractive power,
When focusing from infinity to a short distance from the object distance, the first and second lens units and the diaphragm are extended as one unit. The first lens unit includes a first lens unit of the positive lens and a positive lens having a convex surface facing the object side. The second lens group is a cemented lens of a negative lens having a concave surface facing the object side and a positive lens having a convex surface facing the image side. The third group and the fourth of each positive lens
The third lens group includes at least one group.
The sixth lens, which is a compound lens of one concave lens and one convex lens
Composed of groups, f: Focal length of the entire system f: Composite focal length of the I-th lens group If: Composite focal length of the II-th lens group II D ₃ : Combination of the third group in the II-th lens group, a cemented lens of a concave lens and a convex lens Thickness Ds ₃ : Distance from the stop to the _third group in the second lens group ν ₁ : Satisfies each condition of the first group, and has a long back focus and a long exit pupil. It is a large aperture ratio lens.

In general, a Gaussian lens is a lens type that has a relatively large aberration and a small variation in aberration due to a change in photographing distance. This is mainly because out-of-axis coma aberration is generated in off-axis light.If it is desired to maintain the aberration well up to a photographic magnification of 1/2, it is necessary to provide a floating mechanism to reduce this coma aberration. It needs to be corrected. In the present invention, when focusing from infinity to a short distance object point,
This problem was solved by moving out the I and II lens units and the diaphragm as one unit while keeping the III group fixed.

In order to reduce the aberration variation due to the shooting distance, it is desirable to use a lens configuration that is symmetrical with respect to the aperture and that is capable of minimizing the aberration generated by each lens, and the Gaussian type satisfies this requirement. . But ENG
In order to obtain a sufficiently long back focus necessary for a TV lens for use, the refractive power of the first lens group before the stop tends to be significantly weaker than the refractive power of the second lens group after the stop.

In the case of an optical system for short-distance photographing up to a photographing magnification of 1/2, if the refractive power of the I-th lens unit is too weak, the light flux coming out of the object is not converged very much by the I-th lens unit and becomes infinite. What is a convergent light beam for a distant object point becomes a divergent light beam for a near object point. If the divergence is too strong, the burden of aberration correction in the second lens group increases.
Spherical aberration and astigmatism become larger as the distance from infinity to short-distance shooting increases.However, the fluctuation of these aberrations increases, and a configuration that can favorably correct aberrations from infinity to a photographic magnification of 1/2 times. It becomes difficult to do.

Therefore, for an object point at infinity, the light beam emerging from the first lens unit is a weak convergent light beam, and for a short-distance object point with a photographic magnification of 1/2, it is a weak divergent light beam. It is desirable to configure.

Wherein the condition (i), when f ₁ exceeds the upper limit, the II
The load of aberration correction of the lens group increases, and it becomes difficult to suppress the fluctuation of aberration due to the change of the photographing distance. If the lower limit is exceeded, it becomes difficult to increase the back focus.

According to the present invention, in order to enable short-distance shooting up to a magnification of 1/2, as described above, when focusing on a short-distance object point, the second
A floating mechanism is used in which the I-th lens group, the II-th lens group, and the aperture are unified while the I-lens group is fixed.

In order to reduce the amount of extension of the first and second lens units and the aperture that are extended for focusing on a short-distance object point, the first,
It is necessary to keep the combined focal length of the second lens group as short as possible. This means that the third lens group, namely the sixth
The combined focal length of the group becomes very long, which increases the dead space and shortens the back focus.

Also, since the purpose is to obtain a large aperture ratio,
The lens thickness of the II / III lens group is increased or the number of lenses is increased, which also causes the back focus to be shortened.

Therefore, the condition (i) alone is not sufficient to obtain a long back focus required as a TV lens for ENG. To compensate for this, if the concave surface on the object side of the third lens unit is strengthened, the back focus can be lengthened.
The combined power of the II lens group is positive, and by increasing the power of the fourth and fifth groups, off-axis coma aberration increases and spherical aberration increases. As a result, the combined thickness of the concave lens and the convex lens of the third group in the second lens group is increased, and the luminous flux is rejected.

In the condition (ii), when D ₃ exceeds the upper limit, in this lens configuration, variation in lateral chromatic aberration due to focusing distance change becomes too large. If the lower limit is exceeded, it becomes difficult to make the back focus sufficiently long. The exit pupil position is
The distance D _S3 of the II lens group from the diaphragm is substantially determined by the relationship of the II lens group combined focal length f _II.

In order to lengthen the exit pupil, it is necessary to lengthen _DS3 or shorten the composite focal length of the second lens group. The luminous flux exiting the I-th lens group is a weak convergent luminous flux at an infinite object distance. Therefore, if the distance D _S3 from the stop to the second lens group is increased to maintain the back focus, the combined focal length of the I-th lens group is reduced. In other words, the composite focal length of the second lens group is shortened.

In the above condition (iii), if f _II / _{DS 3} exceeds the upper limit, the exit pupil does not extend. If the lower limit is exceeded, fluctuations of spherical aberration, astigmatism, and chromatic aberration of magnification due to a change in shooting distance cannot be suppressed to a small extent. To be usable for CCD3 board camera,
It is necessary to keep the chromatic aberration of magnification sufficiently small. In order to reduce the variation of the chromatic aberration of magnification due to the change in the photographing distance, it is necessary to reduce the amount of change in the chromatic aberration of magnification of the I-th lens unit and the II-th lens unit which is extended at a short distance. In particular, since the second lens group has a strong refractive power, the fluctuation of the chromatic aberration of magnification must be kept small, but the axial chromatic aberration changes to a relatively large under value as the object distance from infinity to short distance. Therefore, the I-th lens unit must change the axial chromatic aberration relatively large and excessively so as to cancel the object distance infinity from infinity to a short distance, and also suppress the change amount of the chromatic aberration of magnification to be small. No.

As described above, the condition (iv) is a condition for minimizing the amount of change of the axial chromatic aberration caused by the change in the photographing distance generated in the second lens group, and for maintaining the axial and lateral chromatic aberrations as a whole as good as possible. .

(Example) Next, data of a numerical example of the present invention will be shown. here,
f, FNo., 2ω, BF, Exp. represent the focal length, aperture ratio, angle of view, back focus, and exit pupil position from the imaging plane of the entire system when focusing on an object at infinity, and Ri is The radius of curvature of the i-th lens surface from the object side, di is the i-th lens thickness and air spacing in order from the object side, and Ni and νi are the d-line refractive index and d of the i-th glass from the object side, respectively. Represents the Atsube number for the line.

In addition, the lens back insertion glass is 33.5 mm thick and the glass material is Nd
= 1.55920, νd = 53.90 parallel plane glass and thickness 10.75mm
Is a parallel-plane glass with Nd = 1.51633 and vd = 64.15.

[Example 1] f = 1.0 FNo. = 1.4 2ω = 12.4 ゜ BF = 0.778 Exp. = − 14.844 R ₁ = 0.7436 d ₁ = 0.121 N ₁ = 1.72342 ν ₁ = 37.95 R ₂ = 6.2374 d ₂ = 0.020 R ₃ = 0.6455 d ₃ = 0.119 N ₂ = 1.74320 ν ₂ = 49.31 R ₄ = 0.3643 d ₄ = 0.178 R ₅ = ∞ d ₅ d ₅ = 0.178 R ₆ = -0.3607 d ₆ = 0.15818 N ₃ = 1.80518 ν ₃ = 25.43 R _{7 = 2.6753 d 7 = 0.178 N} 4 = 1.58913 ν 4 = 61.18 R 8 = -0.5937 d 8 = 0.004 R 9 = -22.2512 d 9 = 0.113 N 5 = 1.80610 ν 5 = 40.95 R 10 = -0.7998 d 10 = 0.004 R ₁₁ = 1.4870 d ₁₁ = 0.079 N ₆ = 1.64000 v ₆ = 60.09 R ₁₂ = -14.9842 d ₁₂ = ^* Variable R ₁₃ = -1.0237 d ₁₃ = 0.020 N ₇ = 1.64769 v ₇ = 33.80 R ₁₄ = 0.7449 d ₁₄ = 0.079 R ₁₅ = 1.0665 d ₁₅ = 0.125 N ₈ = 1.72342 ν ₈ = 37.95 R ₁₆ = -0.8947 When the object distance d ₀ = d, d ₁₂ = 0.089 When the object distance d ₀ = 1.769, that is, when the photographing magnification β = -0.5 D ₁₂ = 0.572 [Example 2] f = 1.0 FNo. = 1.4 2ω = 12.6 ゜ BF = 0.8 _{. 03 Exp = - 5.805 R 1} = 1.5082 d 1 = 0.122 N 1 = 1.75520 ν 1 = 27.51 R 2 = -13.6927 d 2 = 0.08 R 3 = 0.7524 d 3 = 0.09 N 2 = 1.71300 ν 2 = 53.84 R 4 = _{1.4000 d 4 = 0.026 N 3 =} 1.64769 ν 3 = 33.80 R 5 = 0.4833 d 5 = 0.2 R 6 = ∞ d 6 = 0.2 R 7 = -0.4351 d 7 = 0.2 N 4 = 1.80518 ν 4 = 25.43 R 8 = 15.4036 _{d 8 = 0.24 N 5 = 1.77250} ν 5 = 49.60 R 9 = -0.7086 d 9 = 0.004 R 10 = -13.8990 d 10 = 0.084 N 6 = 1.77250 ν 6 = 49.60 R 11 = -1.4750 d 11 = 0.004 R 12 = _{1.8215 d 12 = 0.072 N 7 =} 1.62041 ν 7 = 60.28 R 13 = -6.6155 d 13 = * variable _{R 14 = -2.2419 d 14 = 0.02} N 8 = 1.51742 ν 8 = 52.41 R 15 = 0.8668 d 15 = 0.02 R 16 = 1.1309 when _{d 16 = 0.12 N 9 = 1.69680} ν 9 = 55.53 R 17 = -1.8727 BF object distance d ₀ = ∞, when d ₁₃ = 0.072 object distance d ₀ = ie imaging magnification beta = -0.5 when 1.811 d ₁₃ = 0.708 example 3 f = 1.0 FNo = 1.4 2ω = 12.6 ° BF = 0.799 Exp = -.. 4 0.963 R ₁ = 1.1665 d ₁ = 0.122 N ₁ = 1.64769 ν ₁ = 33.80 R ₂ = −49.0204 d ₂ = 0.090 R ₃ = 0.7833 d ₃ = 0.090 N ₂ = 1.71300 ν ₂ = 53.84 R ₄ = 1.4606 d ₄ = 0.026 _{N 3 = 1.58144 ν 3 = 40.75} R 5 = 0.4492 d 5 = 0.144 R 6 = ∞ d 6 = 0.278 R 7 = -0.4268 d 7 = 0.200 N 4 = 1.80518 ν 4 = 25.43 R 8 = 11.2447 d 8 = 0.240 N _{5 = 1.77250 ν 5 = 49.60 R} 9 = -0.6963 d 9 = 0.004 R 10 = -8.8437 d 10 = 0.080 N 6 = 1.77250 ν 6 = 49.60 R 11 = -1.3846 d 11 = 0.004 R 12 = 1.6707 d 12 = 0.078 N ₇ = 1.60311 ν ₇ = 60.70 R ₁₃ = −7.2030 d ₁₃ = ^* variable R ₁₄ = −1.9048 d ₁₄ = 0.020 N ₈ = 1.51742 ν ₈ = 52.41 R ₁₅ = 0.8654 d ₁₅ = 0.015 R ₁₆ = 1.1251 d ₁₆ = 0.116 N ₉ = 1.69680 ν ₉ = 55.53 R ₁₇ = −1.6927 When the object distance d ₀ = ∞ d ₁₃ = 0.074 When the object distance d ₀ = 1.728, that is, when the photographing magnification β = −0.5 d ₁₃ = 0.710 Effect) The lens of the present invention has such a configuration, It is possible to realize a short-distance photographing lens which has a large aperture, a very long back focus and an exit pupil, and excellent aberration correction from infinity to 1/2 times.

[Brief description of the drawings]

1, 6, and 11 show Embodiments 1 and 2 according to the present invention.
3, a lens configuration diagram at infinity shooting state 3, FIG. 7, FIG.
FIG. 12 shows the Seidel aberration coefficient of the first, second, and third embodiments in the infinity photographing state. FIGS. 3, 8, and 13 show the first, second, and third embodiments.
Coefficient of Seidel aberration at 1/2 × magnification of FIG. 4, FIG.
FIG. 14 is an aberration diagram of the first, second, and third embodiments at infinity photographing, and FIGS. 5, 10, and 15 are diagrams of the first, second, and third embodiments at a photographing magnification of 1/2. It is an aberration figure. SA: spherical aberration CM: coma aberration AS: astigmatism DS: distortion aberration PT: Petzval L: axial chromatic aberration T: chromatic aberration of magnification Principal wavelength: 587.56 nm Second wavelength: 460 nm

Claims (2)

(57) [Claims] 1. An object comprising an I-th lens unit having a positive refractive power, a stop, a II-th lens unit having a positive refractive power, and a III-lens group having a positive refractive power in order from the side where light enters. When focusing from a distance infinity to a short distance, the first and second lens units and the diaphragm are extended as one unit. The first lens unit is a first lens unit of the positive lens and a negative meniscus lens having a concave surface facing the image side. The second lens unit includes a second lens unit, a second lens unit, a third lens unit that is a cemented lens of a negative lens having a concave surface facing the object side and a positive lens having a convex surface facing the image side, and a fourth lens unit and a fifth lens unit, respectively. The third lens group,
A sixth lens group, which is a compound lens of at least one concave lens and one convex lens, f: Focal length of the entire system f: Composite focal length of the I-th lens group If: Composite focal length of the II-th lens group II D ₃ : Combination of the third group in the II-th lens group, a cemented lens of a concave lens and a convex lens Thickness Ds ₃ : Distance from the stop to the _third group in the second lens group ν ₁ : Satisfies each condition of the first group, and has a long back focus and a long exit pupil. Large aperture ratio lens. 2. An object comprising an I-th lens unit having a positive refractive power, a stop, a II-th lens unit having a positive refractive power, and a III-lens group having a positive refractive power, in order from the light incident side. When focusing from infinity to infinity, the first and second lens units and the aperture are extended as one unit. The first lens unit is composed of the first lens unit and the positive lens having a convex surface facing the object side. The second lens group is a cemented lens composed of a negative lens having a concave surface facing the object side and a positive lens having a convex surface facing the image side. Group, and a fourth group of positive lenses, respectively.
The fifth lens group, the third lens group includes a sixth lens unit that is a compound lens of at least one concave lens and one convex lens, f: Focal length of the entire system f: Composite focal length of the I-th lens group If: Composite focal length of the II-th lens group II D ₃ : Combination of the third group in the II-th lens group, a cemented lens of a concave lens and a convex lens Thickness Ds ₃ : Distance from the stop to the _third group in the second lens group ν ₁ : Satisfies each condition of the first group, and has a long back focus and a long exit pupil. Large aperture ratio lens.