JP2001337265A - Photographing lens utilizing floating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photographing lens utilizing floating by which aberration fluctuation caused by the change of photographing magnification is excellently compensated in the case of focusing from an infinity object to a short-distance object and having a large aperture ratio at which peripheral light quantity is sufficiently secured. SOLUTION: This photographing lens is provided with two lens groups, that is, a 1st lens group G1 which consists of a 1a-th positive or negative lens group, a diaphragm and a 1b-th positive lens group and is positive as a whole and a 2nd lens group G2 which is positive in order from an object side. The 1a-th lens group is provided with at least one positive lens L2 whose convex surface faces to the object side and at least one negative lens L3 whose intense concave surface faces to an image side, and the 1b-th lens group is provided with at least one doublet consisting of a negative lens L4 whose intense concave surface faces to the object side and a positive lens L5. In the case of focusing from the infinity object to the short-distance object, the 1st lens group G1 is extended and also the 2nd lens group G2 is extended by a moving amount less than that of the 1st lens group G1 so as to perform focusing, and the lens satisfies a specified conditional expression.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photographing lens for forming an image on an image pickup device, particularly a video camera, etc., by using a so-called floating method to perform good aberration correction over a wide range from an object at infinity to a close object. The present invention relates to a large-aperture-ratio photographing lens suitable for the present invention.

[0002]

2. Description of the Related Art Conventionally, a macro lens or a micro lens (hereinafter, referred to as a macro lens) is mainly used for photographing an object at infinity to a close object, particularly a close object, in a photographic camera or a video camera. ")
There is a lens called. The macro lens is designed so that higher optical performance can be obtained, particularly when focusing on a close object, as compared with a general photographing lens. The macro lens is also used for shooting from an object at infinity to an object at a short distance. In general, increase the shooting magnification with a macro lens,
In other words, focusing on a short-distance object causes spherical aberration, field curvature,
Aberration fluctuations such as coma aberration increase. For this reason, it becomes difficult to satisfactorily correct these aberration fluctuations on the high magnification side. Further, spherical aberration and coma have a small F-number, that is, if a bright lens system is used, aberration correction becomes more difficult.

Therefore, the lens system is divided into a plurality of groups, each group is moved at different speeds along the optical axis at the time of focusing, and a sufficient optical performance is maintained at the time of focusing on a short-distance object. Floating type photographing lenses have been proposed. In photographing from an object at infinity to an object at a close distance, a method of correcting aberration fluctuations due to a change in photographing magnification is disclosed in, for example, Japanese Patent Publication No. 7-101253 and Japanese Patent Application Laid-Open No.
No. pp. 139 to 163.

[0004]

The photographic lenses proposed in these publications use a so-called floating system in which two lens groups move at different speeds in the optical axis direction during focusing as described above. Thus, aberration correction is performed relatively well up to high magnification. However, in each case, the spherical aberration greatly fluctuates when focusing on a close object. Regarding coma aberration, in the photographing lens proposed in Japanese Patent Publication No. 7-101253, the fluctuation of coma aberration is particularly large due to light rays passing outside the principal ray with respect to the optical axis. Further, in the photographing lens proposed in Japanese Patent Application Laid-Open No. 63-179308, the fluctuation of coma due to light rays passing both sides of the principal ray with respect to the optical axis is large. Therefore, the photographing lenses proposed in any of the publications have a structure in which coma aberration is suppressed by sacrificing the amount of peripheral light. As a result, the amount of peripheral light is greatly reduced up to the maximum image height, and the amount of peripheral light is not sufficient. The present invention has been made in view of the above-described problem, and uses a floating that favorably corrects aberration variation due to a change in imaging magnification when focusing from an object at infinity to an object at a short distance, and sufficiently reduces the amount of peripheral light. It is an object of the present invention to provide a photographing lens having a large aperture ratio.

[0005]

In order to attain the above object, the present invention provides, in order from the object side, a first lens unit having a weak positive or negative refractive power, a diaphragm having a positive refractive power, and a first lens unit having a positive refractive power. A first lens group having a positive refractive power as a whole, comprising a 1b lens group, and a second lens group having a positive refractive power as a whole.
The first lens group includes at least one positive lens having a convex surface facing the object side and at least one negative lens having a strong concave surface facing the image side; The group has at least one cemented lens of a negative lens and a positive lens with a strong concave surface facing the object side, and when focusing from an object at infinity to an object at a short distance, the first lens group is extended. Focusing is performed by extending the second lens group less than the amount of movement of the first lens group, and when the focal length of the 1a lens group is f1a and the focal length of the entire photographing lens system is f, | f1a / F |> 30 (1) An imaging lens utilizing floating, characterized by satisfying the following conditional expression:

In general, a macro lens capable of performing close-up photography from infinity has a problem in fluctuation of spherical aberration and coma when focusing from an object at infinity to an object at a short distance. That is, the spherical aberration is negatively corrected at the time of focusing from an object at infinity to an object at a short distance, which causes a decrease in optical performance including contrast. Also, coma tends to deteriorate when focusing from an object at infinity to an object at a short distance. Both of the spherical aberration and the coma become more difficult to correct for fluctuations in a bright lens system having a small F-number.

According to the present invention, the above-mentioned configuration is compared with a case where focusing is performed by a so-called whole extension system in which the entire lens system is moved on the optical axis when focusing from an object at infinity to an object at a short distance. The first lens group and the second lens group
The distance between the lens group and the lens group increases. Therefore, it is possible to keep the height of the light beam incident on the second lens group low when focusing from an object at infinity to an object at a short distance. At the same time, the angle of the light beam incident on the second lens group can be reduced as compared with the case where focusing is performed by so-called whole extension. As a result, the coma aberration is efficiently corrected to the maximum image height, so that a sufficient peripheral light amount can be secured. In addition, when focusing is performed by so-called whole extension, in which the first lens unit and the second lens unit are integrally extended, spherical aberration is largely negatively corrected when focusing from an object at infinity to an object at a short distance. For this reason,
As for focusing on a short-distance object, it becomes difficult to obtain sufficient optical performance. However, by adopting a floating method in which the distance between the first lens group and the second lens group is changed, the spherical aberration generated in the first lens group is changed to the opposite sign generated in the second lens group. Can be effectively canceled out by the spherical aberration of. Therefore, deterioration of spherical aberration due to the second lens group can be prevented. Therefore, according to the present invention, it is possible to realize an optical system in which fluctuations of various aberrations such as spherical aberration are suppressed when focusing from an object at infinity to an object at a short distance.

Next, since the lens structure of the present invention is composed of the first lens group having a positive refractive power and the second lens group having a positive refractive power, a sufficient back focus of the entire lens system is obtained. It is difficult, but by defining the refractive power arrangement of each lens group to an appropriate value, the back focus of the entire lens system can be made an appropriate value. Also, the second
The configuration of the lens group is divided into a 2a lens group having a negative refractive power and a 2b lens group having a positive refractive power in order from the object side, and the ratio of the respective focal lengths is set in an appropriate range. Thus, the second lens group has a so-called retrofocus arrangement. This, the 1a-th lens group and the first
By arranging the b lens group effectively, it is possible to obtain a long back focus while the first lens group and the second lens group are both optical systems having a positive refractive power. Further, the second lens group includes:
In order from the object side, a combination of a positive lens with a convex surface facing the object side, a negative lens and a positive lens with a concave surface facing the image side,
Alternatively, in order from the object side, by arranging a combination of a cemented lens and a positive lens of a positive lens having a convex surface facing the object side and a negative lens having a concave surface facing the image surface side, the first lens group remains. It is possible to effectively correct axial chromatic aberration and lateral chromatic aberration.

Next, each conditional expression will be described. Conditional expression (1) is a conditional expression that defines the back focus of the entire photographing lens system. Since a conventional so-called Gaussian type photographing lens is composed of a front group having a positive refractive power and a rear group having a positive refractive power in order from the object side, it is difficult to increase the back focus. On the other hand, in the present invention, by satisfying conditional expression (1), it is possible to employ a so-called modified Gaussian type lens configuration and secure a back focus.

Out of the range of the conditional expression (1),
When the negative refracting power in the lens group is increased, the first lens group has a so-called retrofocus arrangement. For this reason, there is an advantage that the back focus can be long, but it becomes difficult to satisfactorily correct distortion in the entire region from an object at infinity to an object at a short distance. Further, if the range of the conditional expression (1) is deviated, and the positive refractive power in the first lens subunit increases, the back focus becomes extremely short because the first lens subunit and the second lens subunit have positive refractive power. turn into.

In the present invention, the focal length of the second lens subunit is f2a, and the focal length of the second lens subunit is f2a.
When 2b is satisfied, it is preferable to satisfy the following conditional expression: -4 <f2a / f2b <-1.5 (2)

Conditional expression (2) is a condition for maintaining an appropriate group spacing for floating. The present invention includes a first lens group having a positive refractive power from the object side and a second lens group having a positive refractive power. When focusing from an object at infinity to an object at a short distance, the first lens group has the first lens group. A so-called floating operation in which the second lens group is extended less than the first lens group while the lens group is extended. Therefore, at the time of focusing on infinity, it is necessary to set the group interval between the first lens group and the second lens group to an appropriate value. If the upper limit of conditional expression (2) is exceeded and the negative refractive power of the 2a-th lens unit becomes too strong with respect to the refractive power of the 2b-th lens unit, the principal point of the second lens unit will be shifted to the 2a-th lens unit. Since the lens system moves in the image plane direction with respect to the lens group, the overall length of the lens system becomes long, and the entire lens system cannot be made compact, which is not preferable. Conversely, when the value goes below the lower limit of conditional expression (2),
If the negative refractive power of the second lens group becomes too weak with respect to the refractive power of the second lens group, the principal point of the second lens group moves toward the object with respect to the second lens group. For this reason, the distance between the first lens group and the second lens group becomes extremely short, which is not preferable for disposing a movable group for floating.

Hereinafter, numerical embodiments of the taking lens according to the present invention will be described with reference to the accompanying drawings. The basic configuration of the photographic lens system according to the present invention is as follows: a first lens unit having a weak negative refractive power from the object side; a stop; and a first lens unit having a positive refractive power. And a second lens group having a positive refractive power.

(First Embodiment) FIG. 1 is a diagram showing a lens configuration of a taking lens according to a first embodiment when focusing on infinity. The present photographing lens includes, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power. When focusing on an object at a short distance, the first lens group G1 is extended, and at the same time, the second lens group G2 is extended less than the first lens group G1, so-called floating. The first lens group G1 includes, in order from the object side, a biconvex lens L1, a meniscus-shaped positive lens L2 having a convex surface facing the object side, and a meniscus-shaped negative lens L3 having a strong concave surface facing the image surface side. The first lens unit includes a 1a lens unit, an aperture S, and a 1b lens unit including a biconvex lens L6 and a cemented positive lens of a biconcave lens L4 and a biconvex lens L5 with a strong concave surface facing the object side. The second lens group G2 includes a second lens subunit L2 including a meniscus positive lens L7 having a convex surface facing the object side and a meniscus negative lens L8 having a concave surface facing the image surface, and a biconvex lens L9. 2b lens group.

Table 1 shows the specification values of this embodiment. In the overall specifications, f is the focal length of the entire lens system, and FNO is F
The numbers 2ω represent the photographing angle of view, respectively. In the lens data and variable interval data, β is the shooting magnification,
D0 is the distance from the object to the first surface of the lens under each shooting condition, r is the radius of curvature of the lens, d is the distance between the lens surfaces, and n is d.
The refractive index at the line (λ = 587.6 nm), and ν indicates the Abbe number at the d line. In the following, the same reference numerals as those in the present embodiment are used in the specification values of all the embodiments. In addition, the unit of the focal length, radius of curvature, surface spacing, and length in the specification table is generally "mm", but the same optical performance can be obtained even if the optical system is proportionally enlarged or reduced. It is not limited to.

[0016]

[Table 1]

FIG. 2 is a diagram showing various aberrations at the time of focusing on infinity according to the present embodiment, and FIG. 3 is a diagram showing various aberrations at the time of focusing on a close range. In each aberration diagram, Y is the maximum image height, NA is the numerical aperture,
d is d-line (λ = 587.6 nm), g is g-line (λ = 43 nm).
5.6 nm). In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. Regarding the lateral chromatic aberration,
It is shown with reference to the d-line. In the following, the same reference numerals are used in the aberration diagrams of all the embodiments as in the aberration diagrams of the present embodiment. As is clear from the aberration diagrams, it is understood that good optical performance is maintained in focusing from an object at infinity to an object at a close distance. Further, as is clear from the coma aberration diagram, it is understood that the coma aberration is favorably corrected up to the peripheral portion and that a sufficient peripheral light amount is provided.

(Second Embodiment) FIG. 4 is a diagram showing a lens configuration of a taking lens according to a second embodiment when focusing on infinity. The present photographing lens includes, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power. When focusing on a short-distance object, so-called floating is performed in which the first lens group G1 is extended and the second lens group G2 is extended less than the first lens group G1. The first lens group G1 is
In order from the object side, a first-a lens group composed of a biconvex lens L1, a meniscus-shaped positive lens L2 having a convex surface facing the object side, and a meniscus-shaped negative lens L3 having a strong concave surface facing the image plane side, and an aperture stop S, and a 1b-th lens unit including a biconvex lens L6 and a cemented positive lens of a biconcave lens L4 and a biconvex lens L5 with a strong concave surface facing the object side. The second lens group G2 includes a second a lens group including a cemented negative lens composed of a positive meniscus lens L7 having a convex surface facing the object side and a negative meniscus lens L8 having a concave surface facing the image surface. And a second lens group composed of a convex lens L9. Table 2 shows the specification values of this embodiment.

[0019]

[Table 2]

FIG. 5 is a diagram showing various aberrations of the present embodiment when focusing on infinity, and FIG. 6 is a diagram showing various aberrations when focusing on a close range. As is clear from the aberration diagrams, it is understood that good optical performance is maintained in focusing from an object at infinity to an object at a close distance. Further, as is clear from the coma aberration diagram, it is understood that the coma aberration is favorably corrected up to the peripheral portion and that a sufficient peripheral light amount is provided.

(Third Embodiment) FIG. 7 is a diagram showing a lens configuration of a taking lens according to a third embodiment when focusing on infinity. The present photographing lens includes, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power. When focusing on a short-distance object, so-called floating is performed in which the first lens group G1 is extended and the second lens group G2 is extended less than the first lens group G1. The first lens group G1 is
In order from the object side, a first-a lens group composed of a biconvex lens L1, a meniscus-shaped positive lens L2 having a convex surface facing the object side, and a meniscus-shaped negative lens L3 having a strong concave surface facing the image plane side, and an aperture stop S, and a first-b lens unit including a biconvex lens L6 and a cemented positive lens of a biconcave lens L4 and a biconvex lens L5 with a strong concave surface facing the object side. The second lens group G2 includes a second a lens group including a cemented negative lens formed by a meniscus-shaped positive lens L7 having a convex surface facing the object side and a meniscus-shaped negative lens L8 having a concave surface facing the image surface side, and a biconvex lens. 2b consisting of L9
And a lens group. Table 3 shows the specification values of the present embodiment.

[0022]

[Table 3]

FIG. 8 is a diagram showing various aberrations at the time of focusing on infinity in the present embodiment, and FIG. 9 is a diagram showing various aberrations at the time of focusing on a close range. As is clear from the aberration diagrams, it is understood that good optical performance is maintained in focusing from an object at infinity to an object at a close distance. Further, as is clear from the coma aberration diagram, it can be seen that the coma aberration is favorably corrected up to the peripheral portion and that there is a sufficient peripheral light amount.

(Fourth Embodiment) FIG. 10 is a diagram showing a lens configuration of a taking lens according to a fourth embodiment when focusing on infinity. The present photographing lens includes, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power. When focusing on a short-distance object, so-called floating is performed in which the first lens group G1 is extended and the second lens group G2 is extended less than the first lens group. The first lens group G1 includes, in order from the object side, a biconvex lens L1, a meniscus-shaped positive lens L2 having a convex surface facing the object side, and a meniscus-shaped negative lens L3 having a strong concave surface facing the image surface side. First
An a-lens group, a stop S, and a first-b lens group including a biconvex lens L6 and a cemented positive lens of a biconcave lens L4 and a biconvex lens L5 with a strong concave surface facing the object side. The second lens group G2 is, in order from the object side, a 2a lens formed of a cemented negative lens of a meniscus-shaped positive lens L7 having a convex surface facing the object side and a meniscus-shaped negative lens L8 having a concave surface facing the image plane side. The second lens subunit includes a lens group and a second lens group including a biconvex lens L9. Table 4 shows the specification values of the present embodiment.

[0025]

[Table 4]

FIG. 11 is a diagram showing various aberrations at the time of focusing on infinity according to the present embodiment, and FIG. 12 is a diagram showing various aberrations at the time of focusing on a close range. As is clear from the aberration diagrams, it is understood that good optical performance is maintained in focusing from an object at infinity to an object at a close distance. Further, as is clear from the coma aberration diagram, it can be seen that the coma aberration is favorably corrected up to the peripheral portion and that there is a sufficient peripheral light amount.

[0027]

As described above, according to the present invention,
By performing so-called floating under appropriate conditions, when focusing from an object at infinity to an object at a short distance, use floating, which properly corrects aberration fluctuations due to changes in shooting magnification, and secures sufficient peripheral light quantity Thus, a photographing lens having a large aperture ratio can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a lens configuration of an imaging lens according to Example 1 upon focusing on infinity.

FIG. 2 is a diagram showing various aberrations of the first embodiment at the time of focusing on infinity.

FIG. 3 is a diagram showing various aberrations of the first embodiment when focused at a close distance.

FIG. 4 is a diagram illustrating a lens configuration of an imaging lens according to Example 2 upon focusing on infinity.

FIG. 5 is a diagram showing various aberrations of the second embodiment upon focusing on infinity.

FIG. 6 is a diagram illustrating various aberrations of the second embodiment when focused at a close distance.

FIG. 7 is a diagram illustrating a lens configuration of an imaging lens according to Example 3 upon focusing on infinity.

FIG. 8 is a diagram showing various aberrations of the third embodiment when focused on infinity.

FIG. 9 is a diagram illustrating various aberrations when focusing on a close distance in the third embodiment.

FIG. 10 is a diagram showing a lens configuration of a taking lens according to Example 4 when focused on infinity.

FIG. 11 is a diagram showing various aberrations of the fourth embodiment at the time of focusing on infinity.

FIG. 12 is a diagram illustrating various aberrations when focusing on a subject at a close distance in the fourth example.

[Explanation of symbols]

 G1 First lens group G2 Second lens group L1 to L9 Each lens component S Aperture

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 2H087 KA01 LA06 MA09 PA07 PA08 PA18 PA19 PB09 QA02 QA07 QA14 QA21 QA26 QA34 QA42 QA45 RA36

Claims (4)

[Claims] 1. A first lens unit having, in order from an object side, a first lens unit having a weak positive or negative refractive power, a stop, and a first lens unit having a positive refractive power.
The first lens sub-unit includes a lens unit and a second lens unit having a positive refractive power. The first lens unit includes a positive lens having a convex surface facing at least one object side, and at least one image side. The first lens sub-unit has at least one cemented lens of a negative lens having a strong concave surface facing the object side and a positive lens, and has a short distance from an object at infinity. When focusing on an object, the first lens group is extended and the second lens group is extended less than the movement amount of the first lens group to perform focusing, and the focal length of the first lens group is set to f1a. | F1a / f |> 30 (1) where f is the focal length of the entire photographing lens system, and 1 is a photographing lens utilizing floating. 2. The second lens group is divided into a 2a lens group having a negative refractive power and a 2b lens group having a positive refractive power, wherein the focal length of the 2a lens group is f2a, The floating lens according to claim 1, wherein the following conditional expression is satisfied: -4 <f2a / f2b <-1.5 (2) where f2b is the focal length of the 2b lens group. 3. The second lens group includes, in order from the object side,
3. The photographic lens utilizing floating according to claim 1, wherein the photographic lens comprises a positive lens having a convex surface facing the object side, a negative lens having a concave surface facing the image surface side, and a positive lens. 4. The second lens group includes, in order from the object side,
4. The lens according to claim 1, comprising a cemented lens of a positive lens having a convex surface facing the object side, a negative lens having a concave surface facing the image surface side, and a positive lens. 5. Shooting lens that uses floating camera.