JP3352264B2 - Retrofocus type lens and camera having the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retrofocus type lens having a photographing angle of view of about 75 DEG suitable for a 35 mm camera or a video camera and an F number of about 1.8, and a back focus longer than the focal length. Seki was <br/> the camera, especially when the rear lens group in the lens system is moved along the optical axis to perform focus and properly configure the lens system so good optical performance over an object distance range Lyer A retrofocus lens using a focus system and
It relates to a camera having the same.

[0002]

2. Description of the Related Art Conventionally, as a wide-angle photographing lens having a back focus longer than a focal length, a retrofocus (reverse telephoto type) lens preceded by a lens group having a weak positive refractive power or a negative refractive power. Are variously proposed.

For example, Japanese Patent Publication No. Sho 60-34730 proposes a bright retro-focus type lens having a compact lens configuration having a photographic angle of view of about 75 ° to 85 ° and an F-number of about F2.0. In Japanese Patent Application Laid-Open No. 61-144616, spherical aberration and sagittal flare are satisfactorily corrected by using an aspherical surface.
A bright retrofocus lens of about 1.4 has been proposed. In Japanese Patent Publication No. 55-10049, the angle of view is 85 °.
A bright retrofocus type lens having an F number of about F1.4 has been proposed. Various focus methods are used in a retrofocus lens.

For example, in Japanese Patent Publication No. Sho 58-5, a first lens unit having a negative refractive power and a second lens unit having a positive refractive power are provided in order from the object side.
There has been proposed a retrofocus lens that moves both lens units toward the object side while changing the distance between the first and second units when focusing from an object at infinity to an object at a short distance. In Japanese Patent Publication No. 58-26001, a first lens unit having a negative refractive power and a second lens unit having a positive refractive power are provided in order from the object side, and the first lens unit is fixed during focusing from an object at infinity to an object at a short distance. Has proposed a retrofocus type lens that moves only the second group to the object side.

Japanese Patent Application Laid-Open No. 55-143517 discloses that in focusing from an object at infinity to an object at a short distance, only one or two lenses having a positive refractive power disposed closest to the image side of the entire lens system are used. We have proposed a retrofocus type lens that moves to the side. In Japanese Patent Application Laid-Open No. 63-163317, during focusing from an object at infinity to an object at a short distance, only two or three lenses having the negative or positive refractive power arranged closest to the image side among all the lens systems are mutually moved. We have proposed a retrofocus lens that moves to the object side while changing the distance.

[0006]

Generally, a retrofocus type lens has an asymmetric lens configuration as a whole, in which a lens unit having a negative refractive power is disposed in front of a lens unit having a positive refractive power and a lens unit having a positive refractive power is disposed in the rear. Therefore, the amount of various aberrations such as spherical aberration, coma, distortion, and astigmatism increases, and the absolute value of the negative refractive power of the front lens group is increased to secure a long back focus. Therefore, the amount of generation of various aberrations is further increased, and it is generally difficult to correct these various aberrations in a well-balanced manner.

Further, the retrofocus lens tends to increase the diameter of the front lens when increasing the amount of light around the screen. Generally, it is not desirable to move a large, heavy front lens for focusing. In particular, as a photographic lens for a camera with an automatic focus adjustment mechanism, when the focus is adjusted with the front lens, there is a problem that the load on the actuator for focus adjustment becomes large and rapid driving becomes difficult. On the other hand, there is a method using a rear focus system in which a relatively small rear lens group in the lens system is moved to perform focusing.

In general, the rear focus type has a smaller amount of extension of the focusing lens group than the whole focusing type in which the entire lens system is extended, and the focusing lens group is relatively small and light, so that focusing can be performed with a small driving force. Therefore, it is suitable for a camera or the like having an automatic focus detection device. In addition, since the entire length of the lens is always constant even when focusing is performed, there is an advantage that the photographing device is easily held and camera shake hardly occurs.

However, the rear focus type has a larger aberration variation when the focus lens group is moved than the whole focus type in which the entire lens system is extended.
It becomes difficult to satisfactorily correct aberrations over the entire object distance. This tendency is particularly remarkable in a so-called retrofocus lens in which the front group includes a lens group having a negative refractive power and the rear group includes a lens group having a positive refractive power. Increases, astigmatism also worsens, and the optical performance significantly decreases.

The present invention has two lens groups, a first lens group having a positive or negative refractive power and a second lens group having a positive refractive power, and has a back focus longer than the focal length. By properly setting the lens configuration of the second group to be moved, the advantages of the rear focus system are maintained, and aberration fluctuations during focusing over the entire object distance from an object at infinity to an object at a short distance are satisfactorily corrected. It is an object of the present invention to provide a retrofocus type lens having a high optical performance, a shooting angle of view of about 75 °, and an F number of about 1.8 and a back focus longer than the focal length, and a camera having the same.

[0011]

Means for Solving the Problems] retrofocus lens of the invention of claim 1, in turn from the object side, a first lens unit of positive or negative refractive power as a whole, a second lens unit of positive refractive power as a whole The first group has two or three lenses.
The second group is a second d group having a negative refractive power in order from the object side,
A second lens unit having a positive refractive power and a second lens unit having a positive refractive power;
Has three lens groups, during focusing from infinity to a close object, and fixing the first group, said 2d group
The distance between the second lens unit and the second lens unit, and increasing the distance between the second lens unit and the second lens unit.
Move each lens group to the object side to reduce the distance between
And then, the focal length of the first group and the entire system each f1, f
When a, 5 <| is characterized by satisfying the (1) The condition | f1 / f.

[0012]

1 and 2 show a numerical example of the present invention described later .
It is a lens sectional view of 1 and 2 . 3 to 8 show Reference Examples 1 to 3.
FIG. 6 is a lens sectional view of FIG. 9 and 10 are aberration diagrams of Numerical Examples 1 and 2 of the present invention. Figures 11 to 16 are for reference
It is an aberrational figure of Examples 1-6. In the aberration diagrams, (A) shows an infinitely distant object, and (B) shows a short distance when the object distance is 10 times the focal length.

In the drawing, L1 has two or three lenses, and a first group (front group) having weak positive or negative refractive power as a whole, and L2 is a three group which moves on the optical axis during focusing. lens groups 2d, 2e, having a 2f, second group of positive refractive power as a whole (the rear group), SP denotes a stop. 2d is negative refraction
The second group of powers, 2e is the second group of positive refractive power, 2f is positive
Is a second f group having the refractive power of .

The first lens unit L1 comprises a negative meniscus first lens having a convex surface facing the object side, and a positive second lens having both convex lens surfaces.
The second lens unit L2 includes two negative lenses, a negative third meniscus lens having a convex surface facing the object side, a negative fourth lens having both concave lens surfaces, and a positive positive lens having both lens surfaces convex. Fifth
A lens, an aperture stop, a meniscus negative sixth lens having a convex surface facing the image surface side, a meniscus positive seventh lens having a convex surface facing the image surface, and a negative eighth lens having a concave surface facing the object side It has eight lenses: a cemented lens bonded to a lens, a ninth meniscus lens having a convex surface facing the image surface, and a tenth meniscus lens having a convex surface facing the image surface. ing. When focusing from an object at infinity to an object at a short distance, the first unit L1 is fixed, and the lens units 2d, 2e, and 2f of the second unit are moved to the object side as indicated by arrows in the figure.

According to the present invention, the first lens unit having two or three lenses, the first lens unit having two or three lenses, and the first lens unit having a relatively weak positive or negative refractive power. 2
The second group is composed of three lens groups that are further movable on the optical axis. When focusing from an object at infinity to an object at a short distance, the first unit is fixed, and the lens units of the second unit are moved so as to approach the first unit while changing the distance between them. As a result, an extremely good retrofocus lens which has overcome the conventional disadvantages is realized.

In particular, according to the present invention, the first group having a relatively large outer diameter, which is disposed closest to the object side of the retrofocus lens, is fixed at the time of focusing, and the load on the drive member for focus adjustment is reduced. At the same time, the operability of filters and the like generally used in wide-angle lenses is improved.

Also, in the present invention, various aberrations during focusing, particularly coma and astigmatism, which have been difficult to correct with such a retrofocus lens, are reduced, so that a near-infinity object can be corrected. as always satisfactory image even when performing the focus adjustment of the distance the object is obtained a second group
The lens unit is divided into three lens groups, and the distance between these lens groups is appropriately changed to perform focusing. In general, retrofocus lenses have an asymmetric configuration in which a negative refractive power lens group is placed on the object side of the lens system and a positive refractive power lens group is placed on the image side in order to maintain a sufficiently long back focus. In order to correct coma and astigmatism, which are asymmetrical aberrations, at this time, a lens group arranged on the object side and a lens group arranged on the image side It is necessary to appropriately set the shape and the arrangement of. However, since it is necessary to move some of the lens groups for focusing here, there has been a problem that an appropriate arrangement cannot be maintained from an object at infinity to an object at a short distance. come.

Therefore, in the present invention, the increase of the asymmetry aberration is corrected well by moving some of the lens units during focusing and at the same time, by partially changing the distance between the lens units. Symmetry aberrations, that is, increases in spherical aberration and the like are also satisfactorily corrected.

In the present invention, the sixth lens is provided with at least one aspherical surface, so that the asymmetric aberration can be corrected well. Also, the focal lengths of the first lens group and the entire system are respectively f1,
Assuming that f, the condition 5 <| f1 / f | １ ／ (1) is satisfied.

Conditional expression (1) defines the ratio between the fixed focal length f1 of the first lens unit and the focal length f of the entire lens system during focus adjustment. By limiting the refractive power of the group to be relatively weak, mainly the asymmetric aberration is favorably corrected.

If the refractive power of the first lens unit is increased outside the range satisfying the conditional expression (1), the following adverse effects occur.
If the focal length f1 of the first lens unit is negative and has a small absolute value, the asymmetry of the entire lens system becomes strong, making it difficult to correct coma, astigmatism, and the like. The fluctuation of the curvature of field during the adjustment is increased. Conversely, if the focal length f1 of the first lens unit is positive and has a small absolute value, it becomes difficult to maintain the reverse telephoto refractive power arrangement of the entire lens system, and a sufficiently long back focus is maintained. It becomes difficult to do. In addition, since the focal length of the second lens unit is increased, the amount of driving of the lens unit for adjusting the focus is increased, which is disadvantageous in that it is not suitable for downsizing.

In the numerical examples 1 and 2 shown in FIGS. 1 and 2, the second lens unit is a second lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a second lens unit having a positive refractive power. The lens system includes three lens groups of a 2f group, and when focusing from an object at infinity to an object at a short distance, increases the distance between the second d group and the second e group,
Each lens group is moved to the object side so as to reduce the distance between the second lens group and the second lens group.

The second lens unit and the second lens unit are moved together during focusing to simplify the mechanism. 2f
At least one lens surface of the group has an aspherical surface and mainly corrects asymmetric aberrations well. An aperture SP is provided between the second lens group and the second lens group to prevent an increase in the outer diameter of the front lens and the rear lens, and to reduce the size of the entire lens system.

In Reference Examples 1 and 2 shown in FIGS. 3 and 4, the second lens unit is a second lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a second lens unit having a positive refractive power. The lens unit has three lens groups, and when focusing from an object at infinity to an object at a short distance, the distance between the second lens group and the second lens group is reduced.
Each lens group is moved to the object side so as to increase the distance between the group and the second c group.

The second lens group and the second lens group are moved integrally during focusing to simplify the mechanism. 2nd b
At least one lens surface of the group is made aspherical so that asymmetric aberration is well corrected. The aperture SP is set to the second group and the second group.
The entire lens system is miniaturized while preventing an increase in the lens outer diameter of the front lens and the rear lens by being provided between the lens group b.

In Reference Examples 3 and 4 shown in FIGS. 5 and 6, the second group has, in order from the object side, two lens groups: a second i-group having a positive refractive power and a second j-group having a positive refractive power. At the time of focusing from an object at infinity to an object at a short distance, each lens unit is moved to the object side so as to reduce the distance between the second unit and the second unit.

At least one lens surface of the second j group is made aspherical, and mainly asymmetric aberration is favorably corrected. An aperture SP is provided between the second lens unit and the second lens unit to prevent an increase in the outer diameter of the front lens and the rear lens, and to reduce the size of the entire lens system.

In Reference Examples 5 and 6 shown in FIGS. 7 and 8, the second group has, in order from the object side, two lens groups, a second g group having a negative refractive power and a second h group having a positive refractive power. When focusing from an object at infinity to an object at a short distance, each lens group is moved to the object side so as to increase the distance between the second g group and the second h group.

At least one lens surface of the second lens unit has an aspherical surface, and mainly asymmetric aberrations are well corrected. By providing the stop SP in the second h group, an increase in the outer diameter of the front lens and the rear lens is prevented, and the overall size of the lens system is reduced.

Next, Numerical Examples 1 and 2 of the present invention and Reference Examples
Numerical Examples 1 to 6 are shown. In the numerical examples, 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 spacing in order from the object side, and ni and νi are the i-th lens in order from the object side. Are the refractive index and Abbe number of the glass. Aspherical shape is X in the optical axis direction
Axis, the H axis perpendicular to the optical axis, the light traveling direction is positive, and R
Is the paraxial radius of curvature, and B, C, D, and E are aspherical coefficients, respectively.

[0031]

(Equation 1) It is represented by the following expression. “D-0X” means “10 ^−X ”.

[0032]

[Outside 1]

[0033]

[Outside 2]

[0034]

[Outside 3]

[0035]

[Outside 4]

[0036]

[Outside 5]

[0037]

[Outside 6]

[0038]

[Outside 7]

[0039]

[Outside 8]

[0040]

As described above, according to the present invention, there are provided two lens units, a first unit having a positive or negative refractive power and a second unit having a positive refractive power, and the back focus is larger than the focal length. By properly setting the lens configuration of the second group to be moved during focusing in a long retrofocus type lens, while maintaining the advantage of the rear focus type, the focusing of the entire object distance from an object at infinity to a close object is maintained. It is possible to achieve a retrofocus type lens having a high optical performance in which a variation in aberration at the time of correction is excellent and has a shooting angle of view of about 75 ° and an F number of about 1.8 and a back focus longer than the focal length.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 3 is a sectional view of a lens according to a first embodiment of the present invention;

FIG. 4 is a sectional view of a lens according to a reference example 2 of the present invention.

FIG. 5 is a sectional view of a lens according to a third embodiment of the present invention.

FIG. 6 is a sectional view of a lens according to a fourth embodiment of the present invention.

FIG. 7 is a sectional view of a lens according to a fifth embodiment of the present invention.

FIG. 8 is a sectional view of a lens according to a sixth embodiment of the present invention.

FIG. 9 is a diagram showing various aberrations of Numerical Example 1 of the present invention.

FIG. 10 is a diagram showing various aberrations of Numerical Example 2 of the present invention.

FIG. 11 is a diagram showing various aberrations of Reference Example 1 of the present invention.

FIG. 12 is a diagram showing various aberrations of Reference Example 2 of the present invention.

FIG. 13 is a diagram showing various aberrations of Reference Example 3 of the present invention.

FIG. 14 is a diagram showing various aberrations of Reference Example 4 of the present invention.

FIG. 15 is a diagram showing various aberrations of Reference Example 5 of the present invention.

FIG. 16 is a diagram showing various aberrations of Reference Example 6 of the present invention.

[Explanation of symbols]

 L1 First group L2 Second group SP Aperture d d line gg line S. C Sine condition ΔS Sagittal image plane ΔM Meridional image plane

Continuation of the front page (56) References JP-A-63-61213 (JP, A) JP-A-5-188294 (JP, A) JP-A-6-160706 (JP, A) JP-A-57-35821 (JP) JP-A-63-163317 (JP, A) JP-A-57-132112 (JP, A) JP-A-4-118612 (JP, A) JP-A-62-291613 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (5)

(57) [Claims] 1. An optical system comprising , in order from the object side , a first group having a positive or negative refractive power as a whole and a second group having a positive refractive power as a whole . The first group includes two or three lenses. And the second group is a second d group having a negative refractive power and a positive
3rd group of 2e group of refractive power and 2f group of positive refractive power
In focusing from an object at infinity to an object at a short distance, the first unit is fixed, and the second unit and the second unit are fixed .
The distance between the second group and the second group is increased by increasing the interval between the second group and the second group.
Move each lens group to the object side to reduce the distance
And which, when a focal length of the first group and the entire system each f1, f, 5 <| f1 / f | becomes retrofocus lens satisfies the condition. 2. The retrofocus lens according to claim 1 , wherein said second lens group and said second lens group move integrally during focusing. Wherein said first 2f group of at least one lens surface retrofocus lens according to claim 1 or 2, characterized in that an aspherical surface. Wherein said first 2e group and retrofocus lens according to claim 1, 2 or 3, characterized in that an opening stop between the first 2f group. 5. A camera comprising the retrofocus lens according to claim 1 .