JPH11287952A - Rear focus zoom lens - Google Patents

Abstract

(57) [Problem] To provide a rear focus type zoom lens having a wide angle of view, having four lens groups as a whole, performing focusing with a fourth group, making the entire lens system small. SOLUTION: In order from the object side, there are four lens groups of a first group having a positive refractive power, a second group having a negative refractive power, a third group having a positive refractive power, and a fourth group having a positive refractive power. Moving the second lens unit to the image plane side to perform zooming from the wide-angle end to the telephoto end, and moving a part or the whole of the fourth lens unit to change the image plane fluctuation due to zooming or a change in the distance of the subject. A zoom lens having a glass block disposed between the fourth unit and the image plane, wherein each lens unit is appropriately set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear focus type zoom lens, and more particularly, to a rear lens and an image forming surface (CC).
D) Used in video cameras, still video cameras, broadcast cameras, etc. that cover an ultra wide angle range while ensuring a long back focus and exit pupil where a glass block such as a color separation prism or filter enters between the camera and D). The present invention relates to a large-diameter rear-focusing zoom lens having a variable magnification ratio of about 3 and an F-number of about 1.8.

[0002]

2. Description of the Related Art In recent years, as home video cameras and the like have become smaller and lighter, remarkable progress has been made in miniaturization of zoom lenses for image pickup. The emphasis is on simplification. As one of means for achieving these objects, the first object side
There is known a so-called rear focus type zoom lens which performs focusing by moving a lens group other than the group. In general, the rear-focus type zoom lens has a smaller effective diameter of the first group than a zoom lens that performs focusing by moving the first group, and it is easy to reduce the size of the entire lens system. In addition, close-up shooting, particularly very close-up shooting, can be performed. Further, since a relatively small and lightweight lens group is moved, there is an advantage that the driving force of the lens group is small and quick focusing can be performed.

For example, Japanese Patent Application Laid-Open No. 63-44614 discloses such a rear focus type zoom lens in which a positive first lens group (having a positive refractive power) and a negative second lens group are arranged in this order from the object side. , A negative third lens group, and a positive fourth lens group. The second lens group is moved to perform zooming, and the third lens group corrects the image plane variation accompanying zooming. Also disclosed is a zoom lens that performs focusing.

In Japanese Patent Application Laid-Open No. 63-278013, in order from the object side, a positive first lens group, a negative second lens group, a weak third lens group, and a positive fourth lens group. A zoom lens that has four lens groups, performs zooming by moving a second lens group, and corrects image plane variation due to zooming and performs focusing with the fourth lens group is disclosed.

[0005] Also, Japanese Patent Application Laid-Open No. Sho 62-206516,
JP-A-63-29718, JP-A-62-2152
No. 25, Japanese Unexamined Patent Publication No. Sho 62-24213, etc. have a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group in this order from the object side. A zoom lens is disclosed in which the two lens groups are moved to perform zooming, and the fourth lens group corrects image plane fluctuations accompanying zooming and performs focusing. Also, JP-A-4-43311, JP-A-4-153615, and JP-A-5-191
No. 65, Japanese Patent Application Laid-Open No. Hei 5-27167, Japanese Patent Application Laid-Open No. Hei 5-60973, and the like, in a zoom lens composed of four lens groups of the type described above, the fourth lens group is replaced by one convex lens (positive lens) or An example constituted by two convex lenses is disclosed.

Japanese Patent Application Laid-Open No. Hei 5-60974 discloses a zoom lens in which the fourth lens group is composed of two concave and convex lenses in a zoom lens composed of four lens groups of the type described above.

Further, JP-A-55-62419, JP-A-62-24213, and JP-A-62-25222.
No. 5, JP-A-56-114920,
-200113, JP-A-4-242707, JP-A-4-343313, JP-A-5-297
In the publications such as Japanese Patent Publication No. 275/275, in a zoom lens composed of four lens groups of the type described above, the third lens group and the fourth lens group are each composed of two positive lenses and negative lenses in the embodiment. Is disclosed.

In Japanese Patent Laid-Open No. 5-72475,
In a zoom lens composed of four lens groups of the type described above, two lenses, a concave lens and a convex lens, are arranged on the object side of the first lens group, thereby achieving a wide-angle zoom lens.

[0009] Further, with the high performance (digitalization) of video decks, the quality of video cameras has been improved.
As one of the methods, high image quality is achieved by image separation by a color separation optical system. A zoom lens suitable for that is disclosed in, for example, JP-A-5-72474 and JP-A-6-624.
51199, JP-A-6-337353, JP-A-6-347697, JP-A-7-199069
JP, JP-A-7-270684, JP-A-7-3
It has been proposed in JP-A-18804, JP-A-9-281390, JP-A-9-281391, and the like.

[0010]

As described above, generally, in a zoom lens, in order to achieve a reduction in the front lens diameter and the size of the entire system, a so-called distance focusing (focusing) by the first lens group is required. The rear focus method is more suitable.

However, the above-mentioned Japanese Patent Application Laid-Open No. 63-446 discloses
In Japanese Patent Application Laid-Open No. 14, the moving space of the third lens group disposed before the stop must be ensured, and there is a limit in reducing the overall length of the lens and the diameter of the front lens.

Also, in Japanese Patent Application Laid-Open No. 63-278013, all of the embodiments achieve the third lens unit by making the third lens unit have a negative refractive power. There was a tendency for the fluctuation to increase.

JP-A-62-206516, JP-A-62-215225, JP-A-62-2423, JP-A-63-29718, JP-A-4-02
No. 6811, JP-A-4-88309, JP-A-4-242707 and JP-A-4-343313, and JP-A-4-43311 and JP-A-4-43311.
JP-A-153615, JP-A-5-19165, JP-A-5-27167, and JP-A-5-609
No. 73, Japanese Patent Application Laid-Open No. 5-60974, Japanese Patent Application Laid-Open
Even in Japanese Patent Application Laid-Open No. 297275, it is difficult to obtain a sufficient back focus for arranging a color separation prism in the lens configuration, and the angle of view at the wide-angle end is not limited to an ultra-wide angle range.

Further, JP-A-55-62419, JP-A-56-114920, and JP-A-3-20011
In the example disclosed in Japanese Patent Publication No. 3 (1993), the first lens group or the third lens group also moves with zooming, so that the lens barrel structure is complicated and a small wide-angle zoom lens is achieved. was difficult. Japanese Patent Application Laid-Open No. Hei 5-72475 discloses a so-called wide converter type in which two concave and convex lenses are arranged on the object side of the first lens group. It is at an inadequate level for achieving high image quality to be achieved using color separation prisms.

[0015] Also, JP-A-5-72474, JP-A-6-51199, JP-A-6-337353, JP-A-6-347697, and JP-A-7-199.
Japanese Patent Application Laid-Open Nos. 069, 7-270684, 7-318804, 9-281390, and 9-281391 ensure a back focus assuming a three-color separation prism. Nevertheless, none of the examples was ultra-wide-angle such that the half angle of view at the wide-angle end satisfied 40 ° or more.

The present invention particularly relates to Japanese Patent Application Laid-Open Nos. 6-511199 and 6-337353, which have been previously proposed by the present applicant.
JP, JP-A-7-270684, JP-A-7-3
With respect to the improvements of JP-A-18804, JP-A-9-281390, and JP-A-9-281391, optical elements such as prisms and filters for color separation and optical elements for the purpose of protecting the zoom lens unit are sufficiently large to accommodate them. Rear focus zoom lens that has an excellent back focus, good optical performance over the entire zoom range and the entire object distance range, and is capable of imaging in an ultra wide angle range of 40 ° or more at a half angle of view. For the purpose of providing.

[0017]

According to the present invention, there is provided a rear focus type zoom lens comprising: (1-1) a first unit having a positive refractive power, a second unit having a negative refractive power, and a positive refraction in order from the object side. The fourth lens unit includes a third lens unit having a positive refractive power and a fourth lens unit having a positive refractive power. The second unit is moved to the image plane side to perform zooming from the wide-angle end to the telephoto end. A zoom lens that corrects an image plane variation caused by a distance variation of the fourth group by moving a part or the whole of the fourth group, and arranges a glass block between the fourth group and the image plane, Has two lens groups, a eleventh lens group having a negative refractive power and a twelfth lens group having a positive refractive power. The eleventh lens group has at least two negative meniscus lenses whose concave surfaces face the image plane. The twelfth lens unit includes a positive lens, a cemented lens of a negative meniscus lens having a concave surface facing the image side, and a positive lens, and a positive lens. When the air spacing between the 11th and 12th groups is L and the focal lengths of the 1st and 2nd groups are f1 and f2, respectively, 0.3 <L / f1 <1.0 ‥‥‥ (1a) It is characterized by satisfying the following conditional expression: 1.9 <f1 / | f2 | <4.3 ‥‥‥ (2a)

(1-2) First positive refractive power from the object side
A fourth lens group including a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power. From the telephoto end to the telephoto end, and corrects the image plane fluctuation caused by the magnification change or the distance change of the object by moving a part or the entirety of the fourth lens unit. A zoom lens in which a glass block is disposed, wherein the third group includes a meniscus-shaped negative 31st lens having a concave surface facing the image surface side and a cemented lens 3a of a positive 32nd lens and a negative 33rd lens. And the air distance between the 31st lens and the cemented lens 3a is d, and the focal length of the third group is f
When 3, it is characterized by satisfying the following conditional expression: 0.06 <d / f3 <0.25 ‥‥‥ (3a).

(1-3) First positive refractive power in order from the object side
A fourth lens group including a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power. From the telephoto end to the telephoto end, and corrects the image plane fluctuation caused by the magnification change or the distance change of the object by moving a part or the entirety of the fourth lens unit. A zoom lens having a glass block disposed therein, wherein the second group includes a meniscus-shaped negative 21st lens, a negative 22nd lens, a positive 23rd lens, and both lens surfaces each having a concave surface facing the image plane side. The focal length at the wide-angle end is Fw, and the focal length of the second group is f.
When 2, it satisfies the following conditional expression: 1.7 <| f2 | / Fw <3.6 ‥‥‥ (4a)

(1-4) First positive refractive power in order from the object side
A fourth lens group including a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power. From the telephoto end to the telephoto end, and corrects the image plane fluctuation caused by the magnification change or the distance change of the object by moving a part or the entirety of the fourth lens unit. A zoom lens in which a glass block is disposed, wherein the first group includes two lens groups, an eleventh group having a negative refractive power and a twelfth group having a positive refractive power, and the eleventh group is arranged on an image side. The twelfth group includes a positive lens, a positive lens or a cemented lens of a negative lens and a positive lens, and a positive lens, and the second group includes a negative lens. Lens, a negative lens, a negative lens, and a positive lens, the focal length of the i-th lens unit is fi, and the entire system at the wide-angle end is Assuming that the point distance is Fw, the following conditional expression is satisfied: −5.0 <f1 / f2 <−0.5ｂ (1b) −5.0 <f2 / Fw <−1.0 ‥‥‥ (2b) It is to be.

(1-5) First positive refractive power in order from the object side
A fourth lens group including a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power. From the telephoto end to the telephoto end, and corrects the image plane fluctuation caused by the magnification change or the distance change of the object by moving a part or the entirety of the fourth lens unit. A zoom lens in which a glass block is disposed, wherein a first group includes a first lens unit having a negative refractive power and a first lens unit having a positive refractive power.
The second lens unit has two lens groups, the eleventh lens group includes at least two meniscus-shaped negative lenses with the concave surface facing the image surface side, and the twelfth lens group has a positive lens and a concave surface on the image surface side. The second lens unit has a focal length of f2, a focal length of the entire system at the wide-angle end is Fw, and an infinity object is focused at the wide-angle end. When the back focus at the time is bFw, the following condition is satisfied: 5 <bFw / Fw <9 ‥‥‥ (1c) -4 <f2 / Fw <-2 ‥‥‥ (2c)

(1-6) First positive refractive power in order from the object side
A fourth lens group including a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power. From the telephoto end to the telephoto end, and corrects the image plane fluctuation caused by the magnification change or the distance change of the object by moving a part or the entirety of the fourth lens unit. A zoom lens in which a glass block is disposed, wherein the third group includes a meniscus-shaped negative 31st lens having a concave surface facing the image surface side and a cemented lens 3a of a positive 32nd lens and a negative 33rd lens. When the focal length of the third lens unit is f3 and the focal length of the entire system at the wide-angle end is Fw, the following condition is satisfied: 30 <f3 / Fw <60 (3c). .

[0023]

FIG. 1, FIG. 3, FIG. 5, FIG. 7, FIG.
11, 13, 15, 17, 19, 21, and 23 are lens cross-sectional views of Numerical Examples 1 to 12 of the rear focus type zoom lens according to the present invention, and FIGS. 8, FIG. 10, FIG. 12, FIG. 14, FIG. 16, FIG. 18, FIG.
FIGS. 0, 22, and 24 are aberration diagrams of Numerical Examples 1 to 12 of the rear focus type zoom lens according to the present invention. In the aberration diagrams, (A) shows the wide-angle end, and (B) shows the telephoto end.

In the figure, L1 is a first lens unit having a positive refractive power, L2 is a second lens unit having a negative refractive power, L3 is a third lens unit having a positive refractive power, and L4 is a positive lens.
Denotes a fourth group having a positive refractive power. SP is an aperture stop,
It is arranged in or near the third unit L3. G is a glass block such as a color separation system, a face plate, and a filter (crystal filter, infrared filter). IP
Is the image plane.

In this embodiment, at the time of zooming from the wide-angle end to the telephoto end, the second lens unit is moved to the image plane side as indicated by an arrow, and the image plane fluctuation caused by zooming is caused by projecting the fourth lens unit to the object side. It is corrected by moving it while having a trajectory.

Also, a rear focus type is adopted in which the fourth unit is moved on the optical axis to perform focusing. A solid line curve 4a and a dotted line curve 4b of the fourth lens group shown in the same figure show the image plane fluctuation caused by zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at a short distance, respectively. The movement locus for correction is shown. The first and third units are fixed during zooming and focusing, but may be moved as needed.

In the present embodiment, the fourth unit is moved to correct the image plane fluctuation caused by zooming, and the fourth unit is moved to perform focusing. In particular, as shown by curves 4a and 4b in the same figure, the zoom lens is moved so as to have a convex locus toward the object side when zooming from the wide-angle end to the telephoto end. Thereby, the space between the third and fourth units is effectively used, and the overall length of the lens is effectively reduced.

In this embodiment, for example, when focusing from an object at infinity to an object at a short distance at the telephoto end, the fourth unit is moved forward as indicated by a straight line 4c in FIG.

The zoom lens according to the present embodiment employs a zoom system in which a virtual image formed by a combined system of the first and second units is formed on the photosensitive surface by the third and fourth units. In the present embodiment, by adopting the rear focus method as described above in comparison with a conventional so-called four-group zoom lens in which the first group is extended and focused, the performance deterioration due to the eccentric error of the first group is prevented. An increase in the effective diameter of one lens group is effectively prevented.

By arranging the aperture stop in or near the third lens unit, fluctuations in aberration due to the movable lens unit are reduced, and the distance between the lens units in front of the aperture stop is shortened to reduce the diameter of the front lens. Is easily achieved.

The rear focus type zoom lenses shown in Numerical Examples 1 to 12 have the above-described lens configuration as a basic configuration.

(A) Next, the features of the lens configuration of Numerical Embodiments 1 to 4 in FIGS. 1, 3, 5, and 7 will be described.

(A-1) In Numerical Examples 1 to 4, based on the above-described basic configuration, the first lens unit is composed of two lens units, namely, a lens unit having a negative refractive power and a lens unit having a positive refractive power. Wherein the eleventh unit has at least two meniscus negative lenses having a concave surface facing the image surface side, and the twelfth unit has a positive lens and a meniscus negative lens having a concave surface facing the image surface And a cemented lens of a positive lens and a positive lens.
a) and (2a) are satisfied.

(A-2) In Numerical Examples 1 to 4, based on the above-mentioned basic configuration, the third group is composed of a meniscus negative 31st lens having a concave surface facing the image surface side. It consists of a cemented lens 3a consisting of a 32nd lens and a negative 33rd lens, and satisfies the conditional expression (3a).

(A-3) In Numerical Examples 1 to 4, based on the above-described basic configuration, the second group is composed of a negative meniscus twenty-first lens having a concave surface facing the image surface side. 22nd lens,
The positive 23rd lens, and the negative 2nd lens with both lens surfaces concave
It consists of four lenses and satisfies the conditional expression (4a).

In each of Numerical Embodiments 1 to 4, a so-called four-group rear-focusing zoom lens is used. In order to secure a long back focus, a substantially afocal magnification constituted by the first, second, and third groups is required. This is made possible by reducing the size and increasing the focal length of the fourth lens unit. For this purpose, the focal length of the first lens unit must be shortened. At this time, the first lens unit and the second lens unit that simply shorten the focal length of the first lens unit may mechanically interfere with each other. Thus, in the present embodiment, by configuring the first lens unit as described above, the principal point position of the first lens unit is pushed toward the second lens unit, and a desired relationship between the first lens unit and the second lens unit is obtained.

More specifically, the eleventh lens unit is composed of three negative meniscus eleventh, twelfth, and thirteenth lenses having a concave surface facing the image plane, and the twelfth lens unit is a positive lens. A fourteenth lens, a cemented lens 1a of a meniscus negative fifteenth lens with a concave surface facing the image side and a positive sixteenth lens;
It consists of a positive seventeenth lens.

In the case of this lens configuration, the principal point position of the lens group is pushed out of the image plane side of the lens group.
Even if the interval between the principal points of the first and second lens units is set to a negative value, no mechanical interference occurs between them. Therefore, it is possible to create a retro-type lens system even at the zooming portion, and it is possible to increase the amount of light beams emitted from the third lens unit in a substantially afocal manner. For this reason, the focal length of the entire system is made short (wide angle) and a long back focus can be ensured without imposing too much load on the focal length of the fourth lens unit.

Incidentally, the cemented lens 1a may be constituted by a single positive lens (the same applies to the following Numerical Examples 5 to 12). Then, one embodiment (A-1) satisfies the conditional expressions (1a) and (2a), another embodiment (A-2) satisfies the conditional expression (3a), and another embodiment (A-1) A
3) satisfies the conditional expression (4a).

Next, the above-mentioned conditional expressions (1a), (2a),
The technical meaning of (3a) and (4a) will be described.

Conditional expression (1a) is a condition necessary for extruding the principal point in the lens arrangement of the first lens unit. Exceeding the lower limit value causes the principal point to be insufficiently extruded. , The desired back focus cannot be obtained, or the required wide angle of view cannot be obtained. On the other hand, when the value exceeds the upper limit, the power of the negative lens in the first lens unit is excessively biased toward the front surface of the first lens unit, so that distortion is strongly generated and good high image quality cannot be obtained.

Conditional expression (2a) shows the relationship between the required focal length ratios of the first and second lens units under such conditions. If the lower limit value is exceeded, the refractive power of the first lens unit becomes too strong. The refracting power of the negative lens arranged on the object side of the first group also increases accordingly, and also negative distortion is strongly generated, which makes correction difficult, which is not preferable. If the value exceeds the upper limit, the required afocal magnification cannot be obtained, so that the focal length of the entire system, which is the object of the present invention, cannot be shortened and a long back focus cannot be secured.

Further, if the numerical range of the conditional expression (2a) satisfies the conditional expression of 2.4 <f1 / | f2 | <3.5 (2aa), it is possible to perform aberration correction more favorably. Becomes

Conditional expression (3a) is that, even in the third lens unit, the principal point position is pushed to the image plane side as much as possible, and the image plane position generated by the magnification change between the first and third lens units is brought closer to the image plane side. Accordingly, there is an effect that the focus plane, which is a conjugate position with the fourth lens unit, is pushed toward the image plane side of the lens, and the back focus can be extended to a desired length by the effect.

If the interval is shorter than the lower limit of conditional expression (3a), it becomes difficult to secure a desired length of back focus while shortening the focal length of the entire system. If the aperture is opened too much, the light beam diverging from the second lens unit diverges greatly in the third lens unit, and the lens diameters of the third and subsequent lens units become undesirably large. Further, when the numerical range of conditional expression (3a) is set to 0.07 <d / f3 <0.17 ‥‥‥ (3aa), aberration correction can be performed more favorably.

Conditional expression (4a) specifies the power of the variable power unit for achieving a zoom lens for an ultra wide angle.
When the refractive power is weaker than the upper limit, the approximate afocal magnification in the above-described variable power unit cannot be sufficiently increased, and it is difficult to secure a desired back focus length. If it becomes too strong, the Petzval sum increases negatively, making it difficult to secure a wide angle of view. Further, the numerical range of conditional expression (4a) is set as follows: 1.7 <| f2 | / Fw <3.0 (4a
If a) is satisfied, aberration correction can be performed more favorably.

Incidentally, in Numerical Examples 1 to 4, that is,
In order to obtain better optical performance in (A-1), (A-2) or (A-3), at least one of the following conditions should be satisfied.

(A1) In order to maintain the Petzval sum, which tends to increase negatively, and to achieve a flat image surface, the materials of the three negative eleventh, twelfth, and thirteenth lenses of the first group should be selected. The average value of the refractive indices of the first lens group is NA1,
Assuming that the average value of the refractive index of the material of the twenty-fourth lens is NA2, it is preferable that 1.60 <NA1 ‥‥‥ (5a) 1.80 <NA2 <1.89 ‥‥‥ (6a).

(A2) To secure a long exit pupil,
The stop is arranged between the negative 31st lens and the positive 32nd lens in the group. However, since the requirements for the exit pupil position vary depending on the configuration of the color separation prism, the stop is arranged before and after the third group. May be.

(A3) The eleventh unit comprises three negative meniscus eleventh, twelfth, and thirteenth lenses having a concave surface facing the image plane, and the twelfth unit comprises a positive fourteenth lens. A cemented lens 1a of a meniscus negative fifteenth lens and a positive sixteenth lens with the concave surface facing the image surface side,
The second group includes a negative twenty-first lens, a negative twenty-second lens, a positive twenty-third lens, and a negative twenty-fourth lens having a concave surface facing the image surface side.
The third group includes a meniscus negative 31st lens having a concave surface facing the image surface side, and a cemented lens 3a of a positive 32nd lens and a negative 33rd lens.

(A4) The fourth unit is a positive meniscus 41th lens having a convex surface facing the image surface side, a negative 42nd lens having a concave surface facing the image surface side, and a positive 42th lens having both convex lens surfaces. Forty-third
A cemented lens 4a with the lens, and a positive 44th lens with both lens surfaces being convex. It is.

Next, FIG. 9, FIG. 11, FIG. 13, FIG.
The features of the lens configurations of Numerical Examples 7 to 9 will be described.

(A-1) Numerical Examples 5 to 9 are based on the above-mentioned basic structure, and the first lens unit is composed of two lens units, an eleventh lens unit having a negative refractive power and a twelfth lens unit having a positive refractive power. The eleventh group has at least two meniscus-shaped negative lenses with the concave surface facing the image plane side, and the twelfth group has a positive lens, a positive lens or a cemented lens of a negative lens and a positive lens, The second lens unit includes a positive lens, a negative lens, a negative lens, a negative lens, and a positive lens.
b) and (2b) are satisfied.

More specifically, in Numerical Examples 5, 6, and 7 shown in FIGS. 9, 11, and 13, the eleventh lens group is a meniscus negative eleventh, twelfth, or twelfth lens element having a concave surface facing the image surface side. The twelfth lens group includes three negative lenses of thirteen lenses. The twelfth lens group includes a positive fourteenth lens, a cemented lens 1a formed by a meniscus negative fifteenth lens having a concave surface facing the image surface side and a positive sixteenth lens, First
It consists of 7 lenses.

In the numerical embodiments 8 and 9 shown in FIGS. 15 and 17, the eleventh lens unit is composed of negative meniscus eleventh and twelfth lenses whose concave surfaces face the image plane side. A cemented lens 1 of a positive fourteenth lens, a meniscus negative fifteenth lens having a concave surface facing the image side, and a positive sixteenth lens
a, consisting of a positive seventeenth lens.

In Numerical Examples 5, 6, 8, and 9, the second group is a negative meniscus twenty-first lens having a concave surface facing the image plane side.
It comprises a negative twenty-second lens, a negative twenty-third lens whose both lens surfaces are concave, and a positive twenty-fourth lens whose both lens surfaces are convex.

In the seventh embodiment, the second lens unit is a meniscus negative twenty-first lens having a concave surface facing the image surface side.
The second lens is composed of two negative lenses, a negative twenty-third lens whose both lens surfaces are concave, and a positive twenty-fourth lens whose both lens surfaces are convex, of which the twenty-third lens and the twenty-fourth lens are cemented lens 2a
It consists of.

In Numerical Embodiments 5 to 9, all spherical lenses are used. However, by using a lens having an aspherical surface, it is possible to further improve the performance and brighten the Fno. In particular, by using a lens having an aspheric surface for the third lens group, it is possible to reduce the number of lenses, and at the same time, it is possible to effectively correct spherical aberration and the like. Further, by using a lens having an aspheric surface for the fourth lens group, coma aberration and the like can be effectively corrected.

By setting as described above,
Ensuring sufficient back focus space for optical elements such as color separation prisms and optical elements intended to protect the zoom lens unit, while providing good optical performance over the entire zoom range and all object distance ranges, A rear-focusing zoom lens capable of imaging an ultra-wide angle range of 40 ° or more at a half angle of view has been obtained.

Next, the technical meaning of the conditional expressions (1b) and (2b) will be described.

Conditional expression (1b) relates to the other of the focal lengths of the first lens unit and the second lens unit, and is for maintaining a long and excellent optical performance with a long back focus while achieving compactness. is there. When the focal length of the second lens group is increased beyond the lower limit of conditional expression (1b) and the focal length of the first lens group is reduced, the amount of movement of the second lens group is increased, and the total lens length and the front lens diameter are reduced. It becomes difficult to reduce the size. In addition, a problem arises in that the amount of movement of the fourth lens group near the telephoto end increases, and the fluctuation of aberration during zooming increases. Conversely, if the value exceeds the upper limit, it becomes difficult to satisfactorily correct various aberrations such as distortion.

The conditional expression (2b) relates to the focal length of the second lens group. If the focal length of the second lens group becomes shorter than the upper limit of conditional expression (2b), the Petzval sum increases in the under direction, and it becomes difficult to correct aberrations such as image plane tilt. Conversely, if the focal length of the second lens group becomes longer than the lower limit, the amount of movement of the second lens group will increase, and the diameter of the front lens will become too large. In order to obtain better optical performance in Numerical Examples 5 to 9, that is, in (A-1), it is preferable to satisfy at least one of the following conditions.

(B1) The third unit is composed of a meniscus negative 31st lens having a concave surface facing the image surface side, and a cemented lens 3a of a positive 32nd lens and a negative 33rd lens. is there.

(B2) The fourth unit is a positive meniscus 41th lens having a convex surface facing the image surface side, a negative 42nd lens having a concave surface facing the image surface side, and a positive 42th lens having both convex surfaces. Forty-third
A cemented lens 4a with the lens and both lens surfaces are composed of a convex positive 44th lens.

(B3) The combined focal length of the 21st and 22nd lenses is f2a, the combined focal length of the 23rd and 24th lenses is f2b, and the combined focal length of the first, second, and third groups. Is f123 and the focal length of the entire system at the telephoto end is fT. 2.5 <f3 / f4 <9９ (3b) -0.5 <f2a / f2b <1 ‥‥‥ (4b) -0. 5 <fT / f123 <0 (5b)

Conditional expression (3b) relates to the ratio of the focal length of the third lens group to the focal length of the fourth lens group. This is for maintaining the optical performance.

If the focal length of the third lens unit is reduced below the lower limit of the conditional expression (3b), it becomes difficult to correct a change in spherical aberration caused by zooming or during focusing. In addition, problems such as difficulty in securing a sufficient back focus, shortening of the exit pupil at the intermediate zoom position, and an increase in the amount of movement of the fourth lens unit, resulting in a large variation in aberrations during zooming and focusing. .

Conversely, if the focal length of the third lens group is increased beyond the upper limit, the divergence of the light beam emitted from the third lens group is increased, the effective diameter of the fourth lens group is increased, and the lens becomes heavier. Problems such as the inability to perform focusing occur.

Condition (4b) relates to the retro ratio in the second lens unit. If the retro ratio is increased beyond the upper limit of the conditional expression (4b), the Petzval sum becomes undersized, and it becomes difficult to correct aberrations such as image plane tilt. On the other hand, when the diameter is smaller than the lower limit, the front principal point of the second lens group is considerably located on the image plane side, and the principal point interval with the first lens group must be increased. There is a problem of increasing the size.

Condition (5b) relates to the degree of parallelism (afocal degree) of the axial light beam emitted from the third lens group. When the convergence of the on-axis light flux becomes higher than the upper limit value of the conditional expression (5b), the astigmatism difference at a close object becomes large, and the meridional image plane becomes insufficiently corrected.

Conversely, if the divergence of the on-axis light beam is increased beyond the lower limit, the height of incidence on the fourth lens group is increased, and a problem arises that a large amount of spherical aberration occurs.

(B4) As described above, conditional expression (1)
b) to (5b) increase the back focus (the distance from the final lens surface excluding the glass block to the image plane) to provide a good optical performance over the entire zoom range and the entire object distance range, This is a condition for satisfying good optical performance, which enables imaging in an ultra wide angle range of 40 ° or more in view angle, but more preferably −4.0 <f1 / f2 <−1.0１．０ (1bb) − 4.0 <f2 / Fw <-2.0 {(2bb) 3.0 <f3 / f4 <7.0} (3bb) -0.3 <f2a / f2b <0.8} (4bb) -0.4 <fT / f123 <-0.1 (5bb)

(B5) To provide good optical performance over the entire zoom range and all object distance ranges, and to capture an ultra wide angle range of 40 ° or more at a half angle of view, and to satisfy good optical performance. , The average value of the refractive index of the negative lens in the second lens group is na
When 2. The condition 1.75 <na2 ‥‥‥ (6b) is satisfied.

The conditional expression (6b) relates to the configuration of the material of the negative lens in the second lens unit for zooming. It is necessary to reduce the amount, but this may increase the negative Petzval sum and impair the flatness of the image plane.

In view of the above, conditional expression (6b) is used to prevent the Petzval sum from increasing when the refractive power of the second lens unit is increased, and to maintain good image plane characteristics in the second lens unit. This is for appropriately setting the refractive power of the materials of the three negative lenses. If conditional expression (6b) is not satisfied, it becomes difficult to satisfactorily correct the fluctuation of the field curvature due to the zooming.

(B6) As described above, it is desirable to satisfy the above-mentioned conditional expression in order to satisfy an excellent optical performance capable of imaging an ultra-wide angle range of 40 ° or more at a half angle of view. To satisfy the performance, -3.7 <f1 / f2 <-1.2 -3.8 <f2 / Fw <-2.4 3.1 <f3 / f4 <6.1 -0.28 <f2a It is desirable to satisfy the following conditional expression: /f2b<0.7−0.37<fT/f123<−0.1 1.80 <na2

Next, the features of the lens configurations of Numerical Examples 10 to 12 shown in FIGS. 19, 21 and 23 will be described.

(C-1) Numerical embodiments 10 to 12 are based on the above-described basic configuration. The first lens unit includes two lens units, an eleventh lens unit having a negative refractive power and a twelfth lens unit having a positive refractive power. The eleventh group has at least two meniscus negative lenses having a concave surface facing the image plane side, and the twelfth group has a positive meniscus negative lens having a concave surface facing the image surface. It consists of a cemented lens with a positive lens, and a positive lens.
(2c) is satisfied.

(C-2) Numerical examples 10 to 12 are based on the above-mentioned basic structure. The third unit is a meniscus negative 31st lens having a concave surface facing the image surface side, and a positive 32nd lens. It is composed of a cemented lens 3a consisting of a lens and a negative 33rd lens, and satisfies the conditional expression (3c).

In Numerical Embodiments 10 to 12, the so-called four-group rear-focusing type zoom lens has a substantially afocal magnification constituted by the first, second, and third groups in order to secure a long back focus. This is made possible by reducing the size and increasing the focal length of the fourth lens unit. For this purpose, the focal length of the first lens unit must be shortened. At this time, the first lens unit and the second lens unit that simply shorten the focal length of the first lens unit may mechanically interfere with each other. Thus, in the present embodiment, by configuring the first lens unit as described above, the principal point position of the first lens unit is pushed toward the second lens unit, and a desired relationship between the first lens unit and the second lens unit is obtained.

The eleventh unit is composed of three meniscus negative eleventh, twelfth, and thirteenth lenses each having a concave surface facing the image side.
The twelfth lens group includes a positive fourteenth lens,
It is composed of a cemented lens 1a of a meniscus negative fifteenth lens with a concave surface facing the image surface side and a positive sixteenth lens, and a positive seventeenth lens.

In the case of this lens configuration, the principal point position of the lens group is pushed out of the image plane side of the lens group.
Even if the interval between the principal points of the first and second lens units is set to a negative value, no mechanical interference occurs between them. Therefore, it is possible to create a retro-type lens system even at the zooming portion, and it is possible to increase the amount of light beams emitted from the third lens unit in a substantially afocal manner. For this reason, the focal length of the entire system is made short (wide angle) and a long back focus can be ensured without imposing too much load on the focal length of the fourth lens unit.

Next, the technical meaning of the conditional expressions (1c) to (3c) will be described.

Conditional expression (1c) is a condition necessary for obtaining a sufficient back focus (the distance from the final lens surface to the image surface when the glass block G is removed) for the interchangeable lens. When the back focus exceeds the value and the back focus becomes longer, the divergence of the light flux from the third lens group to the fourth lens group increases, the fourth lens group becomes large, and the fourth lens group is used for image plane correction and focusing. The load on the moving actuator increases, and at the same time, the fluctuation of aberrations during movement of the fourth lens group also increases.

If the length is shorter than the lower limit, it becomes difficult to secure a space for an optical element such as a color separation prism. Conditional expression (2c) specifies the power of the zooming unit for achieving a zoom lens for an ultra-wide-angle lens. When the refractive power is weaker than the upper limit, the afocal magnification in the zooming unit is sufficiently increased. It is difficult to secure the desired length of the back focus because it cannot be increased, and if the refractive power becomes too strong beyond the lower limit, the Petzval sum increases in the negative direction, thereby securing a wide angle of view. It will be difficult to do.

The conditional expression (3c) is also a condition necessary for obtaining a sufficient back focus for the interchangeable lens. If the focal length of the third lens group becomes shorter than the upper limit, the light beam from the third lens group diverges, the fourth lens becomes larger, and the aberration variation becomes larger. It is difficult to secure a sufficient back focus. In order to favorably correct not only axial chromatic aberration but also chromatic aberration of magnification, it is important to balance the achromaticity of the entire system. For that purpose, the positive 32nd lens of the third group is used. And the negative 33rd lens are preferably cemented lenses.

In order to obtain better optical performance in Numerical Examples 10 to 12, ie, in the configuration (c-1) or (c-2), at least one of the following conditions must be satisfied. Is good.

(C1) At least one aspherical surface is provided in the negative lens of the eleventh group. This makes it possible to satisfactorily correct distortion occurring near the wide-angle end.

(C2) The eleventh lens unit is composed of three negative meniscus eleventh, twelfth, and thirteenth lenses having a concave surface facing the image plane, and the twelfth lens is an aspheric surface. It is to have.

According to this, the manufacturing cost can be reduced as compared with the case of using a large-diameter first aspherical surface, and the off-axis light beam passes through the end of the lens rather than the lens on the image side. , Is very effective for distortion.

(C3) The air spacing between the eleventh and twelfth lens units is L, and the focal lengths of the first and third lens units are f1 and f1, respectively.
f3, the third unit includes a meniscus negative 31st lens having a concave surface facing the image surface side, and a cemented lens 3a of a positive 32nd lens and a negative 33rd lens. 0.2 where d is the air gap from the cemented lens 3a
<L / f1 <1 ‥‥‥ (4c) 0.02 <d / f
3 <0.1 ‥‥‥ (5c).

Conditional expression (4c) is a condition necessary for extruding the principal point in the structure of the first lens unit of the present invention. Exceeding the lower limit value results in insufficient extrusion of the principal point.
The focal length relationship of the second lens group cannot be maintained, so that a desired back focus cannot be obtained or a necessary wide angle of view cannot be obtained. On the other hand, when the value exceeds the upper limit, the power of the negative lens in the first lens unit is excessively biased toward the front surface of the first lens unit, so that distortion is strongly generated and good high image quality cannot be obtained.

Conditional expression (5c) is that even in the third lens unit, the principal point position thereof is pushed to the image plane side as much as possible, and the image plane position generated by zooming between the first and third lens units is brought closer to the image plane side. Accordingly, there is an effect that the focus surface, which is a conjugate position with the fourth lens unit, is pushed toward the image plane side of the lens, and the back focus can be extended to a desired length by the effect. If the interval becomes shorter than the lower limit of this conditional expression, it becomes difficult to secure a desired length of back focus while shortening the focal length of the entire system. The light beam diverging from the group largely diverges in the third group, which is unfavorable because the lens diameter of the third and subsequent groups increases.

(C4) By setting as described above, it is possible to maintain a back focus space and provide excellent optical performance, and at the same time, a rear focus capable of imaging a super wide angle range of 45 ° or more at a half angle of view. You can achieve a type of zoom lens,
In order to further improve the performance, it is desirable to set each conditional expression as follows.

6.0 <bFw / Fw <8.0 (1 cc) -3.0 <f2 / Fw <-2.2 (2 cc) 30.0 <f3 / Fw <50.0 ‥‥ (3cc) 0.40 <L / f1 <0.90 ‥‥ (4cc) 0.04 <d / f3 <0.07 ‥‥ (5cc) (c5) Also, Petzval sum that tends to increase negatively In order to maintain a good image plane and achieve a flat image surface, the average value of the refractive indices of the materials of the three negative eleventh, twelfth, and thirteenth lenses of the first group is set to NA1, and the second group is made of A meniscus negative twenty-first lens, a negative twenty-second lens, a positive twenty-third lens, and a negative twenty-fourth lens having both concave lens surfaces, each having a concave surface facing the image surface side, are provided. When the average value of the refractive indices of the materials of the twenty-first, twenty-second, and twenty-fourth lenses is NA2, 1.60 <NA1 (6c) 1 It is preferable to satisfy the 75 <NA2 <1.89 ‥‥‥ (7c).

(C6) Capable of imaging in an ultra-wide angle range of 45 ° or more at a half angle of view In order to satisfy good optical performance, it is desirable to satisfy the above-mentioned conditional expression. 6.5 <bFw / Fw <7.5-2.9 <f2 / Fw <-2.5 35.0 <f3 / Fw <50.0 0.60 <L / f1 <0. 80 0.045 <d / f3 <0.065 2.62 <NA1 1.79 <NA2 <1.89 It is preferable to satisfy the following conditional expression.

(C7) The fourth unit is a positive meniscus 41th lens having a convex surface facing the image surface side, a negative 42nd lens having a concave surface facing the image surface side, and both positive and negative lens surfaces are convex. Forty-third
A cemented lens 4a with the lens and both lens surfaces are composed of a convex positive 44th lens.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the radius of curvature of the ith lens surface in order from the object side, Di is the ith lens thickness and air spacing in order from the object side, and Ni and νi are the ith lens in order from the object side. Are the refractive index and Abbe number of the glass. In the numerical examples, the last five lens surfaces indicate an optical filter, a face plate, and the like, but these may be omitted if necessary. The aspherical shape is when the X axis is in the optical axis direction, the H axis is perpendicular to the optical axis, the traveling direction of light is positive, R is the paraxial radius of curvature, and B, C, D and E are aspherical coefficients. ,

[0099]

(Equation 1) This is represented by “E-0X” is “× 10 ^−X ”
Means Tables 1 to 3 show the relationship between the above-described conditional expressions and various numerical values in the numerical examples.

[0100]

[Outside 1]

[0101]

[Outside 2]

[0102]

[Outside 3]

[0103]

[Outside 4]

[0104]

[Outside 5]

[0105]

[Outside 6]

[0106]

[Outside 7]

[0107]

[Outside 8]

[0108]

[Outside 9]

[0109]

[Outside 10]

[0110]

[Outside 11]

[0111]

[Outside 12]

[0112]

[Table 1]

[0113]

[Table 2]

[0114]

[Table 3]

[0115]

According to the present invention, by setting each element as described above, sufficient optical elements such as prisms and filters for color separation and optical elements for protecting the zoom lens unit can be accommodated. Achieving a rear-focusing zoom lens that has a back focus, has excellent optical performance over the entire zoom range and the entire object distance range, and can capture images in an ultra-wide angle range of 40 ° or more at a half angle of view can do.

[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 an aberration diagram of a numerical example 1 of the present invention.

FIG. 3 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 4 is an aberration diagram of a numerical example 2 of the present invention.

FIG. 5 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 6 is an aberration diagram of a numerical example 3 of the present invention.

FIG. 7 is a sectional view of a lens according to a numerical example 4 of the present invention.

FIG. 8 is an aberration diagram of a numerical example 4 of the present invention.

FIG. 9 is a sectional view of a lens according to a numerical example 5 of the present invention.

FIG. 10 is an aberration diagram of a numerical example 5 of the present invention.

FIG. 11 is a sectional view of a lens according to a numerical example 6 of the present invention.

FIG. 12 is an aberrational diagram of Numerical Example 6 of the present invention.

FIG. 13 is a sectional view of a lens according to a numerical example 7 of the present invention.

FIG. 14 is an aberration diagram of a numerical example 7 of the present invention.

FIG. 15 is a sectional view of a lens according to a numerical example 8 of the present invention;

FIG. 16 is an aberration diagram of a numerical example 8 of the present invention.

FIG. 17 is a sectional view of a lens according to a numerical example 9 of the present invention;

FIG. 18 is an aberration diagram of a numerical example 9 of the present invention.

FIG. 19 is a sectional view of a lens according to a numerical example 10 of the present invention.

FIG. 20 is an aberration diagram of a numerical example 10 of the present invention.

FIG. 21 is a sectional view of a lens according to a numerical example 11 of the present invention;

FIG. 22 is an aberrational diagram of Numerical Example 11 of the present invention.

FIG. 23 is a sectional view of a lens according to a twelfth embodiment of the present invention;

FIG. 24 is an aberration diagram of a twelfth numerical embodiment of the present invention.

[Explanation of symbols]

 L1 1st lens group L11 11th lens group L12 12th lens group L2 2nd lens group L3 3rd lens group L4 4th lens group IP image plane SP stop d d-line g g-line ΔS sagittal image plane ΔM meridional image plane

Claims (15)

[Claims] 1. A lens system comprising: a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power. Then, the second lens unit is moved to the image plane side to change the magnification from the wide-angle end to the telephoto end, and the image plane fluctuation caused by the zooming or the distance change of the object is moved partially or entirely in the fourth group. A zoom lens in which a glass block is disposed between the fourth group and the image plane.
The two groups are the 11th group of negative refractive power and the 12th group of positive refractive power.
The eleventh group has at least two meniscus-shaped negative lenses with a concave surface facing the image surface side, and the twelfth group has a positive lens, a meniscus-shaped meniscus shape with a concave surface facing the image surface side When the air gap between the eleventh and twelfth groups is L, and the focal lengths of the first and second groups are f1 and f2, respectively, 0.3 <L / f1 <1.01.9 <f1 / | f2 | <4.3. A rear focus type zoom lens, characterized by satisfying the following conditional expression. 2. A lens system comprising: a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power. Then, the second lens unit is moved to the image plane side to change the magnification from the wide-angle end to the telephoto end, and the image plane fluctuation caused by the zooming or the distance change of the object is moved partially or entirely in the fourth group. A zoom lens having a glass block disposed between the fourth group and the image plane, wherein the third group is a meniscus negative 31st lens having a concave surface facing the image plane.
A cemented lens 3a of a positive 32nd lens and a negative 33rd lens, and the 31st lens and the cemented lens 3a
Where d is an air distance from the lens unit, and f3 is the focal length of the third lens unit, the following conditional expression is satisfied: 0.06 <d / f3 <0.25. 3. A lens unit comprising: a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power. Then, the second lens unit is moved to the image plane side to change the magnification from the wide-angle end to the telephoto end, and the image plane fluctuation caused by the zooming or the distance change of the object is moved partially or entirely in the fourth group. A zoom lens having a glass block disposed between the fourth group and the image plane, wherein the second group is a meniscus negative 21st lens having a concave surface facing the image plane.
When a lens, a negative twenty-second lens, a positive twenty-third lens, and a negative twenty-fourth lens whose both lens surfaces are concave, and the focal length at the wide-angle end is Fw and the focal length of the second group is f2, A rear focus type zoom lens characterized by satisfying the following conditional expression: 1.7 <| f2 | / Fw <3.6. 4. The lens system according to claim 1, wherein the eleventh lens unit includes three negative meniscus lenses having a concave surface facing the image surface.
2 or 3 rear focus zoom lens. 5. A lens unit comprising a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power. Then, the second lens unit is moved to the image plane side to change the magnification from the wide-angle end to the telephoto end, and the image plane fluctuation caused by the zooming or the distance change of the object is moved partially or entirely in the fourth group. A zoom lens having a glass block disposed between the fourth lens unit and the image plane, wherein the first lens unit includes a lens unit having a negative refractive power and a lens unit having a positive refractive power. The eleventh group has at least two negative meniscus lenses having a concave surface facing the image plane side, and the twelfth group has a positive lens, a positive lens or a negative lens and a positive lens. The second group includes four lenses, a negative lens, a negative lens, a negative lens, and a positive lens. Assuming that the focal length of the i-th group is fi and the focal length of the entire system at the wide-angle end is Fw, a conditional expression of -5.0 <f1 / f2 <-0.5 -5.0 <f2 / Fw <-1.0 A rear focus zoom lens characterized by satisfying the following conditions. 6. The second group comprises a meniscus negative 21st lens, a negative 22nd lens, a negative 23rd lens, and both positive and negative 24th lenses, each having a concave surface facing the image surface side. 6. The rear focus type zoom lens according to claim 5, wherein: 7. The third unit is composed of a meniscus negative 31st lens having a concave surface facing the image surface side, and a cemented lens 3a of a positive 32nd lens and a negative 33rd lens. The rear focus type zoom lens according to claim 5, wherein 8. The fourth lens unit includes a positive meniscus 41th lens having a convex surface facing the image surface side, a negative 42nd lens having a concave surface facing the image surface side, and a positive 42nd lens having both convex lens surfaces. 7. The rear focus type zoom lens according to claim 5, wherein a cemented lens 4a with the 43 lens and a positive 44th lens having both lens surfaces are convex. 9. The combined focal length of the 21st and 22nd lenses is f2a, the combined focal length of the 23rd and 24th lenses is f2b, and the combined focal length of the first, second, and third groups is f123, when the focal length of the entire system at the telephoto end is fT, the following condition must be satisfied: 2.5 <f3 / f4 <9-0.5 <f2a / f2b <1-0.5 <fT / f123 <0 5. The method according to claim 5, wherein:
Or 8 rear focus zoom lens. 10. The eleventh lens unit includes two negative meniscus negative eleventh and twelfth lenses each having a concave surface facing the image surface side, or a meniscus negative first negative lens having a concave surface facing the image surface side.
The rear focus type zoom lens according to any one of claims 5 to 9, comprising three negative lenses of a first, a twelfth and a thirteenth lens. 11. A first group having a positive refractive power in order from the object side,
The zoom lens includes four lens units, a second unit having a negative refractive power, a third unit having a positive refractive power, and a fourth unit having a positive refractive power. The second unit is moved to the image plane side to be telephoto from the wide-angle end. Zooming to the edge is performed, and the image plane variation due to the zooming or the distance variation of the object is corrected by moving a part or the whole of the fourth unit, and a glass block is provided between the fourth unit and the image plane. Wherein the first group has two lens groups, an eleventh group having a negative refractive power and a twelfth group having a positive refractive power, and the eleventh group has a concave surface on the image plane side. The twelfth group includes at least two meniscus-shaped negative lenses directed toward the lens, and the twelfth group includes a positive lens, a cemented lens formed of a meniscus-shaped negative lens having a concave surface facing the image surface side, and a positive lens. The focal length of the second lens unit is f2, the focal length of the entire system at the wide-angle end is Fw, and the back focus at the wide-angle end is an in-focus object at infinity. When set to bFw 5 <bFw / Fw <9 -4 <f2 / Fw <rear-focusing type zoom lens and satisfies -2 following condition. 12. A first group having a positive refractive power in order from the object side,
The zoom lens includes four lens units, a second unit having a negative refractive power, a third unit having a positive refractive power, and a fourth unit having a positive refractive power. The second unit is moved to the image plane side to be telephoto from the wide-angle end. Zooming to the edge is performed, and the image plane variation due to the zooming or the distance variation of the object is corrected by moving a part or the whole of the fourth unit, and a glass block is provided between the fourth unit and the image plane. Wherein the third group is a meniscus negative third lens having a concave surface facing the image surface side.
One lens, a cemented lens 3a of a positive 32nd lens and a negative 33rd lens, and the focal length of the third group is f
3. When the focal length of the entire system at the wide-angle end is Fw, the following condition is satisfied: 30 <f3 / Fw <60. 13. The rear-focusing zoom lens according to claim 11, wherein at least one aspheric surface is provided on the negative lens of the eleventh group. 14. The eleventh unit is composed of a meniscus negative eleventh, twelfth, and thirteenth lens having a concave surface facing the image surface side.
14. The rear-focusing zoom lens according to claim 13, comprising two negative lenses, wherein said twelfth lens has an aspheric surface. 15. The air gap between the 11th and 12th lens units is L, and the focal lengths of the first and third lens units are f1 and f, respectively.
3. The third group is composed of a meniscus negative 31st lens having a concave surface facing the image surface side, and a cemented lens 3a of a positive 32nd lens and a negative 33rd lens. 11. The optical system according to claim 11, wherein a condition of 0.2 <L / f1 <1 0.02 <d / f3 <0.1 is satisfied, where d is an air distance from the cemented lens 3a.
2, 13 or 14 rear focus zoom lenses.