JPH0792545B2 - Zoom lens with variable magnification range - Google Patents

Description

The present invention relates to a zoom lens having a variable zoom range suitable for a television camera, a video camera, etc., and particularly to a zoom lens group using a space of a relay lens group. By changing the zoom range of the entire system by detachably mounting it to the long focal length side, for example, the back focus is long, and it is suitable for a shooting system such as a color television camera having a three-color separation optical system. The present invention relates to a zoom lens having a variable double range.

(Prior Art) Conventionally, various zoom lens systems have been proposed in which the zoom range of the zoom lens is changed from a normal zoom range to another zoom range having a different focal length. .

Of these, a so-called built-in extender system is widely used in television cameras and the like, in which a variable power lens group is attached to and detached from a fixed relay lens group disposed behind the zoom unit to change the variable power range. This method has the advantages that the zoom range can be changed instantaneously, the back focus of the entire lens system can be kept unchanged, and the total lens length is constant.

A zoom lens using the built-in extender system is proposed in, for example, Japanese Patent Application Laid-Open No. 51-81634 and Japanese Patent Publication No. 58-33528.

Among them, in Japanese Examined Patent Publication No. 58-33528, a zoom lens is composed of a zoom section and a relay lens group, and the relay lens group is composed of a relay front group of negative refracting power and a relay rear group of positive refracting power, At this time, the space between the relay front group and the relay rear group is configured as air or thick parallel plane glass. When there is a front-relay group or parallel-plane glass, the front-relay group and parallel-plane glass are retracted out of the optical path, and a variable power lens group is inserted in the space between them to change the variable power range.

Since this method is advantageous in securing a space for the variable power lens group, it has an advantage that aberration correction is easy and the total lens length can be shortened relatively easily. However, since the diaphragm of the zoom lens of the publication is arranged in front of the compensator of the zoom section, the exit pupil is close in the standard state without the variable power lens group, and the color is increased in the television camera using the three-color separation optical system. Shading occurred and the effective diameter of the post-relay group tended to increase.

For this reason, recently, a zoom lens in which an aperture stop is arranged in front of the relay lens group and the zoom range is changed with the same configuration is often used. However, when the diaphragm is arranged in front of the relay lens group, the diaphragm drive mechanism and the mechanism for attaching and detaching the variable power lens group come close to each other in the optical axis direction, and it is easy for them to interfere with each other, and the positioning and arrangement accuracy of each element is improved. There was a problem that it became very difficult to maintain.

As another method for changing the zooming range of the zoom lens, the relay front group of the relay lens group is fixed, and the parallel plane glass is set in the space between the relay front group and the relay rear group, or when there is parallel plane glass. There is also a method in which a variable power lens group is retracted outside the optical path and a variable power lens group is inserted into the space to change the variable power range.

In this method, since the front lens group of the relay is fixed when the variable power lens group is mounted, the mechanism for attaching and detaching the variable power lens group can be configured to be separated from the diaphragm drive mechanism by the thickness of the front lens group of the relay. Do not approach and interfere.

However, this method has a problem that the diameter of the light beam in the relay lens group increases as the back focus is lengthened, and the diameter of the variable magnification lens group to be inserted increases accordingly.

Furthermore, in order to position the exit pupil far away, it is necessary to dispose a thick parallel plane glass between the front and rear relay groups when the variable power lens group is not attached, which increases the weight of the relay lens group as a whole. There was a problem such as coming up.

(Problems to be Solved by the Invention) According to the present invention, the lens configuration of the relay lens group disposed behind the zoom unit is appropriately set, and a part of the relay lens group is retracted from the optical path. In addition, by inserting the variable power lens group into the space of the relay lens group, it is possible to avoid mutual interference between the detachable mechanism of the variable power lens group and the diaphragm drive mechanism, and to keep the total lens length constant. An object of the present invention is to provide a zoom lens having a variable zoom range that can easily change the zoom range of the entire system while maintaining a long back focus and excellent correction of aberrations.

(Means for solving the problem) A zoom unit having a negative refracting power as a whole, including a lens group having a focusing function and a zooming function in order from the object side, an aperture stop, and fixing at the time of focusing and zooming And a relay lens group having an image forming function, the relay lens group having two lens groups, a relay front group and a relay rear group, with a widest air gap as a boundary. The group is composed of a fixed group of relay front groups having a fixed positive refractive power and a group of relay front groups exchangeable from the optical path, and the group of relay front groups exchanged with the fixed group of relay front groups as well as retracting the group of relay front groups from the optical path. By changing the variable power range of the whole system by inserting a variable power lens group in the optical path between the relay rear group, the focal length of the relay front fixed group fRFF, the infinity object of the zoom unit Focal length at any zoom position when focused Is fZ, and the principal point distance from the rear principal point of the zoom section to the front principal point of the relay front group fixed group is EZ −2.0 ≦ fRFF / (fZ−EZ) ≦ −0.6 (1) To satisfy the condition.

(Embodiment) FIG. 1A is a lens cross-sectional view of an embodiment when zooming is performed in a normal zoom range in a zoom lens having a variable zoom range according to the present invention. The figure shows the zoom position at the wide-angle end, in which F is a focus lens group having a focus function, and V is a variator that performs a magnification change function, and moves linearly on the optical axis. C is a compensator that moves non-linearly on the optical axis in order to correct the image plane variation due to zooming. The focus lens group F, the variator lens V, and the compensator C form a zoom unit Z having a negative refractive power. SP is an aperture stop. R is a relay lens group, which is fixed during focusing and zooming. The relay lens group R is composed of two lens groups, a relay front group RF and a relay rear group RR with the widest air gap as a boundary. Of these, the relay front group RF is a fixed front lens group RFF having a fixed positive refractive power, and a detachable relay front group exchange group that can be exchanged with other lens groups.
It is composed of RFR.

P is a three-color separation optical system including a prism and the like, and is shown as a developed block in the figure. Q is the image plane.

In this embodiment, the variator V and the compensator C are moved to change the magnification. For example, as shown in a numerical embodiment described later, the magnification is changed in the normal magnification range of the zoom ratio 10 with the focal length f = 10 to 100. You have achieved the zoom lens you went to.

When changing the variable power range to another variable power range, as shown in FIG. 1 (B), the relay front group fixed group RFF of the positive refractive power of the relay front group is left, and the relay front group is left. Exchange group RFR
Between the relay front group fixed group RFF and the relay rear group RR in the relay lens group with the variable power lens group E having a refractive power different from that of the relay front group exchange group RFR. It is inserted in the optical path.

As a result, for example, as shown in a numerical example to be described later, the focal length f is changed to twice the long focal length side before the change in magnification, and the change range is changed to f = 20 to 200 as a whole. .

In FIG. 2, S is an aperture driving mechanism, and EA is a variable magnification lens group attaching / detaching mechanism.

As described above, in this embodiment, the relay front group fixed group RFF having a positive refracting power in the relay front group RF is left, and the relay front group exchanging group RFR having a positive or negative refracting power is exchanged for the variable power lens group E. By changing the zoom range, there is little variation in aberration before and after the change,
We have obtained a zoom lens with good optical performance over the entire zoom range. Further, the diaphragm drive mechanism S and the variable power lens attaching / detaching mechanism EA are separated from each other by a predetermined amount so that both mechanisms do not interfere with each other. Then, the incident diameter of the light beam on the variable power lens group is made small so that aberration correction can be easily performed.

In this embodiment, in order to maintain good aberration correction while having a long back focus and to shorten the total lens length, the relay front group fixed group has a focal length of fRFF and the zoom unit has an infinite object. When the focal length at any zoom position when focused on is fZ and the principal point distance from the rear principal point of the zoom section to the front principal point of the relay front group fixed group is EZ, −2.0 ≦ fRFF / (FZ−EZ) ≦ −0.6 (1) It is better to satisfy the condition. Conditional expression (1) is mainly for making the light beam to the variable power lens group substantially afocal to obtain good optical performance while reducing manufacturing errors.

When the lower limit of conditional expression (1) is exceeded and the positive refractive power of the fixed group in the front of the relay becomes too weak, the incident diameter of the light beam to the variable power lens group E increases, which makes it difficult to correct aberrations and changes the variable power. The positive refracting power on the entrance side of the lens group becomes strong, and it becomes difficult to shorten the total lens length. On the contrary, when the positive refractive power of the fixed group in the front of the relay becomes stronger and exceeds the upper limit, the incident diameter of the light beam on the variable power lens group E becomes small and the total lens length is shortened. It becomes difficult to maintain a long back focus before mounting. Further, a strong negative refracting power is required for the relay front group exchange group, and it becomes very difficult to obtain good aberration correction.

In this embodiment, in order to satisfactorily correct various aberrations including chromatic aberration over the entire zoom range and obtain high optical performance, a front lens group in which the relay front group is fixed and a positive lens whose convex surface is directed toward the image side from the object side, or A positive lens with a convex surface facing the object side and a cemented lens in which a positive lens and a negative lens are cemented together, and the relay front group exchange group is composed of at least one cemented lens in which a positive lens and a negative lens are independently or cemented. Good to configure.

Further, it is preferable that the rear lens group is composed of a positive lens having a convex convex convex lens surface, two cemented lenses in which a positive lens and a negative lens are cemented, or a negative lens and a positive lens, and a positive lens.

Further, it is preferable that the interchangeable lens group has at least one positive lens whose both lens surfaces are convex and at least two cemented lenses.

Next, numerical examples of the present invention will be shown. Ri in the numerical examples
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 gap from the object side, Ni and νi
Are the refractive index and Abbe number of the glass of the i-th lens in order from the object side.

(Effects of the Invention) According to the present invention, the relay lens group arranged on the image plane side of the zoom unit is configured as described above, and a part of the lens group is replaced with a variable power lens group. Along with shortening the overall length, ensuring a long back focus, and correcting aberration fluctuations before and after changing the zoom range, and achieving a zoom lens with variable zoom range that has good optical performance over the entire zoom range. be able to.

[Brief description of drawings]

FIGS. 1 and 2 are lens sectional views of Numerical Embodiments 1 and 2 of the present invention, and FIGS. 3 and 4 are Numerical Embodiments 1 and 2 of the present invention, respectively.
FIG. 7 is a diagram of various types of aberration of FIG. In the lens cross-sectional view and the aberration diagram, (A) is before the change of the zoom range and (B) is after the change of the zoom range. In the figure, Z is a zoom unit, F is a focus group, V is a variator, C is a compensator, SP is an aperture stop, R is a relay lens group, RF is a relay front group, RR is a relay rear group, and RFF is a relay front group. A fixed group, RFR is a relay front group exchange group, E is an exchange lens group, P is a color separation optical system, Q is an image plane, S is an aperture drive mechanism, and EA is a variable magnification lens group attachment / detachment mechanism.

Claims (1)

[Claims] 1. A zoom unit having a negative refracting power as a whole including a lens group having a focusing function and a zooming function in order from the object side, an aperture stop, and a fixed imaging function at the time of focusing and zooming. And a relay lens group provided with the relay lens group, wherein the relay lens group has two lens groups of a relay front group and a relay rear group with a widest air gap as a boundary, and the relay front group is a fixed positive lens group. A relay front group fixed group having a refracting power and a relay front group exchange group removable from the optical path, the relay front group exchange group is retracted from the optical path, and the relay front group fixed group and the relay rear group are By changing the zoom range of the entire system by inserting a variable power lens group in the optical path between, the focal length of the fixed group of the relay front group fRFF, arbitrary when focusing on an object at infinity of the zoom section FZ is the focal length at the zoom position of A variable range characterized by satisfying the condition of −2.0 ≦ fRFF / (fZ−EZ) ≦ −0.6, where EZ is the principal point distance from the side principal point to the front principal point of the relay front group fixed group. Variable zoom lens.