JPS6183512A - Zoom lens - Google Patents

Abstract

PURPOSE:To simplify the lens constitution of a relay system by exchanging the lens group of part of the relay system with the other lens group thereby changing the focal length of the entire system while maintaining an image plane in a specified position. CONSTITUTION:The lens group of part of the relay system, for example, a front group 12 having a negative refracting power is exchanged with the lens group 13 having the negative refracting power stronger than the refracting power of the group 12 in the zoom lens disposed with the relay systems 12, 14 on the side nearer the image plane 15 than a variable power part 11, by which the focal length of the entire system is changed while the image plane 15 is maintained in the specified position.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens, and particularly to a zoom lens in which a relay system is arranged behind a variable power section, by replacing some lens groups of the relay system with other lens groups, the entire system can be improved. This relates to a zoom lens that has a different focal length.

Conventionally, there have been zoom lenses that use a so-called built-in extender, which inserts a new lens system into a part of the zoom lens relay system to change the magnification range while maintaining the image plane at a constant position. This method has been proposed in Japanese Patent Application Laid-open No. 49-96741, Japanese Patent Application Laid-Open No. 113753-1980, and the like.

In these publications, the focal length at the wide-angle end zoom position is f, the N zoom ratio is 2, a built-in extension is installed, and the magnification range is changed to m, that is, the focal length is mfW.
-mZfW is proposed. Among these, in Japanese Patent Laid-Open No. 49-96741, an afocal optical path is formed in a relay system, and a built-in extender is inserted into the afocal optical path to change the magnification range. Further, in Japanese Patent Laid-Open No. 52-113753, a built-in extender with negative refractive power is inserted into the relay system to change the range of magnification.

In the zoom lenses proposed in these publications, a new lens group is inserted into the relay system to change the variable magnification range, making the relay system's lens configuration complicated and requiring the insertion of a built-in extender. This tends to cause higher-order aberrations, increase flare components, and degrade optical performance.

SUMMARY OF THE INVENTION An object of the present invention is to provide a zoom lens that can change the focal length range of the entire system, that is, the variable power range, while simplifying the lens configuration of the relay system.

The main feature of a zoom lens for achieving the object of the present invention is that in a zoom lens in which a relay system is arranged closer to the image plane than the variable magnification section, some lens groups of the relay system can be replaced with other lens groups. This allows the focal length of the gold thread to be changed while maintaining the image plane at a constant position.

In the present invention, by adopting such a configuration, the zoom range can be easily changed while simplifying the relay system lens configuration.

Preferably, in the present invention, the relay system is composed of two lens groups, a lens group A having a negative refractive power and a lens group B having a positive refractive power, in order from the object side, and the lens group A is a lens group A having a negative refractive power. The focal length of the entire system is changed by replacing the lens group A' with a lens group A' having a stronger refractive power than that of the lens group A'. In this way, in the present invention, the relay system is of the retro-four-focus type to reduce aberration fluctuations after changing the zoom range, and also to reduce the aperture diameter and the outer diameter of the lens group A'. We are trying to make this happen. As a result, in the present invention, the entire zoom lens can be easily reduced in size and weight.

Further preferably, in the present invention, lens group A'
The lens is constructed of a so-called telephoto lens consisting of a lens group A1' having a positive refractive power and a lens group A2' having a negative refractive power in order from the object side. This makes it possible to extremely reduce the amount of aberrations that occur when changing the magnification range to the long focal length side.

Next, one embodiment of the present invention will be described with reference to each drawing.

FIG. 1(4), 1) is a schematic diagram of an optical system according to an embodiment of the present invention. The same figure (the station is before the change in the magnification range, the same figure (B)
indicates the optical system after changing the magnification range. In the same figure, 1
1 is a variable power unit including a variable power lens group and a focusing lens group;
2 is the front group of the relay system and has negative refractive power. 14 is the rear group of the relay system and has positive refractive power. 15 is an image plane. In this embodiment, by replacing the front group 12 shown in FIG. changing range.

FIGS. 2(4) and 2(B) are explanatory diagrams of the optical arrangement of the thin lens system when changing the zoom range in the zoom lens of the present invention.

Figure (4) shows the optical arrangement before the variable power range changes, and Figure CB) shows the optical arrangement after the variable power range changes. In the figure, 21 is a variable magnification unit, 22 and 23 are a front group of a relay system, 24 is a rear group of a relay system, and 25 is an image plane. φ1 is the refractive power of the variable power unit 21, φ2 is the refractive power of the front group 22, φS is the refractive power of the rear group 24,
φ? is the refractive power of the front group 26, and 11 is the variable power unit 21 and the front group 22.
12 is the principal point interval between the front group 22 and the rear group 24, l, *, , P are the principal point intervals after changing the magnification range, respectively.
△、? are the distances between the front principal point and the rear principal point of the front group 22 and the front group 23, respectively.

Using each of the above symbols, and using the Gaussian brackets [・@@｜] described in the miscellaneous paper "Optics" (published by Japan Society of Applied Physics, Optics Association, Vol. 12, No. 6, 1983), page 484. The following explanation will be given using the focal length f of the gold thread in Fig. 2 (4).
is f-1/(φ1+-'l'1+φ2.-12+φ3]
...obtained from (1). The back focus SF at this time is 5F-(φb-71+φ2.-12)/(
φi+””41+φ2+ '2+φ3〕φ...(2)
You can ask for more. Next, as shown in FIG. 2(B), when the front group 22 is replaced with another lens group 26 and the variable power range is changed, what is the focal length of the entire system after the change? and bank focus SF" are respectively f"-1/[φ1+-'1"
:φP l6φ3〕 ・・φ・・(3) SF9 [φ1+
'I''+φ~-IP)/(φ1.-ki φ2.-l to φ
3]...obtained from (4).

In the present invention, since the image plane is constant before and after the variable magnification range, SF = SF'' * @ @ @ @ (5) Also, if the focal length of the entire system changes by a factor of m, mf-f ＠−＠＠＠(3) And since the total length of the lens remains unchanged, rice rice rice 11 + △ + 12 - z1 + Δ + 12 ... fist (7
). From the above equations (1), (3), and (3), and from equations (2), (4), and (5),
becomes. That is, by satisfying equations (7), (8), and (9), it is possible to achieve a zoom lens in which the focal length of the entire system is changed by a factor of m while maintaining the image plane at a constant position.

In the present invention, it is preferable for aberration correction and adjustment of the lens assembly to configure the variable magnification section so that the light beam exiting the variable magnification section is substantially afocal.

That is, if the refractive power φ1 is configured to be φ1−o, it becomes easy to determine the refractive power arrangement of the subsequent lens group, and furthermore, optical adjustment with the relay system can be easily performed.

In the present invention, the variable power unit is arranged in order from the object side to a focusing lens group,
Of course, there are zoom lenses that consist of a lens group for variable magnification, but also zoom lenses that do not have a lens group for focusing, but are configured so that focusing is achieved by moving a part of the lens group for variable magnification. It can also be successfully applied to lenses.

Further, in the present invention, in order from the object side, the lens group A1' is composed of a lens whose both lens surfaces are convex and a meniscus-shaped lens with a negative refractive power whose convex surface faces toward the image plane side, and the lens group A2 is constituted by If both lens surfaces are made of concave lenses, the amount of aberration generated after changing the zoom range can be reduced despite the simple structure.

As described above, according to the present invention, it is possible to achieve a zoom lens in which the focal length range of the entire system is changed while simplifying the lens configuration of the relay system.

Next, numerical examples of the present invention will be shown. In the numerical examples, Ri is the radius of curvature of the first lens surface in order from the object side, Di is the thickness and air gap of the second lens surface in order from the object side, and Hi and νt are the radius of curvature of the first lens surface in order from the object side. These are the refractive index and Atsube number of the lens glass.

Numerical Example 1 is before changing the zoom range, and Numerical Example 2 is changing the zoom range by replacing the relay system front group (R14 to R19) of Numerical Example 1 with another lens group (R14 to R18). After that.

R27 to R34 in Numerical Example 1 and R26 to R33 in Numerical Example 2 are parallel plane plates such as filters.

Numerical Example 1 F-13,04-58.96 FNO-1:i, 82ω
-45,7~16.1°R34~ Numerical Example 2 F-20,00~59.767NO-1: 2.72%5
0.8~10.5'R32-~D32-0.5N
13-148700 18-65.0R33-~

[Brief explanation of the drawing]

Figures 1W and (B) are schematic diagrams of an optical system according to an embodiment of the present invention, and Figures 2 (4) and (B) are diagrams of the optical system when changing the magnification range of the zoom lens according to the present invention. Explanatory diagrams of the optical arrangement, FIGS. 6 and 5 are lens sectional views of numerical embodiments 1 and 2 of the present invention, FIGS. 4A and 4B, and FIGS. 6 and 4, respectively.
B) is a diagram of various aberrations of Numerical Examples 1 and 2 of the present invention, respectively. In the figure, (4) is a diagram of various aberrations at the wide-angle end, and (B) is a diagram of various aberrations at the telephoto end. In the figure, ■ is the focusing lens group, ■ and ■ are the variable magnification lens group,
■1. ■1" is the front group of the relay system, ■2 is the rear group of the relay system, d is the d-line, g is the g-line, △S is the sagittal image plane, 6M
is the meridional image surface.

Claims (3)

[Claims] (1) In a zoom lens with a relay system placed closer to the image plane than the variable magnification unit, by replacing some of the lens groups in the relay system with other lens groups, the entire system can maintain the image plane at a constant position. A zoom lens characterized by changing the focal length of the lens. (2) The relay system is composed of two lens groups, a lens group A with a negative refractive power and a lens group B with a positive refractive power, in order from the object side, and the lens group A has a refractive power of the lens group A and a lens group B with a positive refractive power. 2. The zoom lens according to claim 1, wherein the focal length of the entire system is changed by replacing the lens group A' with a lens group A' having a different refractive power. (3) A zoom lens according to claim 2, wherein the lens group A' is composed of a telephoto lens.