JPH03161729A - Zoom lens - Google Patents

Abstract

PURPOSE:To provide the zoom lens which has excellent operability and simple structure and is inexpensive by constituting the movable lens group having a negative refracting power among the relay lens groups of a 3-group constitution having positive, negative and positive refracting powers in such a manner that this lens group can be moved between two positions along the optical axis. CONSTITUTION:The relay lens groups IV, V, VI are constituted of the three lens groups having the refracting powers which are positive, negative and positive successively from an object side. The lens group V having the negative refracting power among the three lens groups is so constituted that this group can moved on the optical axis between the two positions to be the same image plane position VII. Only the focal length of the entire lens system is changed by moving the movable lens group V so as to bring the same to the two positions to constitute the same image plane position VII, by which the zoom region is instantaneously changed. The focal length can be varied while the image plane position VII is held immobile in this way. The zoom lens having the simple structure, the low cost and the good operability is obtd.

Description

[Detailed Description of the Invention] (Industrial Field of Application) The present invention provides a function to change the focal length range of a zoom lens by moving some lens groups of the zoom lens while keeping the image plane position unchanged. The present invention relates to a zoom lens equipped with.

(Prior art and its problems) Changes in the focal length of a zoom lens, for example, when the focal length is 10
The focal length of Kaku~100mm is 15mm~150m.
The following methods are known as methods for changing.

(1) A method in which an attachment lens is attached and detached between the zoom lens body and the image plane.

(2) A method in which parts of the zoom lens that are not involved in forcing and zooming, the so-called relay part of the zoom lens, are replaced.

(3) A method of attaching and detaching an afocal lens system whose absolute value of angular magnification is not 1 to the subject side of the zoom lens body.

(4) A method of attaching and detaching an attachment lens to a part of the zoom lens relay.

(5) A system in which a zoom system is further provided in the relay part of the zoom lens.

In the method (4) above, it is necessary to provide a mechanism for attaching and detaching the attachment lens from the side to the zoom lens body.
There are problems such as the structure of the lens barrel of the zoom lens body is complicated and failures are likely to occur.

The method (5) above is called a double zoom method, and the focal length range can be changed continuously while keeping the image plane position unchanged, and the overall optical length does not change. It's a useful tool.

However, this system has problems in that the zoom mechanism is also included in the relay of the zoom lens, making it extremely complex in structure, thick in shape, and high in price.

Therefore, the present invention was made to solve the problems of the conventional models described above, and its purpose is to provide a simple structure that can change the focal length while keeping the image plane position unchanged. To provide a zoom lens that can be provided at a low price and has good operability.

(Means for Solving the Problems) In the present invention according to the above object, in a zoom lens having a focusing lens group, a zooming lens group, and a relay lens group from the object world side, the relay lens group has a refractive power on the object world side. It is composed of three lens groups that are more positive, negative, and positive, and among these three lens groups, the lens group that has negative refractive power moves on the optical axis between two positions that are the same image plane position. It is characterized by being provided in a movable movable lens group.

(Function) Among the three lens groups of the relay lens group, a lens group having negative refractive power is provided in a movable lens group that is movable between two positions that are the same image plane position. By moving the movable lens group to the two positions mentioned above, only the focal length of the entire lens system changes, making it possible to instantly change the zoom range. (Embodiment) A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a sectional view of a zoom lens according to an embodiment of the present invention, showing its basic state.

The zoom lens has a focusing lens group I that is movable for focusing, a zooming lens group ■, ■ that is movable for zooming, and a relay lens group that is fixed during focusing and zooming. This relay lens group consists of, from the object world side, a fixed lens group (■) with positive refractive power, a movable lens group (V) with negative refractive power that is moved when changing the focal length, and a positive refractive power. Fixed lens groups (2) with (1) and (2) are sequentially arranged. ■ indicates the image plane.

In the lens system, the focal length changes from 1 to 7.6009 by moving the zoom lens groups (1) and (2).

Table 1 shows the standardized data of the above lens.

Table 1 Ri is the radius of curvature of the i-th surface, Di is the axial wall thickness or axial air gap between the i-th surface and the i+1-th surface, ν is the dispersion value, and N is the refractive index (d-line). di, d2, and d3 indicate the distance between lenses that changes due to zooming, and data of an example thereof is shown at the bottom of Table 1.

The total sum is, of course, constant. d4 and d5 are fixed lens group ■ and movable lens group V, respectively.
indicates the distance between the movable lens group V and the fixed lens group ■, and when the zoom lens is at the spacing position shown in Table 1, the focal length can be changed from 1 to 1 by moving the zooming lens groups ■ and ■. It changes to 7.6009.

In this embodiment, the movable lens group V is movable on the optical axis. When the movable lens group V is moved a predetermined distance from the position shown in FIG. 1 (Table 1) toward the image field side (rearward), the image is again formed on the image plane (2). In the case of the lens system shown in FIG. 1 and Table 1, when the movable lens group (2) is moved 0.80886 degrees to the image field side, an image is formed at the image plane (2) (FIG. 3). The focal length of the entire system at this time takes a value from 1.4602 to 11.0991, and the focal length of the zoom lens shown in Figure 1 is 1.460.
The focal length changes within the doubled range.

In addition, the distance between the final surface (33 surfaces) of the lens system and the image plane (back focus) before and after the movement of the movable lens group ■
is unchanged at 2.6742, and the total optical length also does not change.

In the above lens system, the amount of movement of the movable lens group V is D
and the focal length at the wide-angle end by basic zooming is fw
o, If the focal length at the wide-angle end after changing the zoom area is rims, then the zoom area changing magnification R is R=fwe/fwo
It is expressed as In addition, the focal lengths of fixed lens group ■, movable lens group ■, and fixed lens group ■ are fL1, fL2, and f, respectively.
When L3 is assumed, the focal length of the movable lens group V is such that when the movable lens group V is moved by a distance D, images are formed on the same image plane (2). In this case, the back focus also remains unchanged.

FIG. 2 is a diagram showing various aberrations of the zoom lens shown in FIG. 1, in which (A) is at the wide-angle end, (B) is at the intermediate position, and (C) is at the telephoto end.

FIG. 4 is a diagram showing various aberrations of the zoom lens shown in FIG. 3, in which (A) is at the wide-angle end, (B) is at the middle, and (C) is at the telephoto end.

As the movement mechanism for a predetermined movable lens group in the relay lens group in the above embodiment, for example, a mechanism similar to the movement mechanism for the focusing lens group I can be adopted.

Incidentally, instead of the movable lens group V, it may be possible to provide a fixed lens group (2) having a positive refractive power so as to be movable back and forth, but it would not be easy to correct various aberrations.

It is also possible to make the front group of the relay lens group have negative refractive power, the middle group positive, and the rear group positive refractive power, and move the front group with negative refractive power back and forth, but the entire lens system It cannot be adopted because it is too large.

Various preferred embodiments of the present invention have been described above, but
It goes without saying that the present invention is not limited to the embodiments described above, and that many modifications can be made without departing from the spirit of the invention.

(Effects of the Invention) As described above, the zoom lens according to the present invention has positive, negative,
By simply moving the movable lens group with negative refractive power of the relay lens group consisting of three groups with positive refractive power between two positions along the optical axis, the image plane position remains unchanged.
The zoom area can be changed instantly between two areas, providing excellent operability. Further, aberrations can be easily corrected, high performance is achieved, and the structure is simple, so there are few failures and it can be provided at low cost.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a lens cross section at the wide-angle end in the basic state before the movable lens group moves in an embodiment of the zoom lens according to the present invention, and FIGS. )
are diagrams showing various aberrations at each position of the zoom lens shown in Figure 1, and Figure 3 is a diagram showing the aberrations of the zoom lens shown in Figure 1 at the wide-angle end after moving the movable lens group and changing the focal length by zooming. A diagram showing a cross section of the lens, Fig. 4 (A
), (B), and (C) are diagrams showing various aberrations at each position of the zoom lens shown in FIG. 3, respectively. I... Force single lens group, ■, ■... Zooming lens group, ■... Fixed lens group, ■... Movable lens group, ■...
... Fixed lens group, ■... Image plane position. lmt. t line drawing aberration sphere aberration astigmatism distortion self-convergence t1: surface aberration spherical aberration astigmatism well-point aberration cup aberration distortion convergence

Claims (1)

[Claims] 1. A zoom lens having a focusing lens group, a zooming lens group, and a relay lens group from the object world side, wherein the relay lens group has a refractive power that is positive, negative, and positive from the object world side. Among the three lens groups, the lens group with negative refractive power is provided in a movable lens group that can move on the optical axis between two positions that are the same image plane position. A zoom lens characterized by: