JPH0629902B2 - Zoom lens having a function of transiting the zoom area - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention inserts an attachment lens into a part of the zoom lens while keeping the image plane position stationary, thereby making it possible to adjust the zoom lens with and without the attachment of the attachment lens. The present invention relates to a zoom lens having a function of changing the focal length range.

Transition of focal length range of zoom lens, for example, focal length range of 10 mm to 100 mm, focal length range of 15 mm to 1
The following methods are well known as methods for transitioning to the 50 mm one.

(I) a method of attaching and detaching an attachment lens between the zoom lens body and the image surface, (II) a method of exchanging a member not involved in focusing and zooming in the zoom lens, a so-called zoom lens relay section, (III) ) A method of attaching / detaching an afocal lens system whose absolute value of angular magnification is not 1 to / from the subject side of the zoom lens body, (IV) A method in which a zoom system is further provided in the relay section of the zoom lens, (V) Zoom lens The method shown in (V) is also called the built-in extender method, in which the attachment lens is attached to or detached from the relay section of the, the transition of the focal length range immobilizes the image plane position. This is a useful means for transitioning the focal length range because it can be performed instantaneously while keeping it as it is and the structure is simple.

This built-in extender system includes (1) a relay lens group consisting of a front lens group and a rear lens group, as shown in JP-A-52-113753, when an attachment lens is inserted between the two groups. A method for moving a group to the object side, (2) JP-A-52-123637, JP-A-52-139450, JP-A-53-
As disclosed in Japanese Patent No. 23645, etc., a method in which a relay lens group is composed of three groups and an attachment lens is inserted between the relay lens groups at appropriate positions, (3) JP-A-54-135546, As shown in Japanese Laid-Open Publication No. 54-137329, the relay lens group is composed of a front group and a rear group,
A method of inserting an attachment lens having a positive power between both lens groups with the front group and the rear group being fixed.
It has been known. Of these, the simplest method is the method shown in (3). Conventionally, the zoom lens related to the method (3) is a type of long back focus lens in which a three-color separation optical system is arranged between the final surface of the zoom lens and the image surface.

An object of the present invention is to provide a zoom lens in which a relay lens portion is formed of a front group and a rear group, and an attachment lens is inserted between both lens groups in a fixed state to shift a focal length range. In order to provide a zoom lens having a back focus of a normal length which is frequently used at present, for example, for the color television camera, an optimum zoom lens for a TV camera using a single image pickup device is provided. It is in.

A further object of the present invention is to provide a zoom lens which can shorten the back focus and can also downsize the relay lens group.

In the zoom lens according to the present invention, a lens group having a focusing function and a zooming function in order from the object side, and a relay lens group including a front group and a rear group that are stationary during focusing and zooming. In the zoom lens that shifts the focal range by zooming by inserting an attachment lens between the front group and the rear group in a state where the front group and the rear group are fixed, The refracting power of the instrument lens is negative,
The position of the image plane side main plane of the front group is closer to the object field than the position of the object plane side main plane of the attachment lens, and the position of the rear surface side of the object side main plane is the attachment. The back focus is shortened and the relay lens group is downsized by configuring the lens so that it is closer to the object side than the position of the image plane side main plane of the lens.

FIG. 1 shows an embodiment of a thin structure of a zoom lens according to the present invention, and FIG. 1 (A) is a view when an attachment lens is not inserted. A relay lens group including a lens group 11 having a variable magnification function, a front group 12 and a rear group 13 is arranged. The lens group 11
Any specific configuration may be used as long as it can always form an image of an object by the lens group 11 at the same place. In this state, the light flux from the object (not shown) is imaged on the image plane 14. FIG. 1 (B) is a diagram when the attachment lens 15 is inserted. Even when the attachment lens 15 is inserted, the light flux from the object forms an image on the stationary image surface 14, but when the attachment lens 15 is inserted, the image plane side main plane of the front group 12 is formed. By setting the lens system so that the position of 12b is closer to the object side than the position of the object side main plane 15a of the attachment lens 15, the back focus is made shorter than the conventional built-in extender type zoom lens. . In the configuration shown in FIG. 1, the position of the object-side main plane 13a of the rear group 13 is located closer to the image field than the position of the image-side main plane 15b of the attachment lens 15, but By arranging the position of the object-side main plane 13a on the object-side side of the image-side main plane of the attachment lens 15, the relay lens group can be downsized. A description of this area will be given with reference to FIG. 7 showing the relationship between the principal point intervals in the related art and FIG. 8 showing the relationship between the principal point intervals of the present invention. Incidentally, FIG. 7 is a diagram showing a conventional general principal point interval and rays passing through the principal point, showing a long back focus state, and FIG. FIG. 8 (B) shows a state diagram focused on, and FIG. 8 (B) shows a state diagram focused on the image plane side principal plane of the attachment lens.

The light passing through the object-plane-side main plane and the image-field-side main plane has a relationship of exiting from the image-field-side main plane at the same height as when entering the object-plane-side main plane. Therefore, the light flux emitted from the front group 12 is in a convergent state, and the object-side main plane 15a of the attachment lens is
In the zoom lens like the conventional example shown in FIG. 7 in which the lens is on the front side, it passes through the object side main plane 15b of the attachment lens, which is higher than the front lens group 12. Since the image plane side main plane 15b is emitted in a diverging state from this same height, if the refracting power of the rear group 13 is the same as that in FIG. 8, the back focus tends to become longer as is clear from the figure. .

On the other hand, in the case of the zoom lens of the present invention, FIG.
As shown in (A), since the rear group 13 passes through the object-side main plane 15a at a low position, the back focus can be shortened even if the rear group 13 has the same refracting power as in FIG.

On the other hand, as shown in FIG. 8 (B), by disposing the image field side main plane 15b of the attachment lens on the image field side of the image field side main plane 13b of the rear group 13, each main plane (13a, 13a, 13b)
The back focus can be shortened and the relay lens group can be made small by allowing light to pass through the low position.

In this way, even if the attachment lens is inserted, the image plane 14
In order not to change the position of, the following formula is satisfied as in the conventional extender system. _A = alpha / _{[fz, -E 10, R1, -E} 2 ] [-
E _{3] mf 0 E 2 = E 20 -PP'} -α / (α R2 -β) E 3 = α / (α R2 -β) α = S F0 - _{[fz, -E 10, R1, (} PP ' -E
₂₀ )] mf β = 1− [ _fz , −E ₁₀ , _R1 , (PP′−
E ₂₀ ), _R2 ] mf where _fz ; Refractive power of the lens group, which is arranged closer to the object field than the relay group and has the focusing function and the variable power function, _R1 ; Refractive power of the front group of relays, _A ; Attachment lens _{power, R2} of; the refractive power of the rear group relays, _{E 10;} principal point distance between the lens groups 11 a front group 12, _{E 20;} principal point distance between the rear group 13 with the front group 12, _{S F0;} rear group 13 is a distance between the image plane side principal plane 13b and the image forming surface 14, E ₂ is a principal point distance between the front lens group 12 and the attachment lens 15, and E ₃ is a main distance between the attachment lens 15 and the rear lens group 13. Point spacing, PP '; spacing between the principal planes 15a and 15b of the attachment lens 15, f: focal length of the entire system.

FIG. 2 is a diagram showing the position of the principal plane in an embodiment of the attachment lens used in the zoom lens of the present invention. The position of the principal plane of the attachment lens 15 is projected to the image field side, and the object plane side principal plane 15a (front side principal plane)
Is positioned closer to the image field side than the position of the image field side main plane 15b (rear side main plane), so that the object field side main plane 15a is formed as close to the image field side as possible.

Specific examples will be described below. FIG. 3 is a lens cross-sectional view showing an embodiment of the zoom lens according to the present invention, and is a view showing a state when the attachment lens is not attached. The zoom lens is a focusing group I that is movable for focusing from the object side to the image side, a zooming lens group (II, III) that is movable for zooming, and a relay lens group that is fixed during focusing and zooming. Front group IV, also the rear group of relay lenses
VIs are arranged sequentially. VII indicates an image plane. In this system, as the lens groups (II, III) move, the focusing distance changes from 11.2600 to 66.9956. Table 1 shows the lens data. Ri is the radius of curvature of the i-th surface, Di is the i-th surface
Axial thickness or axial air gap between the surface and the (i + 1) th surface, v
Represents the dispersion value, and N represents the refractive index (d line). Incidentally, Fig. 4
(A), (B), (C) are diagrams showing various aberrations of the zoom lens shown in FIG. 3, (A) at the wide-angle end, (B) at the middle, and (C) at the telephoto end. It is a figure of a case.

FIG. 5 is a view showing a lens cross section when the attachment lens V is inserted. When the attachment lens V is attached, the focal length takes a value between 18.410 and 109.539, and the focal length range of the zoom lens shown in FIG. 3 is 1.635.
The focal length changes in the doubled range. Aberration diagrams of the zoom lens shown in FIG. 5 are shown in FIGS. 6 (A), (B) and (C). (A)
FIG. 4A is a diagram showing aberrations at the wide-angle end, FIG.

Next, the focal length of each group of the lens system shown in FIG. 5 and the principal point spacing within the relay lens group are shown in a third display.

As can be seen from Table 3, the refractive power of the attachment lens V is negative, and the position of the image plane side main plane of the lens group IV is closer to the object plane side than the position of the object plane side main plane of the lens group V. Further, it can be seen that the position of the image plane side main plane of the lens group V is closer to the image field side than the position of the object plane side main plane of the lens group VI.

It should be noted that the final surface R of the lens system can be used even when the attachment lens is inserted or removed.
The distance between 27 and image plane VII (back focus) is always 3.1.
Take a value as short as 8 mm.

[Brief description of drawings]

1 (A) and 1 (B) are views for explaining a zoom lens according to the present invention, and FIG. 2 is a view for explaining an example of an attachment lens used in the zoom lens according to the present invention. FIG. 4 is a diagram showing a lens cross section when an attachment lens is not attached, in an embodiment of the zoom lens according to the present invention, FIG.
(B) and (C) are diagrams showing various aberrations at each zoom position of the zoom lens shown in FIG. 3, respectively, and FIG. 5 is a diagram when an attachment lens is attached to the zoom lens shown in FIG. 6 (A), 6 (B), and 6 (C) are views showing various lens aberrations at each zoom position of the zoom lens shown in FIG. 5, respectively. FIG. 7 is a diagram showing a general principal plane relationship in a conventional zoom lens. 8 (A) and 8 (B) are views showing the relationship of the principal planes according to the present invention. Reference numeral 11 ... Lens group having focusing and zooming functions, 12 ... Relay section front group, 13 ... Relay section rear group, 14 ... Image plane, 15 ... Attachment lens, 12b, 13a, 15a, 15b ... Main plane.

Claims (1)

[Claims] 1. A lens group having a focusing function and a zooming function in order from the object side, and a relay lens group that is stationary during focusing and zooming and includes a front group and a rear group. In a zoom lens that shifts the focal range by zooming by inserting an attachment lens between the front group and the rear group while the group and the rear group are fixed, the refractive power of the attachment lens is negative. The position of the image plane side main plane of the front group is closer to the object field than the position of the object plane side main plane of the attachment lens, and the position of the object side main plane of the rear group is the image of the attachment lens. A zoom lens having a function of transiting a zoom region, which is located on the object side from the position of the field-side main plane.