JPH08110459A - Zoom pan focus lens - Google Patents

Abstract

PURPOSE: To secure focus at infinity over the entire focal distance range of zooming and to secure the shortest photographing distance (MOD) at a telephoto end and a wide end to be a short distance by forming a cam groove so as to shift the focus set distance of a zoom intermediate range to the side of the infinity. CONSTITUTION: The top end parts of cam follower members 208 and 408 respectively formed at holding frames 20 and 40 are guided in the direction of an optical axis by the cam grooves 304 and 304 at the inside of the guide groove 14 of a barrel body 10, so that Ath lens system 202 and Bth lens system 402 are moved in the direction of the optical axis keeping a specified relation. The focus set point of the intermediate range of the focal distance is shifted and set on the side of the infinity. Thus, the cam curve grooves 304 and 302 of a cam barrel 30 are formed so as to arrange the Ath lens system 202 and the Bth lens system 402 in order to realize focus set. Also, the depth end on the side of the infinity copes with the infinity and the MOD is set to be the shortest, so that a mechanical error is prevented by fine adjustment at the time of assembling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom pan focus lens for cameras, video cameras and the like, and more particularly to the focus setting of the zoom pan focus lens.

[0002]

2. Description of the Related Art Conventionally widely known zoom lenses are
Equipped with two moving lens groups, a zoom lens and a correction lens,
It is a two-group moving type that moves these moving lens groups in the optical axis direction. FIG. 3 shows the overall configuration of a lens barrel of a general zoom lens, which includes a barrel 10, variator lens holding frames 20, 40, a cam barrel 30, and a compensator lens holding frame 50. In FIG. 1, the compensator lens 12 is mounted on the right end of the cylindrical body 10, and three linear guide grooves 14, 14, 14 are formed in the cylindrical body 10 in the optical axis direction. Three cam followers 208, 208, 20 are provided on the outer peripheral surfaces of the holding frames 29, 40 for holding the variator lenses 202, 402 corresponding to the three guide grooves 14, respectively.
8, 408, 408 and 408 are provided in a protruding manner. Further, in the circumferential direction of the cam barrel 30, there are three cam grooves 302, 302, 302, 304, 304, 304 for guiding the cam followers 208, 408 provided on the outer peripheral surfaces of the holding frames 20, 40.
It is formed in the place. The holding frame 50 holds the compensator lens 502, and the male screw 50 is attached to the right end of the holding frame 50.
4 is formed, and the holding frame 50 is screwed into the female screw 16 formed at the left end portion of the tubular body 10.

With the cam followers 208, 408 of the holding frames 20, 40 fitted in the cam grooves 302, 304 of the cam barrel 30, the cam followers 208, 408 are fitted into the guide grooves 14 of the barrel 10. Meanwhile, the cylinder 10 is inserted between the holding frame 20 and the cam cylinder 30, and then the male screw 504 of the holding frame 50 is screwed into the female screw portion 16 of the cylinder 10 to assemble.

When the cam barrel 30 is rotated in the circumferential direction, the cam followers 20 formed on the holding frames 20 and 40, respectively.
8 and 408 are guided in the optical axis direction by the cam grooves 304 and 304 in the guide groove 14 of the cylindrical body 10, the lenses 202 and 402 are moved in the optical axis direction, and the focal length of the entire lens system is increased. Can be changed. As an application of the above zoom lens mechanism, for example, Japanese Patent Laid-Open No. 63-2
6642 discloses a lens barrel for a video camera, and Japanese Patent Laid-Open No. 02-146532 discloses a zoom lens including a plurality of lens groups in which a field of view from a predetermined short distance to a predetermined long distance or infinity A zoom lens camera that sets a focal position of a zoom lens so as to have a depth is disclosed.

Normally, the pan-focus lens determines the focus setting distance so as to enter the depth of field from infinity to the vicinity in order to sharply focus a deep object from a near view to a distant view. It is inevitable that an error will occur. In order to avoid that it becomes impossible to secure the focus at infinity due to this adjustment error, the adjustment point is adjusted in advance to allow for an error.

The zoom pan focus lens has a focus setting as shown in FIG. 4 in order to ensure infinity and to shorten the shortest shooting distance (MOD) as much as possible. In this case, since the depth end on the infinity side coincides with infinity by design, the MOD can be minimized. In addition, the tele end of the zoom and the wide end
For both ends, ± 10 can be made by fine adjustment during assembly.
Since it is possible to drive up to an error of approximately 15 μm, it is possible to actually secure infinity focus and MOD.

[0007]

However, in the zoom pan focus lens in which the focus is set as shown in FIG. 4, a variation in the actual focus position occurs due to a mechanical error in the zoom cam or the like in the zoom intermediate range. . This is because the focus in the intermediate zoom range cannot be finely adjusted, and securing the focus depends on the mechanical accuracy of the cam groove formed on the cam barrel and the cam follower (cam pin). Normally, the machining accuracy of the cam groove is about ± 25 μm, which is larger than the adjustment error of ± 10 to 15 μm at the tele end and wide end, and the adjustment to correct the error at the time of assembly such as the tele end and the wide end. I can't do it. Therefore, in the intermediate zoom range, the focus position varies due to a mechanical error of the zoom cam or the like. When the focus position shifts to the short-distance side, the depth end on the infinity side shifts to the short-distance side as shown in FIG. 5, and it becomes impossible to secure the infinity focus.

For the purpose of avoiding the above-mentioned inconvenience, if the adjustment point at the telephoto end or the wide-angle end is further shifted in consideration of an error in the intermediate zoom range, the shortest photographing distance at the telephoto end and the wide-angle end becomes long. As a result, the utility value of the pan focus lens is reduced. Further, the zoom lens camera disclosed in Japanese Patent Laid-Open No. 02-146532 only mentions that each focus has a structure in which the distance from the short distance to the long distance falls within the depth of focus, and mechanical error is taken into consideration. There is no description about focus setting.

The present invention has been made in view of such circumstances, and secures an infinite focus over the entire focal length range of the zoom, and also has a shortest shooting distance (MOD) at the tele end and the wide end. An object of the present invention is to provide a zoom pan focus lens that can be secured at a short distance.

[0010]

In order to achieve the above object, the present invention provides a zoom lens including a plurality of lenses, a plurality of lens holding frames to which the lenses are attached, and an outer peripheral surface of the frame. A zoom pan focus lens having a cam barrel formed with a cam follower fitted to protrude from the cam barrel and having a cam groove for advancing and retracting the plurality of frames in the optical axis direction in a predetermined relationship. It is characterized in that the cam groove is formed so as to shift the focus setting distance in the intermediate region to the infinity side.

[0011]

According to the present invention, the set distance of the focus position is set to be shifted to the infinity side only in the zoom intermediate region where a mechanical error of the zoom cam or the like occurs, and the cam curve groove is formed so as to realize this. Form. As a result, even if the focus position of the zoom intermediate region is shifted to the short distance side due to the mechanical error of the cam, it is possible to secure the focus at infinity.

[0012]

The preferred embodiments of the zoom pan focus lens according to the present invention will be described in detail below with reference to the accompanying drawings. Generally, a zoom lens is composed of a zoom system that moves a part of the lens system to change the focal length and a correction system that corrects a focus shift caused by the motion of the zoom system. .

FIG. 1 schematically shows the construction of a zoom pan focus lens according to the present invention. The first group lens system A is a concave lens system in which a focusing system and a variable power system which play the role of a concave lens as a whole are integrated. And the second lens group B
Is a correction system that functions as a convex lens that moves according to the movement of the first group to correct the focus shift. Although the lens configuration of FIG. 1 and the lens configuration of the zoom lens of FIG. 3 are not the same, description will be given below with reference to FIG. 3 for convenience. The first group lens system A in FIG. 1 corresponds to the lens 402 in FIG. 1, and the second group lens system B corresponds to the lens 202 in FIG. Hereinafter, the former will be referred to as the A-th lens system, and the latter will be referred to as the B-th lens system.

The tips of the cam followers 208 and 408 formed on the holding frames 20 and 40 are the guide grooves 1 of the tubular body 10.
By being guided in the optical axis direction by the cam grooves 304, 304 in the fourth lens unit 4, the A-th lens system 202 and the B-th lens system 402 are moved in the optical axis direction with a predetermined relationship.
As shown in FIG. 1, on the wide angle side (wide side), the distance between the concave lens system A of the first group and the convex lens system B of the second group is large, and on the telephoto side (tele side), the distance is small, and they are substantially integrated. hand,
A convex lens system having a focal length longer than that of the second lens unit alone is formed.

FIG. 2 shows the focus setting distance and the depth of field of the zoom pan focus lens according to the present invention.
The focus setting point in the middle range of the focal length is set by shifting to the infinity side, and the depth of field shown by the diagonal lines is shifting to the infinity side. In order to realize the above focus setting, the cam curved grooves 304 and 302 of the cam barrel 30 are formed so that the A-th lens system 202 and the B-th lens system 402 are arranged in FIG. At both the tele end and the wide end of the focal length, the depth end on the infinity side is set to infinity, the MOD is set to be the shortest, and mechanical error is driven by fine adjustment during assembly.

In the zoom pan focus lens constructed as described above, at the telephoto end and the wide-angle end, infinity focus and MOD are ensured by fine adjustment at the time of assembly, and the focus set point in the intermediate zoom range is set. , Fig. 2
As shown in (1), since the distance is set to the infinity side, the entire depth of field (hatched portion in FIG. 2) is shifted to the infinity side. Therefore, even if the focus position in the zoom intermediate region shifts to the short distance side due to a mechanical error of the zoom cam or the like, the depth of field covers infinity and the infinity focus is always secured.

By shifting the focus setting distance in the zoom intermediate region to the infinity side, the MOD in the intermediate region is slightly increased, but there is no inconvenience in use. For example, in the zoom pan focus lens set as shown in FIG.
It is possible to adjust D to about 0.5 m and the MOD at the tele end to about 1.5 m, and the MOD in the middle range is secured in this range.

[0018]

As described above, according to the zoom pan focus lens of the present invention, by shifting the focus setting distance in the zoom intermediate range to the infinity side, the MOD in the intermediate range becomes long. Even if the focus position varies due to a mechanical error of the zoom cam or the like, the focus at infinity can always be secured. Further, for the telephoto end and the wide-angle end, the focus and MOD at infinity are secured by fine adjustment during assembly.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a zoom pan focus lens according to an embodiment of the present invention and optical axis direction displacements of a first group concave lens system and a second group convex lens system.

FIG. 2 is a graph showing a focus setting distance and a depth of field of the zoom pan focus lens according to the present invention.

FIG. 3 is an exploded perspective view showing an example of a conventional zoom lens barrel.

FIG. 4 is a graph showing focus setting distance and depth of field of a conventional zoom pan focus lens.

FIG. 5 is a graph showing the depth of field when the focus position is displaced toward the short distance side due to a mechanical error of the zoom cam or the like in the setting of FIG.

[Explanation of symbols]

 10 ... Cylindrical body 20, 40, 50 ... Lens holding frame 30 ... Cam barrel 208, 408 ... Cam follower (cam pin) 302, 304 ... Cam groove A ... First group concave lens system B ... Second group convex lens system

Claims (1)

[Claims] 1. A zoom lens comprising a plurality of lenses, a plurality of lens holding frames to which the lenses are attached, and cam followers protruding from an outer peripheral surface of the frames are fitted to the plurality of frames. In a zoom pan focus lens equipped with a cam barrel formed with a cam groove for moving the body forward and backward in a predetermined relationship, the focus setting distance in the middle zoom range is shifted to the infinity side. A zoom pan focus lens, wherein the cam groove is formed.