JP3362813B2 - Zoom pan focus lens - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom pan focus lens of a camera, a video camera and the like, and more particularly to a focus setting of a zoom pan focus lens. [0002] Conventionally known zoom lenses are
Equipped with two moving lens groups, a variable power lens and a correction lens,
This is a two-group moving type in which these moving lens groups are moved in the optical axis direction. FIG. 3 shows the entire configuration of a lens barrel of a general zoom lens, and includes a cylinder 10, variator lens holding frames 20, 40, a cam cylinder 30, and a compensator lens holding frame 50. In FIG. 1, a 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, 408 are protruded. In the circumferential direction of the cam cylinder 30, three cam grooves 302, 302, 302, 304, 304, 304 for guiding cam followers 208, 408 projecting from the outer peripheral surfaces of the holding frames 20, 40 are provided.
It is formed in the place. The holding frame 50 holds the compensator lens 502, and the right end of the holding frame 50 has a male screw 50.
4 is formed, and the holding frame 50 is screwed into the female screw 16 formed at the left end of the cylindrical body 10. With the cam followers 208 and 408 of the holding frames 20 and 40 fitted in the cam grooves 302 and 304 of the cam cylinder 30, the cam followers 208 and 408 are fitted into the guide grooves 14 of the cylindrical body 10. The cylindrical body 10 is inserted between the holding frame 20 and the cam cylinder 30 while the male screw 504 of the holding frame 50 is screwed into the female screw portion 16 of the cylindrical body 10. When the cam cylinder 30 is rotated in the circumferential direction, the cam followers 20 formed on the holding frames 20 and 40 respectively.
8, 408 are guided in the optical axis direction by the cam grooves 304, 304 in the guide groove 14 of the cylindrical body 10, the lenses 202, 402 are moved in the optical axis direction, and the focal length of the entire lens system is reduced. Can be changed. For example, Japanese Patent Application Laid-Open No.
No. 6642 discloses a lens barrel for a video camera. Japanese Patent Application Laid-Open No. 02-146532 discloses a zoom lens comprising a plurality of lens groups. A zoom lens camera that sets a focal position of a zoom lens so as to have a depth is disclosed. Normally, a pan focus lens determines the focus setting distance from infinity to near to be within the depth of field in order to sharply focus from a near view to a distant view of a deep subject. It is inevitable that errors will occur. In order to avoid that the focus at infinity cannot be ensured due to the adjustment error, the adjustment is made to an adjustment point that allows for the error in advance. The zoom pan focus lens is set to focus as shown in FIG. 4 in order to secure focus at infinity and to minimize the minimum photographing distance (MOD). 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 (telephoto) end of the zoom and the wide (wide angle)
For both ends, ± 10 due to fine adjustment during assembly.
Since the error can be reduced to about 15 μm, the infinity focus and the MOD can be actually secured. [0007] However, in a zoom pan focus lens in which focus is set as shown in FIG. 4, the middle zoom region varies from the actual focus position due to a mechanical error of a zoom cam or the like. Occurs. This is because the focus in the middle zoom range cannot be finely adjusted, and the assurance of the focus depends on the mechanical accuracy of the cam groove and the cam follower (cam pin) formed in the cam barrel. Normally, the processing accuracy of the cam groove is about ± 25 μm, which is larger than the adjustment error of the tele end and the wide end ± 10 to 15 μm. I can't do that. Therefore, in the middle 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 near distance side, as shown in FIG. 5, the depth end on the infinity side shifts to the near distance side, so that it is impossible to secure the infinity focus. To avoid the above-mentioned inconvenience, if the correction in the telephoto end or the wide end is further shifted by correcting the error in the intermediate zoom range, the shortest photographing distance at both the telephoto end and the wide end becomes longer. As a result, the utility value as a pan focus lens is reduced. Further, the zoom lens camera disclosed in Japanese Patent Application Laid-Open No. 02-146532 only describes that the focal point has a structure that falls within the depth of focus from a short distance to a long distance at each focal point. There is no description about focus setting. The present invention has been made in view of such circumstances, and secures infinity in focus over the entire focal length range of zooming, and also has a minimum shooting distance (MOD) at the telephoto end and the wide end. It is an object of the present invention to provide a zoom pan focus lens that can be secured at a short distance. [0010] SUMMARY OF THE INVENTION The present invention, in order to achieve the object, a plurality of lenses, each lens retaining frame
Is held, Tei projecting from the outer peripheral surface of the lens holding frame
Yes cam follower a mated structure with the cam groove of the cam cylinder that
And rotating the plurality of lenses by rotating the cam barrel.
In a zoom pan focus lens in which the focal length is changed by moving in the optical axis direction with a predetermined relationship defined by the cam groove, the depth of field is at the tele end and the wide end.
Pin so that the depth end on the infinity side of degrees matches infinity
Along with the door set distance is set, with the zoom intermediate range
The end of the depth of field on the infinity side to infinity.
If the focus setting distance is set to a distance further shifted to infinity than the focus setting distance to be set when
The cam groove having such a shape as to realize the setting.
Are formed on the cam cylinder . According to the present invention, the set distance of the focus position is set to be shifted toward infinity only in the middle zoom region where a mechanical error of the zoom cam or the like occurs, and the cam is realized to realize this. Form a curved groove. Thereby, even when the focus position in the middle zoom range shifts to the short distance side due to the mechanical error of the cam, it is possible to secure the focus at infinity. Preferred embodiments of a zoom pan focus lens according to the present invention will be described below in detail with reference to the accompanying drawings. In general, a zoom lens can be roughly divided into a zoom system that moves a part of the lens system to change the focal length and a correction system that corrects the focus shift caused by the movement of the zoom system. . FIG. 1 schematically shows the structure of a zoom pan focus lens according to the present invention. A first lens unit A is a concave lens system in which a focus system and a variable power system play the role of a concave lens as a whole system. And the second lens unit B
Reference numeral denotes a correction system that functions as a convex lens that moves in accordance with the movement of the first lens group and corrects out-of-focus. Although the lens configuration of FIG. 1 and the lens configuration of the zoom lens of FIG. 3 are not the same, they will be described 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 an A-th lens system, and the latter will be referred to as a B-th lens system. The distal ends of the cam followers 208 and 408 formed on the holding frames 20 and 40 respectively correspond to the guide grooves 1 of the cylindrical body 10.
The A-th lens system 202 and the B-th lens system 402 are moved in the optical axis direction in a predetermined relationship by being guided in the optical axis direction by the cam grooves 304, 304 in the inside 4.
As shown in FIG. 1, the distance between the concave lens system A of the first group and the convex lens system B of the second group is large on the wide-angle side (wide side), and the distance is short on the telephoto side (tele side), so that they are substantially integrated. hand,
A convex lens system having a longer focal length than the convex lens system alone of the second group is formed. FIG. 2 shows the focus set 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 to be shifted toward infinity, and the depth of field indicated by oblique lines is shifted toward infinity. In order to realize the focus setting, the cam curved grooves 304 and 302 of the cam cylinder 30 are formed so as to arrange the A-th lens system 202 and the B-th lens system 402 in FIG. In addition, at 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 a mechanical error is driven by fine adjustment at the time of assembly. In the zoom pan focus lens configured as described above, the infinity focus and the MOD are secured at the tele end and the wide end by fine adjustment at the time of assembling. , FIG. 2
As shown in (2), since the setting is shifted to the infinity side, the entire depth of field (the shaded portion in FIG. 2) is shifted to the infinity side. Therefore, even if the focus position in the middle zoom range 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 set distance in the middle zoom range to the infinity side, the MOD in the middle range slightly increases, but there is no inconvenience in use. For example, in a zoom pan focus lens set as shown in FIG.
D can be adjusted to about 0.5 m, and the MOD at the telephoto end can be adjusted to about 1.5 m, and the MOD in the middle range is secured in this range. As described above, according to the zoom pan focus lens according to the present invention, the MOD in the middle range becomes longer by shifting the focus set distance in the middle range to the infinity side. However, even if the focus position fluctuates due to a mechanical error of the zoom cam or the like, the infinity focus can always be secured. At the telephoto end and the wide end, focus and MOD at infinity are secured by fine adjustment at the time of assembly.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing an outline of a zoom pan focus lens according to an embodiment of the present invention and a displacement of a first group concave lens system and a second group convex lens system in the optical axis direction. FIG. 2 is a graph showing a focus set distance and a depth of field of a 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 a focus set distance and a depth of field of a conventional zoom pan focus lens. FIG. 5 is a diagram showing a focus position shifted to a short distance side due to a mechanical error of a zoom cam or the like in the setting of FIG. 10 is a graph showing the depth of field in the case of [Description of reference numerals] 10 ... Cylinders 20, 40, 50 ... Lens holding frame 30 ... Cam cylinders 208, 408 ... Cam followers (cam pins) 302, 304 ... Cam groove A … First group concave lens system B… The second group convex lens system

Claims (1)

(57) [Claims] [Claim 1] A plurality of lenses each having a lens holding frame
Is held, Tei projecting from the outer peripheral surface of the lens holding frame
Yes cam follower a mated structure with the cam groove of the cam cylinder that
And rotating the plurality of lenses by rotating the cam barrel.
In a zoom pan focus lens in which the focal length is changed by moving forward and backward in the optical axis direction with a predetermined relationship determined by the cam groove , the telephoto end and the wide end are on the infinity side of the depth of field.
The focus distance is set so that the depth edge matches infinity.
And the depth of field for the middle zoom range.
Is set when the infinity depth end of
Further shifted to the infinity side than the focus set distance to be
Distance is set to the focus setting distance.
A zoom pan focus lens, wherein the cam groove having a shape to be realized is formed in the cam cylinder .