JPH04253042A - Shift zoom lens system - Google Patents

Abstract

PURPOSE:To obtain the shift zoom lens system which enables swing and tilt photography through a zoom lens and prevents the center of a subject image from moving to the center of an image formation plane even in zooming operation. CONSTITUTION:In the zoom lens wherein >=2 lens groups S and V are moved at the time of the zooming, the whole or part of the lens group S in front of the lens group V having a power varying function can be shifted about the main optical axis X (at right angles to the main optical axis).

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens used in cameras and the like, and more particularly to a shift zoom lens system capable of focusing on a subject plane whose center is displaced with respect to the principal optical axis.

0002

2. Description of the Related Art Conventionally, when photographing with a camera or the like, tilt photographing is performed in order to focus on an object whose center is displaced with respect to the main optical axis. In order to perform this tilt photography, the principal point of the lens system may be positioned on a line connecting the center of the subject plane and the center of the imaging plane. Therefore, in a normal camera, the shooting film plane is fixed relative to the camera body, so the lens system is aligned perpendicular to the principal optical axis (the optical axis that passes through the center of the imaging plane and is perpendicular to the imaging plane). configured to displace (shift),
This shift amount may be adjusted.

0003

[Problems to be Solved by the Invention] However, if the entire lens system is simply configured to be shiftable, the mechanism for shifting the lens system tends to be large, especially when used for this type of tilt photography. Wide-angle lenses are often constructed from lenses with relatively large diameters, which increases the weight of the lens system and increases the size of the shifting mechanism. Therefore, when installing this type of shift mechanism in a zoom lens, in addition to the mechanism for moving the variable power lens group that performs zooming, the entire lens system including this variable power lens group must be shifted. However, it is extremely difficult to apply such a configuration to a camera lens or the like in order to reduce the size and weight of the camera. or,
If a configuration in which the lens is simply shifted is adopted, the center of the subject image to be photographed may be moved with respect to the center of the image plane due to zooming.

[0004] An object of the present invention is to provide a shift zoom lens system that allows tilting photography with a zoom lens. Another object of the present invention is to provide a shift zoom lens system in which the center of a subject image does not move with respect to the center of the image plane even during zooming.

[0005]

[Means for Solving the Problems] The tilt zoom lens system of the present invention is a zoom lens in which at least two or more lens groups are moved during zooming, in which the entire lens group in front of the lens group having a variable power function is provided. Or a part thereof is configured to be shiftable with respect to the main optical axis.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. FIG. 1 is a diagram for explaining the basic concept of the present invention using a thin lens system, and FIG. 1(a) shows the short focus side, and FIG. 1(b) shows the long focus side. In these figures, O is an object, FP is an imaging plane of a lens system in which photographic film, etc. in a camera is placed, and ZL is a zoom lens system. This zoom lens system ZL is composed of two groups,
The first lens group is used as a shift group S and is configured to be shiftable in a direction perpendicular to the principal optical axis X of the zoom lens system ZL. Further, the second lens group is configured as a variable power group V so as to be movable in the front-rear direction along the main optical axis X. By this movement of the variable power group V, the shift group S is also moved along the principal optical axis X, thereby changing the focal length of the entire zoom lens system ZL to perform zooming.

When the center C of the object O is displaced by a height H with respect to the principal optical axis X, the shift group S is shifted by δ with respect to the principal optical axis X to bring the image IS to the focal point FS. Form an image. At this time, the center of the image IS is positioned on the main optical axis X by adjusting the shift amount δ. In other words, the height H is H=
The relationship is δ/mA. mS is the lateral magnification of the shift group S, and when the distance to the object O is sufficiently larger than the focal length fS of the shift group S, the shift group S is slightly closer to the main optical axis
Even when moving along , the lateral magnification mS remains approximately constant. As a result, H remains constant as long as the shift amount δ of the shift group S is kept constant. Therefore, when this image IS is focused on the imaging plane FP as the subject image I by the variable magnification group V, the center of the subject image I is aligned with the center position of the imaging plane FP. This imaging position is maintained even when the variable magnification group V and accompanying shift group S are moved on the principal optical axis X, so the image will not be moved on the imaging plane even when zooming. There isn't.

Incidentally, as shown in FIGS. 2A and 2B, conceptual diagrams of the short focus side and long focus side when the variable power group V is shifted, respectively, the variable power group V is shifted. Sometimes, the height H of the object O becomes H=δ'/mS=(1-1/mV)δ/mS. Here, mS=δ'/H, mV=δ/(δ-δ'). In addition, δS' and δL' are the heights of the center of the image IS on the principal optical axis when the variable power group V is shifted by the shift amount δ at short focus and long focus, respectively, and HS and HL are the subject at that time. This is the height of the center C with respect to the main optical axis X of O. Therefore, since mV=f/fS, mV changes significantly during zooming. Therefore, when zooming is performed by moving the variable magnification group V while keeping the shift amount δ of the variable magnification group V constant, the height H of the center of the object O is changed. This means that the subject image I formed on the imaging plane FP is moved by zooming.

FIG. 3 is a schematic diagram of a second embodiment of the present invention, in which the first lens group constituting the zoom lens system ZL is composed of a plurality of lens groups. Figure (b)
indicates the long focal point side, and each indicates a thin lens system. In this embodiment, the first lens group is composed of a fixed group A and a shift group S, and by shifting only the shift group S, the camera performs defocus photography, and the second lens group is used as a variable power group V to provide the main light. Zooming is performed by moving on the axis X. In this zoom lens system ZL, the object image I is shifted to the center position of the imaging plane FP by shifting the shift group S, which is a part of the first lens group disposed in front of the variable magnification group V. The subject image I can be kept in focus even when zooming is performed using the variable magnification group V.

In this case, the height H of the center C of the object O is expressed as H=(1-1/mS)δ/mA. mS is the lateral magnification of the shift group S, mA is the lateral magnification of the fixed group A, and when the distance to the subject O is larger than the focal length of the shift group S and fixed group A, the lateral magnifications mS and mA are respectively is substantially constant, and therefore the height is also substantially constant, and the subject image I is not moved on the imaging plane FP even by zooming by the variable magnification group V.

[0011]

As explained above, in the present invention, the entire front lens group or a part thereof of the lens group having a variable power function is configured to be shiftable with respect to the main optical axis. In addition to making tilt-shift photography possible, the shift mechanism can be made smaller and lighter because there is no need to shift the entire zoom lens. Furthermore, according to the present invention, even during zooming, the in-focus state is maintained and the image does not move.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a thin lens system in a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a thin lens system that is less preferable than the first embodiment.

FIG. 3 is a configuration diagram of a thin lens system in a second embodiment of the present invention.

[Explanation of symbols]

ZL zoom lens system S shift group V variable magnification group X Main optical axis O Subject δ Shift amount I Subject image

Claims (1)

[Claims] Claim 1: In a zoom lens in which at least two or more lens groups are moved during zooming, the entire or part of the front lens group of the lens group having a variable magnification function is moved relative to the main optical axis. A shift zoom lens system characterized by being configured to be shiftable in a direction perpendicular to the axis.