JPH04253041A - Shift lens system - Google Patents

Abstract

PURPOSE:To obtain the shift lens system which can reduce the size of a shift mechanism and also extends a camera system and reduces the cost by being fitted to an existent master lens system. CONSTITUTION:The rear lens group B of the lens system consisting of the front group A and rear group B is so constituted that the lens group can shift at right angles to the main optical axis X. In this case, the master lens system is composed of the front lens group A and the rear lens group B may be constituted behind this master lens system detachably as an adapter shift lens system. Further, the lateral magnification of the rear lens group is set preferably to >=1.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an optical system used in cameras, etc., and in particular to a shift system for focusing on a subject plane whose center is offset from the center of the imaging plane of photographic film, etc. Regarding lens systems.

0002

2. Description of the Related Art Conventionally, when photographing with a camera or the like, tilt photographing is performed to focus on a subject plane whose center is shifted from the center of an imaging plane. 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). What is necessary is to configure it so that it is displaced (shifted) and adjust the amount of this shift.

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, which makes it particularly difficult to use for this type of tilt photography. Wide-angle lenses with large diameters are often composed of lenses with relatively large diameters, which increases the weight of the lens system and increases the size of the mechanism for shifting. For this reason, a lens system has been proposed in which the lens system is divided into a front group and a rear group, and the front group is shifted while focusing is performed in the rear group. However, the wide-angle lens described above has a large front group. Since lenses with large apertures are arranged, it is difficult to solve the above-mentioned problems. Furthermore, since this type of shift lens is generally constructed as a dedicated lens, it is necessary to prepare it separately from a normal lens, which poses the problem of increasing costs when constructing a camera system.

[0004] An object of the present invention is to provide a shift lens system that allows the shift mechanism to be downsized. Another object of the present invention is to provide a shift lens system that can be attached to an existing master lens system to expand the camera system and reduce costs.

[0005]

[Means for Solving the Problems] The shift lens system of the present invention is capable of shifting the rear lens group of a lens system consisting of a front group and a rear lens group in a direction perpendicular to the principal optical axis. Configure. In this case, the front lens group may constitute a master lens system, and the rear lens group may be configured to be removably attached as an adapter shift lens system behind the master lens system. Further, it is preferable to set the lateral magnification of the rear lens group to be larger than 1.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a lens system for explaining the basic concept of the present invention. In the figure, O is an object, FP is an imaging plane of a photographic film, etc., on which the object O is imaged, and the lens system includes a front group A configured as a master lens system, and a front group A configured as a master lens system. It consists of a rear group B as an adapter shift lens system that is detachably attached to the rear side. Also, the rear group B is the front fixed group B1 here.
, a shift group S, and a rear fixed group B2, and the shift group S is configured to be able to shift in a direction perpendicular to the main optical axis X. The front group A constitutes a combined system with the front fixed group B1 of the rear group B, and its principal point P directs the image IA to the focal point F.
Image is formed on A. In addition, by shifting the shift group S by the shift amount δ, the rear group B moves the image IA to the imaging plane FP.
At this time, the center of the subject image I is positioned on the principal optical axis X, and tilt photography is performed.

Here, let H be the height at which the center C of the object O is displaced with respect to the principal optical axis X, and mAB be the composite lateral magnification of the master lens group A and the front fixed group B1 of the rear group B. If the lateral magnification of the shift group S is mS, the following relationship is obtained: H=(1-1/mS)δ/mAB. In other words, when the height H and the shift amount δ have this relationship, the center of the subject image 1 is made to coincide with the principal optical axis X, and focusing on the subject O is achieved.

Therefore, this shift lens system is configured to shift the entire rear group B of the lens system or only a part of it, so that an object displaced with respect to the main optical axis can be imaged at a predetermined position on the imaging plane. Since tilt photography can be realized, the shift mechanism can be made more compact than when shifting the entire lens system or when shifting the front group of a master lens system with a large aperture. Furthermore, by configuring the rear group B as an adapter shift lens system, the existing master lens system can be used as is to configure the shift lens system, and costs can be reduced when constructing the camera system.

FIG. 2 is a diagram showing an embodiment of the present invention.
An example is shown in which a master lens system consisting of a wide-angle lens with a focal length fA = 15.4 mm is used as the front group A, and a detachable adapter shift lens system is used as the rear group B disposed on the rear side. There is. This adapter shift lens system B is configured to shift as a whole, its lateral magnification mB is mB = 1.735, and the focal length of the entire lens system when this adapter shift lens system is attached. Let f be f=26.7 mm. In this configuration, by shifting the adapter shift lens system by a shift amount δ with respect to the principal optical axis X, the subject image I can be focused on the imaging plane FP based on the relational expression shown in FIG. .

[0010] If there is a restriction on the screen size in the imaging plane, an adapter shift lens system is attached to the master lens system so that the maximum half-field angle of light will not be lost when shifting. Since the maximum half angle of view when shifting cannot be made larger than the half angle of view of the master lens system, it is necessary to make the lateral magnification of the adapter lens system greater than 1. That is, the focal length is increased and the half angle of view is decreased. For example, in this example, if the maximum image height y is 21.6 mm, the half angle of view ωM of the master lens system A is ωM≒55 degrees, and the synthesis when the shift amount δ of the shift lens system is 0 The half angle of view ω0 of the entire lens system becomes ω0≈39 degrees. From this, the maximum value ω of the half angle of view of the composite lens system when shifted is tanω≒(
From the relationship y+(mB-1))δ/mBfA, when δ=5, ω≈44 degrees. Although it is basically possible to shift until it becomes equal to the half angle of view of the master lens system, the amount of shift may be limited depending on the diameter of the adapter. Further, if there is no restriction on the screen size, the horizontal magnification may be smaller than 1.

[0011]

[Effects of the Invention] As explained above, in the present invention, since the rear lens group is configured to be shiftable, the shift mechanism can be downsized even in a wide-angle lens with a large aperture.
The shift lens system can be made lighter and smaller, and it is also possible to easily perform tilt photography by shifting. In addition, by configuring the rear group as an adapter shift lens group, a shift lens system can be configured simply by attaching this rear group to an existing master lens system, making effective use of the existing master lens and expanding the camera system. Cost reduction can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a lens system configuration diagram explaining the basic concept of the present invention.

FIG. 2 is a lens configuration diagram of an embodiment of the present invention.

[Explanation of symbols]

A Front group (master lens system) B Rear group (shift lens system) S shift group X Main optical axis O Subject δ Shift amount H Subject center height

Claims (3)

[Claims] [Claim 1] A lens system comprising a front lens group and a rear lens group, characterized in that the entire rear lens group or a part thereof is configured to be shiftable in a direction perpendicular to the principal optical axis. Shift lens system. 2. The shift lens system according to claim 1, wherein the front lens group constitutes a master lens system, and the rear lens group is configured to be detachably attached as an adapter shift lens system behind the master lens system. . 3. The shift lens system according to claim 1, wherein the lateral magnification of the rear lens group is set to be greater than 1.