JPS59137917A - Zoom lens - Google Patents

Abstract

PURPOSE:To correct thoroughly the change in focus by the effect of temp. and humidity by providing means for detecting temp. and humidity and generating the signal corresponding thereto and means for changing the relative positions of a lens and an imaging plane having a specified rate of contribution to a change in the position of an image plane by zooming. CONSTITUTION:The relative position of the 4th lens group 4 and an imaging plane 5 is changed according to a change in temp. and humidity, by which the change in focus owing to a change in the temp. and humidity is corrected. More specifically, a mechanism 6 for detecting temp. and humidity is provided in such a zoom lens which includes a lens made of said materials in the 4th lens group which is an imaging lens system stationary during zooming. The data thereof is inputted to a mechanism for calculating the rate of correcting the focus by temp. and humidity, where the extent to move the group 4 in order to correct the change in the focus owing to the temp. and humidity is calculated and is inputted to a mechanism 8 for driving a focus correcting member which drives the group 4 so as to move the same by the calculated extent of the movement. A known digital temp. and humidity meter is usable for the mechanism 6 and the extent of the movement for the purpose of focus correction can be calculated by using a microcomputer of a small capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a camera using a zoom lens, particularly a zoom lens that includes a part of the imaging lens system that includes a material whose refractive index or shape changes significantly due to changes in temperature or humidity. It's about cameras.

In recent years, lenses made of materials such as synthetic resins have often been incorporated into lens systems in order to reduce costs, reduce weight, and improve optical performance due to aspherical surfaces. However, lenses made of such materials are subject to temperature and
Its refractive index and shape change greatly depending on humidity, and this change in refractive index and shape affects the focus of the lens system.

In the past, lenses containing such materials had large changes in focus due to temperature and humidity, so they were only put to practical use as short, dark, single lenses. Also, zoom lenses containing this type of material are known for use in projectors, such as those disclosed in U.S. Pat. No. 3,920,315 and U.S. Pat. Since it is necessary to readjust the focus at the camera, changes in focus due to temperature and humidity were not a problem in the first place.

Furthermore, Japanese Patent Application Laid-Open No. 55-143518 discloses a lens that uses a combination of the above-mentioned materials and a paraxial arrangement to offset changes in focus due to temperature, but this is a single lens and a zoom lens. It's not about the lens.

Furthermore, an example of a zoom lens is disclosed in JP-A-57-176015, which is constructed by combining an organic glass lens and an inorganic glass lens so that the amount of residual focus change in each lens group almost cancels out each other during zooming. death,
Regarding the imaging system, since a constant amount of change in focus occurs regardless of zooming, correction is performed independently based on the concept disclosed in Japanese Patent Application Laid-open No. 55-143518.

The present invention aims to correct changes in focus due to temperature and humidity in zoom lenses including lenses made of the above-mentioned materials. This is to correct the influence of temperature and humidity on the focus of the zoom lens included in the imaging system, regardless of the zooming position.

The present invention will be explained in detail below.

The present invention is characterized by having at least a variable magnification lens system and an imaging lens system that is fixed during zooming.
In a zoom lens that includes a lens made of a material whose refractive index and shape change greatly depending on humidity, there is a means for detecting temperature and humidity and generating a signal corresponding to the temperature and humidity, and a method for focusing according to temperature and humidity based on the signal from the means. The present invention includes a means for changing the relative position between the lens, which contributes a constant amount to the change in the position of the image plane, and the image plane by zooming so that no change occurs. In a preferred embodiment of the invention, the relative position changed is the relative position of at least some lenses of the imaging lens system and the imaging surface.

The present invention will be explained in detail below.

Figure 1 shows a lens group 1 that is fixed during zooming and movable in the optical axis direction for focusing, a second lens group 2 that is movable in the optical axis direction for zooming, and a focus change due to zooming. A third lens group 3 that is movable in the optical axis direction to correct
, and a fourth lens group 4 which is fixed during zooming and has an imaging function to form an image of the subject on the imaging plane 5. In this zoom lens, if at least a part of the fourth lens group 4 is made of a material that has a large change in refractive index and/or shape due to changes in temperature or humidity (or both), such as synthetic resin, ,temperature·
The position of the image point changes due to changes in humidity. In this case, if 7 focusing is performed to correct this focus change by moving the tube lens group 1, the amount of movement required for correction will differ depending on the focal length, so if you zoom from the state where focusing is performed, the focus position will change. Change again.

Therefore, in one embodiment of the present invention, in order to prevent such a situation from occurring, the fourth
By changing the relative position of the lens group 4 and the imaging surface 5, changes in focus due to changes in temperature and humidity are corrected. That is, in this embodiment, in the zoom lens shown in FIG. 1, the temperature and the The temperature/humidity data obtained from the humidity detection mechanism 6 is input to the temperature/humidity focus correction amount calculation mechanism, and the fourth lens group 4 is moved to correct the focus change due to temperature/humidity with and \. By calculating the amount to be moved and inputting it to the focus correction member drive mechanism 8, the fourth lens group 4 is driven to move by the calculated movement amount.

A known digital temperature/hygrometer can be used as the temperature/humidity detection mechanism 6, and the amount of movement for the above-mentioned focus correction can be calculated using a multi-capacity microcomputer. As the focus correction member drive mechanism 8, a mechanism using a step motor or the like can be used. Except for special purposes, under the conditions in which this type of zoom lens is used, there is a linear relationship between the amount of change in temperature and humidity and the amount of change in focus associated with it, so proportional calculation can be performed by providing the proportionality coefficient in advance. The above-mentioned correction movement amount can be calculated in the following manner.

The above describes an example of a lens type zoom lens in which the first lens group is fixed during zooming and the second and third lens groups are movable for zooming, but other types of zoom lenses can also be used. If the image system is fixed during zooming, exactly the same effect can be obtained.

Furthermore, in the above embodiment, the entire fourth lens group 4 constituting the imaging system was moved for the purpose of correcting changes in focus due to changes in temperature and humidity, but for the same purpose, only a part of it was moved. Alternatively, embodiments in which the imaging plane 5 is moved are also possible. Particularly in the case of a video camera or the like that uses a solid-state image sensor, it is effective to displace the imaging plane 5.

In addition, in the above embodiment, the sensitivity of the position with respect to the focal plane is #1 in the entire zoom range in place of moving the fourth lens group.
Even by moving the compensator at a constant rate, it is possible to compensate for changes in focus caused by changes in temperature and humidity. Furthermore, the present invention is not limited to this, and in the above embodiments, the relative position between the lens group and the image forming surface, which contributes a constant amount to the change in the position of the image surface due to zooming, is set such that the focus does not change due to temperature and humidity. The objects of the present invention can be achieved by configuring the embodiments described above to be modified by simple means.

Furthermore, the present invention is not limited to a type of zoom lens in which focusing is performed by the first lens group as shown in the figure, but also applicable to a type of zoom lens in which focusing is performed by any lens group other than the final imaging system. Means can accomplish exactly the same purpose.

In addition, in the case of a zoom lens built into a camera, temperature and
All or part of the humidity detection mechanism, focus correction amount calculation mechanism, and focus correction member driving mechanism may be provided within the camera body.

If the focus correction member drive mechanism 8 is provided with an external display means for displaying the amount of correction, it is also possible to manually drive the focus correction member driving mechanism 8 by viewing the display means.

As explained above, according to the present invention, it is possible to completely correct changes in focus due to temperature and humidity in a zoom lens in which a material whose refractive index and shape change greatly depending on temperature and humidity is used in an imaging lens system that is fixed during zooming. I can do it.

The present invention is directed to a zoom lens in which a lens made of the above-mentioned materials is used in an imaging lens system that is fixed during zooming, because it can prevent changes in focus due to temperature and humidity.
This is because it is possible to correct changes in focal length due to zooming by correcting displacement at a single location (for example, relative displacement between the imaging lens system and the imaging surface) without having to take into account changes in focal length each time.

4. Brief explanation of the drawings.

The drawings are diagrams showing one embodiment of the present invention.

DESCRIPTION OF SYMBOLS 1... Focusing lens group, 2... Lens group for variable power, 3... Con-inserter lens group, 4... Imaging lens group, 5... Image forming surface, 6...
- Temperature/humidity detection mechanism, 7... Focus correction amount calculation means, 8... Focus correction member drive mechanism.

Claims (1)

[Claims] 1. A lens that has at least a variable power lens system and an imaging lens system that is fixed during zooming, and that the imaging lens system is made of a material whose refractive index and shape change greatly depending on temperature and humidity. In a zoom lens including a means for detecting temperature and humidity and generating a signal corresponding to the detected temperature and humidity, and a means for detecting a change in the position of the image plane by zooming, based on the signal from the means, so that the focus does not change due to temperature and humidity. A zoom lens comprising a lens having a constant amount of contribution and means for changing the relative position of the imaging plane. 2. The zoom lens according to claim 1, wherein the relative position that is changed is the relative position between at least some lenses of the imaging lens system and the imaging surface.