Imaging optical system

Details Imaging optical system Imaging optical system

2000-10-30

2001-09-11

Dudek, James A. (Department: 2871)

Liquid crystal cells, elements and systems

Liquid crystal optical element

Liquid crystal lenses other than for eyewear

C359S672000, C359S673000, C359S721000, C348S065000

Reexamination Certificate

active

06288767

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an imaging optical system having variable focusing function for an imaging lens, more particularly to an imaging optical system for use in an endoscope which is functioning as a variable focusing element and is useful in case of constructing an imaging element required for a compact imaging optical system, such as an endoscope or the like.
2. Related Art Statement
As a conventional imaging optical system for use in an endoscope for an imaging lens or the like having automatic infocusing switching function, there is an imaging optical system described in, for example, Japanese Patent Application Publication No. 35,090/87. This publication discloses that a holding frame of an objective lens mounted within a range of a distal hard portion of the endoscope is so formed as to extend the frame in the longitudinal direction, thereby moving the frame back and forth mechanically in the longitudinal direction by the operation for focusing adjusting at proximal operating section, resulting in a change of a pint position.
In the conventional imaging optical system disclosed in Japanese Patent Application Opened No. 46,423/90, the imaging optical system comprises a mechanism for selecting polarizing directions and a variable focusing lens utilizing an electro-optical effect of a liquid crystal, thereby changing the focal length of the objective lens by an electrical drive.
The above conventional imaging optical system disclosed in Japanese Patent Application Publication No. 35,090/87, discloses that the mechanism for moving the holding frame mechanically is accommodated in a minimum space, such as a distal hard section for the endoscope, but it is substantially impossible to obtain such a construction due to the spatial restriction.
The above conventional imaging optical system disclosed in Japanese Patent Application Publication No. 46,423/90, has a requirement of a function for selecting the polarizing directions in order to prevent double images from being generated due to the birefringent of the liquid crystal, so that transmittance of the vari-focus lens becomes decreased to 50% or less. Such a decrease of light quantity becomes fatal to the lens for an endoscope, so that usually, as a countermeasure, the diameter of an aperture diaphragm is increased or the diameter of light guide is increased. The former, however, has a defect that the focal depth becomes shallow, and the later has a defect in that as the diameter of the endoscope itself increases. Therefore, both countermeasures are not practical to accommodate such variable focusing function in the endoscope.
SUMMARY OF THE INVENTION
It is an object of the present invention to eliminate the above described disadvantages of the conventional imaging optical system.
It is another object of the present invention to provide a minimized and space saved imaging optical system for use in such as an endoscope, which has a variable focusing function with about a 100% transmitting factor in the far point infocusing condition and in the near point infocusing condition without an accompanying decrease of light quantity, thereby improving the depth of focus and brightness, and thus, obtaining the possibility of magnified observation.
According to a first aspect of the present invention, there is provided an imaging optical system comprising an optical member including a first body consisting of a substantially transparent birefringent liquid crystal member, a second body consisting of a substantially transparent birefringent liquid crystal member, and at least a pair of electrodes for adding an electric field or a magnetic field onto the first body and the second body, a rear face of the first body being aligned perpendicular to a front face of the second body, and the first body and the second body having substantially symmetrical shape against a plane perpendicular to an optical axis.
According to the present invention, the imaging optical system comprises an optical member including a first body consisting of a substantially transparent birefringent liquid crystal member, a second body consisting of a substantially transparent birefringent liquid crystal member, and at least a pair of electrodes for adding an electric field or a magnetic field onto whole the first body and the second body, a rear face of the first body being aligned perpendicular to a front face of the second body, so that if such an imaging optical system is loaded as an imaging optical system for an endoscope, a variable focusing function can be added to the endoscope without any requiring a polarizing plate.
That is, according to the present invention, in the condition that a voltage is not applied to the member, an incident light having a polarizing direction perpendicular to a major axis direction of the liquid crystal at an incident end of the first liquid crystal body is subjected to an effect due to ordinary ray refractive index of the liquid crystal in the first body, and is subjected to an effect due to extraordinary ray refractive index in the second liquid crystal body, in which the major axis direction of the liquid crystal at the incident end is orthogonal to the major axis direction of the liquid crystal at the emerging end of the first body. Moreover, an incident light having a polarizing direction parallel to a major axis direction of the liquid crystal of the first liquid crystal body is subjected to an effect due to extraordinary ray refractive index of the liquid crystal in the first body, and is subjected to an effect due to ordinary ray refractive index in the second liquid crystal body, in which the major axis direction of the liquid crystal is orthogonal to the major axis direction of the first body. In this case, if the first body and the second body are substantially of the same construction, the difference of focus positions due to the polarizing direction becomes a negligible amount. While in the voltage applying condition, the liquid crystal molecular structure is aligned parallel to the optical axis, so that whole incident light flux are subjected to an effect due to ordinary ray refractive index of the liquid crystal and transmitted through the first body and the second body.
The above constructed imaging optical system according to the present invention does not require the function of selecting the polarizing directions for preventing generation of a double image, so that it is possible to obtain an endoscope having a variable focusing function with substantially 100% transmittance both in the far point infocusing condition and in near point infocusing condition.
Particularly, in the micro-optical system, such as an endoscope, the focal length of optical system itself is short, and the diameter of light flux is short, so that in order to load the variable focus liquid crystal lens, the thickness of the liquid crystal may be made thin. Therefore, according to the present invention, it is possible to obtain a variable focus lens with high response speed, high contrast and high transmittance. Moreover, the current endoscope requires high operationality, low invasiveness, and high compaction. If the driving system is an electrical system, therefore, it is preferably compacted that the variable focus liquid crystal lens improves responsibility and contrast property, as the objective system is compacted, thereby imposing the variable focusing function to the endoscope or the like.
Then, if the variable focusing lens is loaded on the endoscope, the following constituent factors to obtain the same lens power for whole polarized light without a polarizer and to obtain sufficient lens power variation and the sufficient response speed as an endoscope, are explained hereinafter.
In order to obtain the same lens power for whole polarized light without arising the double image, as described above, the polarized components incident on the first liquid crystal body as extraordinary ray and the polarized components incident on the first liquid crystal body as ordinary ray

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