JPH034211A - Vari-focal lens - Google Patents

Abstract

PURPOSE:To compensate the on-axis astigmatism and preclude over-compensation and to improve the resolving power by providing a compensating lens which varies in refracting power so that the astigmatism generated by the lens is compensated. CONSTITUTION:This lens consists of a lens 21 made of uniaxial crystalline calcite, a polarizing plate 22 which is arranged opposite the projection side of the lens 21, a liquid crystal cylindrical lens 23 as a compensating lens arranged concentrically with the lens 21 across the polarizing plate 22, and a voltage applying circuit 24 which adjusts the refracting power of the lens 23. Consequently, when a voltage is applied to a liquid crystal layer 34, the orientation state of liquid crystal molecules changes to give the lens 23 refracting power similar to that of a transparent flat plate and when the voltage application is stopped, the lens 23 has refracting power similar to that of a normal cylindrical lens.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a variable focus lens that has a variable focus function by combining a lens made of a material exhibiting uniaxial crystallinity with a linear polarizing plate or the like.

[Conventional technology]

Generally, a lens using an optical material exhibiting uniaxial crystallinity, which is manufactured so that the optical axis of the optical material is perpendicular to the optical axis of the lens system, has two different focal lengths for incident light. is known to show. That is, the refractive index of a material exhibiting uniaxial crystallinity can be expressed as a refractive index ellipsoid having a refractive index No for ordinary rays and a refractive index Ne for extraordinary rays, so the focal length Fo for each refractive index No and Ne is Fe can be calculated using the following formula.

1/Fo - (No-1)/r 1/Fe - (Ne-1)/r Lenses that exhibit different focal lengths Fo and Fe in this way are
By combining it with a linear polarizing plate, it can be used as a variable focus lens. That is, when the above lens made of an optical material exhibiting uniaxial crystallinity is combined with a linear polarizing plate and the linear polarizing plate is rotated, it exhibits two different focal lengths and a single focal length at every 90°.

This type of variable focus lens combines a lens made of a uniaxial crystalline material with a TN liquid crystal element, and is capable of switching between two focal lengths without mechanical movement such as rotating the number of polarization. , a method in which both the lens and the polarization plane rotating element (for example, a rotatable polarizing plate, the above-mentioned TN liquid crystal element, etc.) are manufactured using liquid crystal in order to reduce costs has been proposed in JP-A-54-151854. ing.

In addition, a liquid crystal lens has been developed in which the focal length can be continuously changed by adjusting an externally applied voltage without using a polarization plane rotation element. -32348 Publication, JP-A-54-9965
This is proposed in Publication No. 4, etc.

In the liquid crystal lens disclosed in the above publication, as shown in FIGS. 9 and 10, transparent substrates 1 and 2 are arranged facing each other with a spacer 3 interposed therebetween, and the lens is disposed between the transparent substrates 1 and 2. A liquid crystal layer 4 is formed by sealing a liquid crystal in a space shaped like the shape of a liquid crystal. Further, transparent conductive layers 4 and 5 are formed on the opposing surfaces of the transparent substrates 1 and 2 forming this liquid crystal layer space.
Furthermore, an alignment film 7 is formed on the surfaces of the transparent conductive layers 5 and 6. A voltage application circuit consisting of an AC voltage source 8, a voltage adjustment circuit 9, etc. is connected to each transparent conductive layer 5.6.

By using the liquid crystal lens 10 configured in this way in combination with a polarizing plate 11, as shown in FIG.
When a voltage is applied to the liquid crystal layer 4 from the voltage application circuit, the director of the liquid crystal changes, the apparent refractive power of the liquid crystal for linearly polarized light in a specific direction changes, and as a result, the refractive power of the liquid crystal lens 10 changes. Become something.

Variable focus lenses including liquid crystal lenses have the advantage of being able to perform focusing, which was done by adjusting the distance between lenses in conventional lens systems, with almost no mechanical movement of the lenses. be.

[Problem to be solved by the invention]

However, with conventional variable focus lenses made using materials that exhibit uniaxial crystallinity, when the polarization direction is selected so as to exhibit refractive power for extraordinary rays and light is incident, a focused spot with poor symmetry is created. There was a problem in that the focus accuracy deteriorated due to the occurrence of astigmatism. That is, the first
As shown in Figure 2, when linearly polarized light is incident on a lens 12 made of a material exhibiting uniaxial crystallinity so as to form an extraordinary ray, light passing through point A of the lens 12 and light passing through point AA of the lens 12 are separated. The point AX where these intersect does not match the point BX where the light passing through point B and the light passing through point BB intersect. this is,
Even though the long and short axes of the refractive index ellipsoid and the normal to the lens surface are mechanically conjugate to the optical axis of the lens, there is a difference in the positional relationship. This is caused by putting it away.

Note that when ordinary rays are made to enter the lens 12, the positional relationship between the long and short axes of the refractive index ellipsoid and the normal to the lens surface is mechanically adjusted relative to the optical axis of the lens. Since no difference occurs at conjugate positions, the above problem does not occur.

Therefore, even if the variable focus lens described above is applied to a lens system that requires a higher resolving power than the circle of least confusion due to axial astigmatism when an extraordinary ray is incident, it has the disadvantage that it cannot fully demonstrate its resolving power. .

In addition, in eyeglass lenses, etc., astigmatism is corrected using lindrical lenses and toric lenses, but when applied to the variable focus lens mentioned above, when ordinary rays are incident, , there is a problem that over-correction occurs and a new axial astigmatism occurs.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a variable focus lens that can effectively correct axial astigmatism, prevent overcorrection, and significantly improve resolution.

[Means to solve the problem]

In order to solve the above problems, the present invention combines a lens made of a material exhibiting uniaxial crystallinity with a polarizing means, and corrects astigmatism caused by the lens in a variable focus lens having a variable focus function. The structure includes a correction lens whose refractive power changes as shown in FIG.

Further, the correction lens is constituted by a liquid crystal lens in which a semi-cylindrical liquid crystal layer is formed, and the refractive power thereof is changed by applying a voltage to the liquid crystal layer.

Note that calcite or liquid crystal may be used as the material exhibiting uniaxial crystallinity, and in particular, in the case of a lens using liquid crystal, the structure is provided with an electric voltage application means for applying voltage to the liquid crystal. This is desirable.

Also, as a polarizing means, a rotatable linear polarizing plate is used.

It is desirable to use a polarization plane rotation element using a modified product.

[Effect]

Since the present invention takes the above measures, by changing the refractive power of the correction lens, it is possible to operate the correction lens as, for example, a cylindrical lens capable of correcting astigmatism, and also to have a special refractive power. It can be operated as a transparent flat plate (not shown). therefore,
When astigmatism occurs, for example, it operates as a cylindrical lens, and when no astigmatism occurs, it operates as a transparent flat plate, which can effectively correct astigmatism and prevent over-correction. It can be prevented.

〔Example〕

Examples of the present invention will be described below.

FIG. 1 is a diagram showing the configuration of a variable focus lens according to a first embodiment. This variable focus lens includes a calcite lens 21 made of calcite exhibiting uniaxial crystallinity, and a calcite lens 21 made of calcite that exhibits uniaxial crystallinity.
1, a liquid crystal cylindrical lens 23 serving as a correction lens arranged concentrically with the lens 21 through the polarizing plate 22, and adjusting the refractive power of the liquid crystal cylindrical lens 23. It is composed of a voltage application circuit 24 that performs the following steps.

The calcite lens 21 has an optical axis in the direction of the arrow in the figure. The refractive indices of calcite for ordinary and extraordinary rays are 1.651135 and 1.48640, respectively, when the thickness is 589 nm. Therefore, if the lens 21 is considered to be a thin lens and its focal lengths are calculated, the respective focal lengths are 182.27 mm and 246.71 mm. Therefore, it looks like parallel light is incident! When the polarizing plate 22 is rotated, the two focal lengths are switched every 90 degrees, and at an angle between the two focal lengths, the lens has a double salt point.

As shown in FIG. 2, the liquid crystal cylindrical lens 23 includes a lens substrate 3 whose opposing surface is formed into a semi-cylindrical concave surface.
1 and the flat glass substrate 32 form a rectangular spacer 33.
The lens substrates 31 . A liquid crystal layer 34 is formed between the flat glass substrates 32 by sealing liquid crystal in a semi-cylindrical lens-shaped space.

Liquid crystal layer 34 of lens substrate 31 and flat glass substrate 32
A transparent conductive layer 35 is formed on each of the opposing surfaces forming the transparent conductive layer 35, and an alignment film 36 is further formed on the surface of the transparent conductive layer 35. A voltage application circuit 24 consisting of an AC voltage source, a voltage adjustment circuit, etc. is connected to each transparent conductive layer 35. Note that the switch S1 shown in FIG. 2 is shown in a state in which the applied voltage is cut off by adjusting the voltage adjustment circuit, and the liquid crystal molecules 34a of the liquid crystal layer 34 are homogeneously aligned in the state in which the voltage is cut off. Further, as shown in FIGS. 4 and 5, when a voltage is applied, the directors of the liquid crystal molecules 34a rotate and are oriented in the vertical direction in the figures.

In the liquid crystal cylindrical lens 23 configured in this way, the alignment state of the liquid crystal molecules 34a changes according to the voltage applied from the voltage application circuit 24, and the refractive power of the liquid crystal cylindrical lens 23 changes.

That is, when a sufficiently high voltage is applied to the liquid crystal, the liquid crystal cylindrical lens 23 has the same refractive power as a transparent flat plate.

Furthermore, by cutting off the voltage application, the liquid crystal cylindrical lens 23 has the same refractive power as a normal cylindrical lens.

Next, the astigmatism correction operation and the prevention of overcorrection will be specifically explained.

For example, nematic liquid crystal is used as the liquid crystal material of the liquid crystal cylindrical lens 23. This liquid crystal is selected to have a refractive index of 1.53 and 1.72 for ordinary rays and extraordinary rays, and a material with a refractive index of 1.53 is selected as the material for the cylindrical lens.

Liquid crystal cylindrical lens 23 made of such material
When the liquid crystal molecules 34a of the liquid crystal layer 34 are homogeneously aligned and the director of the liquid crystal molecules 34a is aligned with the direction of the transmission axis of the polarizing plate 22, a voltage is applied to the liquid crystal layer 34 as shown in FIGS. 2 and 3. In a state in which no voltage is applied, the refractive power is different in the axial direction and the main radial direction of the cylindrical surface formed on the lens substrate 31, as in a normal cylindrical lens. Therefore, when the polarizing plate 22 is arranged so that an extraordinary ray enters the calcite lens 21 and astigmatism occurs, if the liquid crystal cylindrical lens 23 is set to the state shown in FIGS. 2 and 3, the liquid crystal The refractive power difference of the cylindrical lens 23 corrects the axial astigmatism,
A dot-like focused spot can be formed.

Furthermore, when the polarizing plate 22 is rotated and placed at a position where ordinary rays of light are incident on the calcite lens 21, a sufficiently high voltage is applied to the liquid crystal cylindrical lens 23. Then, as shown in FIGS. 4 and 5, the liquid crystal 34a changes direction along the electric lines of force, and the apparent upper refractive index of the liquid crystal becomes 1.53, which is the same as the refractive index of the cylindrical lens. It will be the same. Therefore, the liquid crystal cylindrical lens 23 no longer has refractive power and becomes optically the same as a transparent flat plate, thereby preventing overcorrection by the cylindrical lens.

As described above, according to this embodiment, since the refractive power in the axial direction and the principal radial direction of the cylindrical surface of the liquid crystal cylindrical lens 23 can be changed arbitrarily, axial astigmatism can be effectively corrected, and overcorrection can be prevented. It can definitely be prevented.

FIG. 6 is a diagram showing the configuration of a variable focus lens according to a second embodiment of the present invention. This embodiment is an example in which a polarization plane rotating element made of liquid crystal is used as the polarizing means, and the other parts have the same structure as the first embodiment. 40 shown in the figure is a polarization plane rotation element, and the calcite lens 21
and the liquid crystal cylindrical lens 23. This polarization plane rotation element 40 includes polarizing plates 4 arranged opposite to each other.
43 TNSNS small cells were created between 1.42 and 1.42. A transparent conductive layer 44 is formed on opposing surfaces of polarizing plates 41 and 42 forming this TN liquid crystal cell 43, and a voltage application circuit 45 is connected to this transparent conductive layer 44.

According to the variable focus lens equipped with such a polarization plane rotation element 40, the same effects as in the first embodiment can be obtained, and furthermore, by applying a voltage to the TN liquid crystal cell 43, the polarization plane can be rotated. Therefore, the focal length can be changed by rotating the polarizing plate as in the first embodiment.

FIG. 7 is a diagram showing the configuration of a variable focus lens according to a third embodiment of the present invention. This embodiment is an example in which a liquid crystal lens 46 is used in place of the calcite lens 21 of the variable focus lens shown in FIG. That is, liquid crystal is used as a uniaxial crystalline material.

Even with such a variable focus lens, the first and second
Effects similar to those of the embodiment can be obtained.

FIG. 8 is a diagram showing the configuration of a fourth embodiment of the variable focus lens according to the present invention. This variable focus lens is an example in which a polarizing film is attached to a liquid crystal lens provided with a voltage application circuit. As the correction lens, the same one as the liquid crystal cylindrical lens 23 shown in FIG. 1 is used, and as the liquid crystal lens, the same one as the liquid crystal lens 10 shown in FIG. 9 is used. Further, the polarizing film 51 is provided on two surfaces of the flat glass substrate of the liquid crystal lens 10. The liquid crystal cylindrical lens 23 operates as a cylindrical lens when no voltage is applied to the liquid crystal layer 34 in which homogeneously initially aligned P-type liquid crystal is sealed, and when a sufficient voltage is applied, it exhibits refraction equivalent to that of a transparent flat plate. It operates as an optical element without power.

The variable focus lens configured in this manner operates as follows. Liquid crystal lens 10 and liquid crystal cylindrical lens 2
Operate in synchronization with 3. Here, when an extraordinary ray is incident and axial astigmatism occurs, the voltage application to the liquid crystal lens 10 is cut off. In this case, since no voltage is applied to the liquid crystal cylindrical lens 23, the refractive power differs between the axial direction and the main radial direction of the cylindrical surface of the liquid crystal cylindrical lens 23. As a result, astigmatism caused by the liquid crystal lens ]0 is corrected by the liquid crystal cylindrical lens 23.

On the other hand, after applying a sufficiently high voltage to the liquid crystal lens 10,
The liquid crystal lens 10 has refractive power for ordinary rays, and no axial astigmatism occurs. At this time, a sufficient voltage is also applied to the liquid crystal cylindrical lens 23, and the refractive power in the axial direction and main radial direction of the cylindrical surface disappears, and the liquid crystal cylindrical lens 23 operates equivalently to a transparent flat plate. Therefore, there is no need to worry about overcorrection caused by the liquid crystal cylindrical lens 23.

According to this embodiment, since the liquid crystal cylindrical lens 23 whose refractive power can be adjusted is used, even if the refractive power of the liquid crystal lens 10 changes continuously, it can be adequately coped with.
Astigmatism can be effectively corrected and over-correction can be reliably prevented.

Note that when using a general lens and a cylindrical lens in combination, since the cylindrical lens' main purpose is to correct astigmatism, there is a possibility that other aberrations such as curvature aberration may occur. The same can be said of the liquid crystal cylindrical lens 23 as a lens.

Therefore, by processing both side surfaces of the liquid crystal cylindrical lens 23, newly generated aberrations may be corrected.

In addition, in the first to fourth embodiments described above, correction lenses using liquid crystals are explained, or the correction lenses are not limited to liquid crystals, but other electro-optical materials may be used, or liquid may be sealed in an elastic film. You may also use a lens made of Note that in a lens formed by injecting a liquid into an elastic body, the amount of liquid injected is adjusted to change the shape of the elastic body and change its refractive power. It is desirable to use electrical drive means as a means for adjusting the amount of liquid to be injected.

〔Effect of the invention〕

According to the present invention, in a variable focus lens which has a variable focus function by combining a lens made of a material exhibiting uniaxial crystallinity and a polarizing means, the refractive power is adjusted to correct astigmatism caused by the lens. Since the variable focus lens is provided with a variable correction lens, it is possible to provide a variable focus lens that can effectively correct axial astigmatism, prevent overcorrection, and improve resolution.

[Brief explanation of the drawing]

Figures 1 to 5 are diagrams showing a first embodiment of the present invention.
The figure is a configuration diagram of the variable focus lens, Figures 2 and 4 are cross-sectional views of the liquid crystal cylindrical lens, Figures 3 and 5 are plan views of the liquid crystal cylindrical lens, and Figure 6 is the variable focus lens according to the second embodiment. 7 is a sectional view of a variable focus lens according to a third embodiment; FIG. 8 is a sectional view of a variable focus lens according to a fourth embodiment; FIG. 9 is a sectional view of a liquid crystal lens; FIG. 10 is a plan view of the liquid crystal lens shown in FIG. 9;
FIG. 11 is a diagram showing a combination of a polarizing plate and a liquid crystal lens, and FIG. 12 is a diagram for explaining astigmatism. 21... Calcite lens, 22... Polarizing plate, 23...
- Liquid crystal cylindrical lens, 24... Voltage application circuit, 40... Polarization plane rotation element, 51... Polarizing film. Figure 11 Gal, confused isotope l Figure 12 Figure 4 31 Figure 70-4a Figure Figure

Claims (2)

[Claims] (1) In a variable focus lens that has a variable focus function by combining a lens made of a material exhibiting uniaxial crystallinity and a polarizing means, correction in which the refractive power changes to correct astigmatism caused by the lens. A variable focus lens characterized by comprising a lens. (2) The correction lens is comprised of a liquid crystal lens in which a semi-cylindrical liquid crystal layer is formed, and the refractive power of the correction lens is changed by applying a voltage to the liquid crystal layer. The variable focus lens according to 1.