JPS60207110A - Image forming optical system with variable aberration - Google Patents

Abstract

PURPOSE:To control an image forming state by arranging a heat generating resistor which heats a medium so that an isolated position of the medium is heated independently. CONSTITUTION:One side of the heat generating resistor 4 is connected to a voltage impressing means 11 through an electrode 5, and the other is grounded or held at a constant potential. When the heat generating resistor 4 is impressed with a voltage by a voltage impressing means shown in a figure, a current flow in the heat generating resistor 4 to form a refractive index in the heat-effect medium 2, and the impressed voltage or the pulse impression time of a periodic pulse voltage is varied in this case to vary the heating value. Thus, the heating value varies and then the refractive index distribution in the heat-effect medium 2 also varies.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an imaging optical system capable of changing the state of aberration.

Conventionally, in imaging optical systems, in order to improve aberrations,
Alternatively, aberrations are controlled to generate predetermined aberrations, such as in soft focus.

Generally, in an optical system composed of a spherical lens group, an aspherical lens is used as a part of the surface to correct aberrations. However, the processing of aspherical lenses has the disadvantage that it requires advanced technology and is therefore prohibitively expensive.

Furthermore, some photographic lenses have a soft focus function by forming an entrance pupil in a special shape. However, in such a method, when the diameter of the aperture diaphragm is changed, the soft focus functions in response to the change in the diameter of the aperture, which is inconvenient for photographers who require flexibility in the soft focus function.

An object of the present invention is to provide an imaging optical system that can control the aberration state, in other words, the imaging state.

A further object of the present invention is to provide an imaging optical system that can change the imaging characteristics of any part on the imaging surface.

In the imaging optical system according to the present invention, an optical element capable of forming a refractive index distribution (111) is arranged in the imaging optical system in a medium whose refractive index is sufficiently changed by heat. The objective is to be achieved by utilizing within an imaging optical system the phenomenon of changing the direction of an incident light beam depending on the refractive index of the element.

The means for applying heat to the medium of the optical element disposed in the imaging optical system according to the present invention is constituted by a means capable of applying heat independently to a plurality of positions on the medium. Therefore, it is possible to apply a deflection effect to the light beam transmitted through the imaging optical system at any position within the optical system and at any arbitrary portion within the cross section of the transmitted light beam. The most common means for applying heat is a combination of a heating resistor and a means for applying voltage to the resistor, and in this case, the pattern of the heating resistor provided to the heat effect medium is It is possible to take a desired pattern shape according to the purpose.

The imaging optical system according to the present invention is a transmission type.

It goes without saying that both reflective and transmissive types are included, but both transmissive and reflective optical elements can be used.

As the thermal effect medium of the optical element used in the imaging optical system according to the present invention, examples of liquids having a temperature coefficient of negative refractive index include ethyl alcohol, benzene, ethyl ether, methylene iodide, water, and Carbon chloride etc. Solids include polystyrene, polycyclohegyl methacrylate, polymethyl methacrylate, fluorite (caF2), and rock salt.

Crystal, quartz glass, F'5 (product name: manufactured by Ohara Optical Co., Ltd.), and those with a positive temperature coefficient of refractive index include lithium niobate (LiNbO5), calcite, BK7,
BF6 (both product names: manufactured by Ohara Optical Co., Ltd.) etc. can be used.

1 to 3 are diagrams illustrating a photothermal deflection optical element used in the imaging optical system of the present invention.

The basic principle of this element is, for example, as shown in Nikkei Ellen's Figures 1 (A) and (B), in which the element is a transparent protective plate 1,
It is composed of a thermal effect medium 2 that forms a refractive index distribution by heat, an insulating layer 3, a heating resistor 4, an electrode 5, and a transparent plate 6. When a voltage is applied to the heat generating resistor 4, the heat generated forms a refractive index distribution 1o in the heat effect medium 2 in the shape shown in the figure, which connects portions of equal refractive index. When a beam of light 7 is incident on this portion, the wavefront is changed and a beam of light 9 is emitted as if it were diverging from a single point 8. The distance from the boundary surface of the thermal effect medium to the divergence origin (or convergence point) 8 is defined as f, and this is defined as the focal length.

The shape of the refractive index distribution formed in the medium of the element is a state in which the refractive index changes with respect to the amount of heat of the medium, that is, when the temperature of the medium is raised, the value of the refractive index becomes larger. It depends on whether it becomes smaller or smaller. If the value of the refractive index decreases as the temperature of the medium increases, the shape of the refractive index distribution will change as shown in Figure 1 (A) with the center at the position where heat is applied to the medium.
As shown in the figure, it has a mountain-shaped (convex) shape.

On the other hand, when the refractive index value of the medium increases as the temperature rises, the shape of the refractive index distribution becomes a valley shape (concave shape) centered on the position where heat is applied to the medium. Therefore, the light beam incident on such a chevron-shaped refractive index distribution becomes a diverging light beam after exiting from the refractive index distribution, and such a chevron-shaped refractive index distribution acts as a concave lens. Further, the light beam incident on the valley-shaped refractive index distribution becomes a convergent light beam after exiting from the refractive index distribution, and such a valley-shaped refractive index distribution acts as a convex lens.

FIG. 2 is a diagram illustrating means for applying an input voltage to the photothermal deflection optical element explained in FIG. It is held at a constant potential. When a voltage is applied to the heating resistor 4 by the voltage applying means shown in FIG. 2, a current flows in the heating resistor 4, and a refractive index distribution is formed in the thermal effect medium as described above. In this case, the amount of heat generated changes by changing the applied voltage or the pulse application time of the periodic pulse voltage. As a result of the change in the amount of heat generated, the refractive index distribution within the thermal effect medium also changes.

Figure 3 shows a reflection type element in contrast to the transmission type photothermal deflection optical element shown in Figures 1(A) and 2. Components with the same shoe number as the reference number indicate the same member. In FIG. 3, 13 is an aluminum light reflecting layer. When a parallel light beam 14 is incident on this element, the wavefront is converted by the refractive index distribution 10, and after being reflected by the light reflection layer 13, the wavefront is further converted by the refractive index distribution 10, so that it appears as if it diverged from the divergence origin 14. In the above, an example was shown in which the light flux 16 heats the heat generating resistor structure in the element described above, but as another heating means, a heat absorbing member attached to a heat effect medium is irradiated with light, laser, etc. Alternatively, the heat effect medium may be directly irradiated with light, laser, or the like.

FIGS. 4(A) and 4(B) are schematic front views showing one embodiment of the photothermal deflection optical element used in the imaging optical system of the present invention. The diagram shown in FIG. 4 shows the pattern in which the heating resistors 4 are arranged with respect to the thermal effect medium 2, and the size of the medium 2 matches the diameter of the optical system to which it is applied. It is formed by size. The element shown in FIG. 4(A) is
Heat generating resistors 4 are arranged in a matrix, and each heat generating resistor is connected to a voltage applying means via an electrode (not shown). In the element shown in FIG. 4(B), heating resistors 4 are arranged concentrically.

FIG. 5 is a cross-sectional view of a lens showing an embodiment of the imaging optical system according to the present invention, which is particularly designed to control spherical aberration. This lens configuration is a so-called Gaussian lens with symmetrical lens groups arranged on both sides of the aperture 20, with the lens group placed on one side of the aperture being farthest from the aperture, Positive meniscus lens with concave side (
21, 26) and a biconvex lens (22, 25) near the aperture.
) and biconcave lenses (23, 24), and the concave surface faces the aperture side. 27 is a photothermal deflection optical element as shown in FIGS. 4(A) and 4(B), which is arranged near the aperture. The reason why this element 27 is arranged near the aperture 20 is that when controlling spherical aberration, acting on the light beam near the aperture tends to have a large effect on the spherical aberration.

It is sufficient to operate the element 27 so as to affect the spherical aberration in the mirror. Further, if the spherical aberration of the lens system (21 to 26) has been well corrected, it is sufficient to generate flare in the lens system and operate the element 27 in a soft manner. For this reason, the part of the element □27 that acts on the luminous flux is only the peripheral part of the element 27. Therefore, when using the element shown in FIG. 4(A), the heating resistor 4 arranged in the matrix Of these, it is only necessary to generate heat from the heating resistor arranged on the outer periphery. Further, when using the element shown in FIG. 4(B), it is sufficient to generate heat only from the heating resistor 4 on the outer periphery arranged concentrically.

As mentioned above, when correcting the spherical aberration of the lens system, if the spherical aberration of the lens system is excessively generated, and therefore the element 27 generates an under-spherical aberration to correct the spherical aberration, the heat of the element 27 is As the effect medium 2, a medium with a temperature coefficient of refractive index may be used. On the contrary, the spherical aberration of the lens system is under-generated, and therefore the element 27 generates an over-spherical aberration, causing spherical aberration, and as mentioned above, flare is generated in the lens system, causing the lens system to have a soft focus. iif:, the spherical aberration to be generated may be either over or under spherical aberration, and therefore a medium with a positive or negative refractive index coefficient can be used as the thermal effect medium. It is.

FIG. 6 shows an example of an optical element used in the imaging optical system of the present invention.The difference from the optical element shown in FIG. 1(A) is that the lens itself is used as a transparent cutting plate of the optical element. This is what we are using. That is, the optical element shown in FIG. 1(A) uses the transparent cut plate 6 as the end plate of the element, whereas the element shown in FIG. 6 uses the lens 28 as the end plate of the optical element. On the other hand, if the transparent plate 6 of the optical element shown in FIG. 1(A) is shaped, the letterpress 6 is used as a lens. By adopting such a shape of the optical element, it is possible to downsize the optical system.

In the above embodiment, the optical element '+14 structure is a transmission type, and the imaging optical system is also a transmission type consisting of a lens. It is obvious that imaging optical systems of various configurations can be assembled using reflecting mirrors.

FIG. 7 is a diagram showing another embodiment of the imaging optical system of the present invention.
FIG. 3 is a diagram illustrating correction of distortion aberration of an imaging optical system. 7th
The image forming optical system shown in the figure consists of two convex lenses placed on both sides of a concave lens 32. A diaphragm 30 is provided between a convex lens 31 and a concave lens 320. 34 is provided at a more distant position. In this manner, when correcting distortion aberration, it is possible to control the distortion more efficiently by acting on the light beam at a position further away from the diaphragm 30. When correcting distortion aberration, it is desirable that the optical element 34 act on a light beam with a large internal angle, so of the heating resistors arranged in the optical element 34, only the heating resistors located away from the optical axis generate heat. Just let it happen.

When correcting distortion aberration, the imaging optical system (31° 32.3
If the distortion generated only in 3) is positive, that is, if it is pincushion distortion, the thermal effect medium used in the optical element 34 has a temperature coefficient of negative refractive index; When the distortion aberration generated only in the image optical system is negative, that is, when it is a joint type distortion aberration, the thermal effect medium used in the optical element 34 has a temperature coefficient of a positive refractive index.

[Brief explanation of drawings]

Figures 1 (A) and (B) + Figures 2 and 3 are diagrams for explaining the configuration and operating principle of the photothermal deflection element used in the imaging optical system of the present invention, and Figure 4 (A) . (B) is a schematic front view of a photothermal deflection element used in the imaging optical system of the present invention, FIG. 5 is a diagram showing an embodiment of the imaging optical system according to the present invention, and FIG. FIG. 7 is a diagram showing another embodiment of the photothermal deflection element used in the imaging optical system, and FIG. 7 is a diagram showing another embodiment of the imaging optical system according to the present invention. DESCRIPTION OF SYMBOLS 1...Transparent protective plate, 2...Thermal effect medium, 3...Insulating layer, 4...Heating resistor, 5...Electrode, 6...Transparent substrate, Applicant: Canon Corporation No. 10(A)

Claims (1)

[Scope of Claims] (1) An imaging optical system, comprising an optical element disposed in the imaging optical system and capable of controlling the imaging characteristics of the imaging optical system, the optical element being able to control the imaging characteristics of the imaging optical system. It consists of a medium that forms a refractive index distribution therein, and a heating means that applies heat to a desired position of the medium, and the heating means is formed of a heating resistor and means for applying a voltage to the resistor, and A variable aberration imaging optical system characterized in that a heating resistor for heating a medium is arranged so as to be able to independently heat isolated positions of the medium. (2) The optical element is disposed near the aperture of the imaging optical system, and the optical element acts on the light beam at a position away from the optical axis to control spherical aberration. The variable aberration imaging optical system according to item 1. (8) The medium of the optical element is a medium having a positive temperature coefficient of refractive index, and the variable aberration according to claim 2 corrects under spherical aberration that often occurs in the imaging optical system. Imaging optical system. (4) The medium of the optical element is a medium having a temperature coefficient of negative refractive index, and the variable aberration according to claim 2 corrects excessive spherical aberration that often occurs in the imaging optical system. Imaging optical system. 2. The variable aberration imaging optical system according to claim 1, which controls distortion aberration by acting on the aberration. (6) The variable aberration lens according to claim 5, wherein the optical element is a medium having a positive temperature coefficient of refractive index, and the variable aberration lens corrects barrel-shaped distortion generated by the imaging optical system. Image optical system. (7) The variable aberration imaging optical system according to claim 5, wherein the optical element is a medium having a temperature coefficient of negative refractive index, and the variable aberration imaging optical system corrects pincushion distortion generated by the imaging optical system. .