Optical system and image pickup apparatus

1. An image pickup apparatus comprising:

a substrate;

an image pickup element on the substrate to convert a converged light flux to electronic signals;

an image-taking optical element positioned so as to converge a light flux from an object onto the image pickup element;

a light shielding member to house the image pickup element and the image-taking optical element;

a controlling device to control an output of the electronic signals and controlling the image pickup element; and

a refracting power-variable optical element,

wherein the refracting power-variable optical element comprises:

a first fluid member having a first refractive index and having an electrical conductivity;

a second fluid member having a second refractive index, which is different from the first refractive index, and having an insulative property, the second fluid member having no affinity for the first fluid member and having a same density as the first fluid member;

a shell member, in which the first fluid member and the second fluid member are filled and sealed, the shell member being made of an insulative material and having a opening portion to pass a light flux so that the light flux passed through the first fluid member and the second fluid member;

a first electrode contacting the first fluid member;

a second electrode installed at the shell member; and

an electric voltage-supplying device to change a shape of the second fluid member in the shell member by changing a wetting property of the shell member for the second fluid member by supplying an electric voltage between the first fluid member and the shell member.

2. The image pickup apparatus of claim 1 , wherein the refracting power-variable optical element further comprises a sealing member to seal the opening portion of the shell member, and the sealing member has a light transmittance and has an aspherical optical surface on at least one surface of he sealing member.

3. The image pickup apparatus of claim 2 , wherein the aspherical optical surface is capable of correcting an aberration, which is generated when the light flux is passed through the first fluid member and the second fluid member.

4. The image pickup apparatus of claim 1 , wherein the refracting power-variable optical element is positioned at an object side of the image-taking optical element.

5. The image pickup apparatus of claim 4 , wherein the image-taking optical element includes an optical element, which is the closest to the object, and the optical element is the sealing member.

6. The image pickup apparatus of claim 1 , wherein the refracting power-variable optical element further comprises an IR cutting filter to cut an infrared light and to seal the opening portion of the shell member.

7. The image pickup apparatus of claim 1 , wherein the refracting power-variable optical element further comprises:

a memory to store a relation between a value of the electric voltage supplied by the electric voltage-supplying device and a shape of the second fluid member in response to the value of the electric voltage; and

an electric voltage controlling device to control the electric voltage supplied by the electric voltage-supplying device according to the relation stored in the memory.

8. The image pickup apparatus of claim 1 , wherein the refracting power-variable optical element conducts an adjustment of a focus length with the electric voltage supplied by the electric voltage-supplying device.

9. The image pickup apparatus of claim 1 , wherein the refracting power-variable optical element conducts a focus adjustment with the electric voltage supplied by the electric voltage-supplying device.

10. The image pickup apparatus of claim 1 , wherein the refracting power-variable optical element shifts an optical axis of the refracting power-variable optical element to conform to an optical axis of the image-taking optical element with the electric voltage supplied by the electric voltage-supplying device.

11. The image pickup apparatus of claim 1 , wherein the refracting power-variable optical element tilts an optical axis of the refracting power-variable optical element to conform to an optical axis of the image-taking optical element with the electric voltage supplied by the electric voltage-supplying device.

12. An optical system comprising:

an optical aperture to confine an amount of a light flux passed through the optical aperture; and

a refractive power-variable optical element comprising:

a first fluid member having a first refractive index and having an electrical conductivity;

a second fluid member having a second refractive index, which is different from the first refractive index, and having an insulative property, the second fluid member having substantially no affinity for the first fluid member and having a substantially same density as the first fluid member;

a shell member, in which the first fluid member and the second fluid member are filled and sealed, at least a part of the shell member being made of an insulative material so that a light flux passes through the first fluid member and the second fluid member;

a first electrode contacting the first fluid member;

a second electrode installed at the shell member; and

an electric voltage-supplying device to change a shape of an interface between the first fluid member and the second fluid member by supplying an electric voltage between the first fluid member and the shell member,

wherein when a curvature radius of the interface between the first fluid member and the second fluid member has the minimum absolute value, a direction from a top of the interface to a center of curvature radius of the interface conforms to a direction from the top of the interface to the optical aperture.

13. The optical system of claim 12 , wherein the shell member has at least a curved surface, and a curvature radius of the curved surface of the shell member and a curvature radius of the interface between the first fluid member and the second fluid member have the same sign, when the curvature radius of the interface between the first fluid member and the second fluid member has the minimum absolute value.

14. The optical system of claim 12 , further comprising an optical element, which is adjacent to or contacts the refractive power-variable optical element,

wherein the shell member is a parallel plane plate, and a curvature radius of at least an optical surface of the optical element and a curvature radius of the interface between the first fluid member and the second fluid member have the same sign, when the curvature radius of the interface between the first fluid member and the second fluid member has the minimum absolute value.

15. The optical system of claim 13 , wherein a refractive power of the curved surface of the shell member and a refractive power of the interface between the first fluid member and the second fluid member have a different sign from each other, when the curvature radius of the interface between the first fluid member and the second fluid member has the minimum absolute value.

16. The optical system of claim 14 , wherein a refractive power of the optical surface of the optical element and a refractive power of the interface between the first fluid member and the second fluid member have a different sign from each other, when the curvature radius of the interface between the first fluid member and the second fluid member has the minimum absolute value.

17. The optical system of claim 12 , wherein each curvature radius of two surfaces of the shell member, where the light flux passes through and are boundary surfaces to outer air, and the curvature radius of the interface between the first fluid member and the second fluid member have the same sign, when the curvature radius of the interface between the first fluid member and the second fluid member has the minimum absolute value.

18. The optical system of claim 12 , wherein the following relations are satisfied:

when ni>no, |Rf|>|Rn|

when ni<no, |Rf|<|Rn|

where ni represents a refractive index of a fluid member nearer to the optical aperture among the first fluid member and the second fluid member; no represents a refractive index of a fluid member farther from the optical aperture among the first fluid member and the second fluid member; |Rf| represents an absolute value of a curvature radius of the interface between the first fluid member and the second fluid member when an object, which is positioned at first position, is to be focused by the optical system; and |Rn| represents an absolute value of a curvature radius of the interface between the first fluid member and the second fluid member when an object, which is positioned at second position being nearer than the first position from the optical system, is to be focused by the optical system.

19. The optical system of claim 12 , further comprising a main lens, which is positioned at a position farther from an object than the refractive power-variable optical element.

20. The optical system of claim 19 , wherein the optical aperture is positioned at a position adjacent to the refractive power-variable optical element and the main lens.

21. The optical system of claim 19 , wherein the following relation is satisfied:

| f′|/f> 5

wherein |f′| is an absolute value of a focus length of the refractive power-variable optical element when the absolute value becomes maximum in a range of object distance, which the optical system can focus; and f represents a focus length of the main lens.

22. The optical system of claim 12 , wherein the shell member is capable of cutting an infrared light.

23. An image pickup apparatus comprises:

the optical system of claim 12 ; and

an image pickup element to convert a light flux converged by the optical system to electronic signals.