1. An imaging lens comprising:
a first lens group having negative refractive power;
a second lens group having positive refractive power;
a third lens group having positive refractive power; and
a fourth lens group, arranged in this order from an object side to an image plane side,
wherein said first lens group has refractive power stronger than that of the second lens group, the third lens group, or the fourth lens group, and includes a first lens having a concave surface facing the image plane side,
said second lens group includes a second lens having a meniscus lens shape with a concave surface facing the object side,
said fourth lens group includes a third lens having positive refractive power and a fourth lens having negative refractive power, and
said imaging lens is arranged to satisfy the following expression when the imaging lens as a whole lens system has a focal length f, and the first lens group, the second lens group, and the third lens group have a composite focal length Fa:
0.3<fFa<1.0
2. The imaging lens according to claim 1, wherein said imaging lens is arranged to satisfy the following relation when the first lens group has a focal length F1:
\u22123.0<F1f<\u22121.0
3. The imaging lens according to claim 1, wherein said first lens group further includes a fifth lens having a meniscus lens shape with a concave surface facing the image plane side.
4. The imaging lens according to claim 1, wherein said imaging lens is arranged to satisfy the following relation when the second lens group has a focal length F2:
2.0<F2f<25
5. The imaging lens according to claim 1, wherein, said fourth lens group includes the third lens having a focal length fp and the fourth lens having a focal length fn so that the imaging lens satisfies the following conditional relation:
0.5<|fpfn|<2.0
6. The imaging lens according to claim 1, wherein said fourth lens group includes the third lens having an Abbe’s number \u03c5dp and the fourth lens having an Abbe’s number \u03c5dn so that the imaging lens satisfies the following conditional relation:
20<\u03c5dp\u2212\u03c5dn
7. The imaging lens according to claim 1, wherein said fourth lens group includes the third lens having an Abbe’s number \u03c5dp and the fourth lens having an Abbe’s number \u03c5dn so that the imaging lens satisfies the following relation:
\u03c5dp>\u03c5dn
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1-9. (canceled)
10. A variable capacitance element comprising:
a substrate; a fixed electrode provided on the substrate;
a plate-like movable element provided on the substrate at a position opposing the fixed electrode so as to be displaced close to and away from the fixed electrode;
a movable electrode provided in a region of the movable element which faces the fixed electrode, the movable electrode having a capacitance in conjunction with the fixed electrode which is changed when the movable electrode is moved close to or away from the fixed electrode; and
a driver arranged to drive the movable element in a direction in which the movable element is moved close to or away from the fixed electrode; wherein
the movable element is provided with a warp adjusting film by which a direction in which a central portion of the movable element warps with respect to peripheral portions thereof is maintained in one of a direction of warping in a convex form toward the fixed electrode and a direction of warping in a concave form away from the fixed electrode.
11. The variable capacitance element according to claim 10, wherein, if a sum of an internal stress generated during formation of the warp adjusting film on the movable element and a thermal stress generated by a difference in thermal expansion between the movable element and the warp adjusting film defines a total stress, the movable element and the warp adjusting film are configured such that, for a change in temperature, the total stress maintains the warping direction of the movable element so as to be unidirectional.
12. The variable capacitance element according to claim 10, wherein the warp adjusting film is configured to warp the movable element in the direction of warping in the convex form toward the fixed electrode.
13. The variable capacitance element according to claim 10, wherein the warp adjusting film is an insulating film and is arranged to cover, with a compressive stress, a region of the movable element which faces the fixed electrode, the movable electrode is provided on the movable element with the insulating film provided therebetween, and the insulating film uses the compressive stress to warp the movable element and the movable electrode in the direction of warping in the convex form toward the fixed electrode.
14. The variable capacitance element according to claim 10, wherein the warp adjusting film is configured so as to warp the movable element in the direction of warping in the concave form away from the fixed electrode.
15. The variable capacitance element according to claim 10, wherein the fixed electrode is provided with an insulating stopper which abuts against the movable element when the movable element is displaced toward the fixed electrode.
16. The variable capacitance element according to claim 10, wherein the movable element is provided with an insulating stopper which abuts against the fixed electrode when the movable element is displaced toward the fixed electrode.
17. The variable capacitance element according to claim 15, wherein the stopper is provided in a portion of a region where the fixed electrode and the movable element oppose each other.
18. The variable capacitance element according to claim 16, wherein the stopper is provided in a portion of a region where the fixed electrode and the movable element oppose each other.
19. The variable capacitance element according to claim 10, wherein the fixed electrode is a transmission line arranged to transmit a high frequency signal.
20. The variable capacitance element according to claim 10, wherein a different substrate is provided opposite said substrate with the movable element provided therebetween, and the different substrate is provided with a driving electrode which defines the driver and uses an electrostatic force to displace the movable element.
21. The variable capacitance element according to claim 20, wherein the different substrate include at least one insulating stopper which abuts against the movable electrode when the movable element is displaced toward the different substrate.
22. The variable capacitance element according to claim 10, wherein said substrate includes at least one supporting portion disposed at an end of said substrate and arranged to support said movable element.
23. The variable capacitance element according to claim 22, wherein at least one support beam extends between said movable element and said at least one supporting portion so as to connect said movable element to said at least one supporting portion.
24. The variable capacitance element according to claim 10, wherein the warp adjusting film is made of silicon oxide.
25. The variable capacitance element according to claim 23, wherein said at least one support beam is made of a low resistive monocrystal silicon material.
26. The variable capacitance element according to claim 22, wherein said at least one supporting portion is made of a low resistive monocrystal silicon material.
27. The variable capacitance element according to claim 20, wherein the different substrate is attached to at least one supporting portion of said substrate by anode coupling.
28. The variable capacitance element according to claim 10, wherein the substrate is made of a high resistive monocrystal silicon material.
29. The variable capacitance element according to claim 10, wherein the substrate is made of an insulating glass material.