Push button switch

1. A push button switch comprising:

a push button positioned on a switch base to be supported thereby in a manner to prevent said push button from coming off said switch base;

a biasing member positioned between said push button and said switch base at a substantially center of said push button to bias said push button in a direction away from said switch base;

a switching element having a press portion, said switching element being provided at a position offset from an axis of said push button;

a press projection and a rocking projection which are formed on said push button on opposite sides of said center thereof, respectively, said press projection projecting to be associated with said press portion of said switching element; and

a fulcrum formed on said switch base to be associated with said rocking projection,

wherein said rocking projection and said fulcrum are disengaged from each other when said push button is in a non-depressed position,

wherein said rocking projection comes into contact with said fulcrum when said push button is half depressed, and

wherein said push button turns about said fulcrum when said push button is further depressed following said half depression of said push button.

2. The push button switch according to claim 1 , wherein said biasing member comprises a coil spring.

3. The push button switch according to claim 1 , wherein said half depression of said push button causes said press projection to half press said press portion of said switching element so as to perform a first switching operation, and

wherein said further depression of said push button, following said half depression of said push button, causes said press projection to further press said press portion of said switching element so as to perform a second switching operation.

4. The push button switch according to claim 1 , wherein each of said fulcrum and said rocking projection is elongated in a direction substantially orthogonal to a straight line connecting said center of said push button and said press projection of said push button.

5. The push button switch according to claim 4 , wherein respective contacting surfaces of said press projection and said rocking projection, which come into contact with each other when said push button is half depressed, are one and the other of a concave cylindrical surface and a convex cylindrical surface.

6. The push button switch according to claim 4 , wherein said push button has an oval shape in plan view, and

wherein each of said press projection and said rocking projection is elongated in a major axis of said push button.

7. The push button switch according to claim 1 , wherein said push button switch is incorporated in a camera so that said push button serves as a shutter release button,

wherein said switch base comprises an outer flange portion, a cylindrical portion and a bottom wall, in that order in a direction from top to bottom of said camera, and

wherein said cylindrical portion is fitted in a hole formed on an exterior wall of said camera.

8. The push button switch according to claim 1 , wherein said rocking projection comes into contact with said fulcrum while said press projection half presses said press portion of said switching element when said push button is half depressed, and

wherein said push button turns about said fulcrum so that said press projection fully presses said press portion of said switching element when said push button fully depressed following said half depression of said push button.

9. The push button switch according to claim 1 , wherein said switching element is positioned below said switch base,

wherein a through hole is formed on said switch base so that said press projection can press said press portion of said switching element through said through hole when said push button is depressed.

10. The push button switch according to claim 7 , wherein said switching element comprises a photometric switch and a release switch, and

wherein said press projection half presses said press portion of said switching element to switch ON said photometric switch when said shutter release button is half depressed, and

wherein said press projection fully presses said press portion of said switching element to switch ON said release button when the shutter release button is fully depressed following said half depression of said shutter release button.

11. A shutter release mechanism of a camera, comprising:

a switch base having a recess which is fixed to an exterior wall of said camera;

a shutter release button fitted in said recess to be freely movable in said recess along an axis of said shutter release button within a predetermined range of movement;

a spring for biasing said shutter release button in a direction away from a bottom wall positioned at the bottom of said recess;

a switching element positioned below said switch base, and having a press portion which is disposed at a position offset from an axis of said shutter release button;

a press projection and a rocking projection which are formed on said shutter release button to project inwards, toward said bottom wall of said switch base, from opposite ends of said shutter release button, respectively, said press projection projecting so as to face said press portion of said switching element through a through hole formed on said switch base; and

a fulcrum formed on said switch base to face said rocking projection,

wherein said rocking projection and said fulcrum are disengaged from each other when said shutter release button is in a non-depressed position,

wherein said rocking projection comes into contact with said fulcrum while said press projection half presses said press portion of said switching element when said shutter release button is half depressed, and

wherein said shutter release button turns about said fulcrum while said press projection fully presses said press portion of said switching element when the shutter release button is fully depressed following said half depression of said shutter release button.