Apparatus for driving sub-mirror in single lens reflex camera

Claim 1

In a single lens reflex camera of the type which includes: a housing; finder optical system; a photosensitive element for receiving the light transmitted through a photographing lens of said camera; a first supporting member one end of which is supported swing movably about an axis within said housing; a main mirror having a light transmitting portion formed therein, said main mirror being supported by said first supporting member for movement between a first position and a second position with the swing movement of said first supporting member so that in the first position said main mirror reflects the photographing light transmitted through the photographing lens toward the finder optical system and in the second position said main mirror does not reflect said photographing light and blocks the inverse incident light coming from said finder optical system; a second supporting member mounted on said first supporting member swing movably about an axis; and a sub-mirror mounted on said second supporting member and being movable between a third position and a fourth position with the swing movement of said second supporting member so that in the third position said sub-mirror reflects the photographing light transmitted through said light transmitting portion of the main mirror toward said photosensitive element and in the fourth position said sub-mirror blocks the inverse incident light transmitted through the finder optical system and said light transmitting portion and does not reflect said photographing light, the improvement comprising: a spring supported by said housing; a stationary member provided within said housing; a spring anchoring part formed integrally with said second supporting member and being biased by the working end of said spring for transmitting said biasing force to said sub-mirror, said spring anchoring part being disposed on said second supporting member in such manner that when said main mirror is in the first position it biases said sub-mirror to the third position, when said main mirror is in the second position it biases said sub-mirror to the fourth position and when said sub-mirror is in a particular position between said third and fourth positions, the direction of biasing force is reversed; and a branched part formed integrally with said second supporting member and comprising first and second branches opposed to each other so that said stationary member may be present between and apart from the first and second branches, said first and second branches remain out of contact with said stationary member when said sub-mirror is in the third position and in the fourth position, said first branch comes into contact with said stationary member at the initial step of movement of said main mirror from the first position to the second one so that said sub-mirror is moved from the third position to said particular position with a further movement of said main mirror against the biasing force of said spring thereby reversing the direction of the biasing force of said spring at said particular position, and said second branch comes into contact with said stationary member at the initial step of movement of said main mirror from the second position to the first one so that said sub-mirror is moved from the fourth position to said particular position with a further movement of said main mirror against the biasing force of said spring thereby reversing the direction of the biasing force of said spring.