Lens-interchangeable cameras which include a camera body and a lens barrel which can be attached and detached to and from a substantially circular opening formed on the front of the camera body are known in the art (e.g., Patent Literatures 1 and 2).
This type of camera body is provided on the edge of the opening thereof with a plurality of (e.g., three) body-side bayonet lugs which project toward the inner peripheral side and is provided behind each body-side bayonet lug with a biaser which produces a rearward biasing force. On the other hand, the interchangeable lens barrel is provided at the rear end thereof with a plurality of (e.g., three) lens-side bayonet lugs which project toward the outer peripheral side.
When the interchangeable lens barrel is mounted to the camera body, firstly the lens-side bayonet lugs are inserted into the camera body through a plurality of circular-arc openings, each of which is formed between adjacent body-side bayonet lugs, and the lens-side bayonet lugs are positioned immediately behind the body-side bayonet lugs, respectively, by rotating the lens barrel on its optical axis. Thereupon, each lens-side bayonet lug is biased to move rearward by the associated biaser, and the lens-side mount surface that is formed on the lens barrel comes into contact, from the forward direction, with the body-side mount surface that is formed on the camera body, so that the lens barrel is fixedly mounted to the camera body.
The lens barrel and the camera body are each provided with contact members, and the contact members of the lens barrel and the contact members of the camera body are electrically connected only when the lens barrel and the camera body are connected at a predetermined relative rotational angular position, and therefore, the lens barrel and the camera body need to be connected at the predetermined relative rotational angular position.
To this end, the body-side bayonet lugs, the circular-arc openings and the lens-side bayonet lugs are each intentionally made mutually different in lengthwise dimension (circumferential length) so as to allow each lens-side bayonet lug to be loosely engaged into only the predetermined circular-arc opening.
Accordingly, even if one attempts to connect the lens barrel and the camera body to each other at a position other than the predetermined relative rotational angular position, the long-size body-side bayonet lug is prevented from entering the camera body by the short-size circular-arc opening, and therefore, there is no possibility of the lens barrel being mistakenly mounted to the camera body at any incorrect relative rotational angular position.