Large aperture ratio interchangeable lens for a single lens reflex camera

A large aperture ratio interchangeable lens adapted to be mounted on the camera body of a single lens reflex camera of the TTL open photometry type comprising a lens body, a preset aperture ring rotatable with respect to the lens body for varying the lens aperture between an open F-value (f.sub.O) inherent to said lens and a desired F-value (f) by rotation of the aperture ring, a first signal member operatively associated with the aperture ring for transmitting to the camera body, by virtue of the location of the first signal member, a difference signal (f-f.sub.O) corresponding to the difference between the open F-value (f.sub.O) and the desired F-value (f) set by said aperture ring, the first signal member having a deviation from a predetermined position at which the position of the first signal member corresponds to the open F-value (f.sub.O) inherent to said lens in order to compensate for the difference between the quantity of light theoretically passing through said lens and the quantity of light actually passing through the lens, and a second signal member for transmitting to the camera body, by virtue of the location of the second signal member, a signal corresponding to said open F-value (f.sub.O), the second signal member having a deviation from a predetermined position at which the position of the second signal member indicates the open F-value (f.sub.O) of the lens, said deviation of the second signal member being equal to the deviation of the first signal member.