A camera is provided which is configured to receive a photographic lens having a diaphragm. The camera includes a defocus amount detection unit configured to detect first information corresponding to a defocus amount, from light passing through the photographic lens mounted on the camera; an acquisition unit configured to acquire second information corresponding to an image-forming position from a lens position output unit provided on the photographic lens; and an image-forming position prediction unit configured to predict a change in image-forming position based on a change in the second information and a plurality of the past first information stored in a memory, wherein the image-forming position prediction unit predicts the image forming position in consideration of third information corresponding to time required for diaphragm driving that is acquired from a diaphragm driving time prediction unit provided on the photographic lens.