A camera is provided which is adapted to receive a photographic lens having a diaphragm. The camera includes a detection unit configured to execute electric charge accumulation for detecting a defocus amount when the diaphragm is in a state having a first aperture value, and a controller configured to, when causing the diaphragm to perform an aperture reducing operation from the first aperture value to a second aperture value, cause the diaphragm to start the aperture reducing operation without waiting for completion of the electric charge accumulation for detecting the defocus amount by the detection unit.