An imaging apparatus includes a sensor configured to photoelectrically convert light from an object to output a signal, a selection unit configured to select one of a first exposure control mode and a second exposure control mode having an exposure changing amount per unit time larger than that of the first exposure control mode, and a controller configured to perform control to transmit diaphragm control information generated based on the output signal from the sensor, first information, and second information to a connected lens unit, wherein the first information is about the exposure control mode selected by the selection unit, and the second information is speed information of a diaphragm unit corresponding to the lens unit.