A control apparatus includes a calculator that calculates a target dimming rate of a projection display apparatus based on a feature quantity of image data, a diaphragm controller that controls a diaphragm position of a diaphragm based on a target diaphragm position corresponding to the target dimming rate, and a light source controller that controls a light quantity of a light source based on the target dimming rate and a dimming rate of the diaphragm at least until the diaphragm position of the diaphragm matches the target diaphragm position.