A group of optical elements of a zoom lens unit has variable-focal-length lenses whose optical properties can be adjusted. A camera having this zoom lens unit incorporated therein includes a control unit into which control information, with respect to any of a plurality of variable design parameters for the zoom lens unit, is inputted by the user. The camera also has a processing unit for obtaining an optical parameter of the zoom lens unit through a simulation operation when the variable design parameters are controlled based on the control information, a display unit which displays the results of the simulation operation that is carried out by the processing unit, and a photographing control unit for controlling the variable design parameters based on the control information, so that a desired optical property can easily be obtained.