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 program memory which
stores therein a plurality of mocking design data with respect to a group
of parameters having any of a plurality of variable design parameters for
the zoom lens unit. The camera also has a control unit into which
designation information is inputted by the user which designates any one
of the plurality of mocking design data and a control unit which controls
the variable design parameters based on the mocking design data
designated by the designation information, so that a desired optical
property can easily be obtained.