Abstract: A slide member is slid by the user for adjusting the value of an exposure parameter, such as exposure-aperture size or exposure duration. The slide member has an inoperative setting and various operative settings, some of which are associated with different exposure-parameter values, others of which are additionally or alternatively associated with other functions and/or operating modes, the user necessarily often referring to the slide member because of its multi-purpose control actions. Electrical switch means are furthermore responsive to the setting of the slide member. A mechanical indicator mechanism of simple design, involving in the preferred embodiment a blocking blade coupled to the slide member and moving into and out of a little indicator window, quickly indicates to the user whether the slide member is in its inoperative setting or one of its various operative settings.