A still camera which is provided with an indexible socket for a holder of percussively ignitable flash lamps can be used with an electronic flash unit whose base can be separably attached to the socket when the flash lamp holder is removed. The impeller which serves to initiate the ignition of the flash lamps performs the additional function of closing a switch in the casing of the electronic flash unit to thus complete the circuit of the source of artificial light in response to actuation of the camera release. The casing of the electronic flash unit can be provided with a base which is indexible with the socket or with a fixedly mounted base; in the latter instance, the attachment of the casing to the housing of the camera results in disengagement of the socket from the film transporting mechanism which normally serves to index the socket during transport of photographic film by the length of a frame.